A color-image reader reads a recorded color image from a recording medium, and has an image sensor for sensing the color image as at least a first and second regular series of monochromatic image signals during a regular reading operation. A first optimal exposure period is determined regarding the first regular series of image signals, and a second optimal exposure period is determined regarding the second regular series of image signals. A first set of color-correction parameters is determined based on a first provisional series of image signals, sensed from the color image by the image sensor over the first optimal exposure period. A second set of color-correction parameters is determined based on a second provisional series of image signals, sensed from the color image by the image sensor over the second optimal exposure period. A color balance is performed among the first and second regular series of image signals by using the first and second sets of color-correction parameters.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a color-image reader for optically and 
electronically sensing and reading a color image, which is recorded on a 
suitable recording medium, such as a transparency, a sheet of paper or the 
like. 
2. Description of the Related Art 
Such a color-image reader per se is well known, and is used, for example, 
in peripheral equipment associated with an image-processing computer for 
retrieving a color image. As a general representation, a color-image 
reader includes a solid-state line image sensor, such as a CCD 
(charge-coupled device) image sensor, a suitable light source for 
cyclically and successively illuminating the recording medium with primary 
color light rays: red-light rays, green-light rays and blue-light rays. 
The CCD line image sensor includes a plurality of CCD elements aligned with 
each other, and each of the CCD elements generates and accumulates an 
electric charge in accordance with a received amount of monochromatic 
light rays (red, green, blue). As is well known, the CCD line image sensor 
possesses an electronic shutter function, and a time of 
electric-charge-accumulation or a time of exposure may be suitably 
controlled and regulated by using the electronic shutter function. As long 
as the CCD line image sensor is exposed to the monochromatic light rays, a 
degree of electric charge in each of the CCD elements is gradually 
increased, and the CCD elements finally reach saturation with the 
accumulated electric charges. 
In operation, the recording medium is intermittently moved with respect to 
the CCD line image sensor such that the recording medium is scanned in a 
step-by-step manner with the CCD line image sensor. During each stoppage 
of the recording medium when being intermittently moved, the recording 
medium is subjected to one cycle of the successive emissions of the 
primary colors of light from the light source during each standstill of 
the transparent object, and the CCD line image sensor is successively 
exposed to the primary color light rays, passing through or reflected by 
the recording medium. 
During the exposure of the CCD line image sensor to the primary color light 
rays, three single-lines of monochromatic image-pixel signals are 
successively outputted from the CCD line image sensor. After the 
outputting of the three single-lines of monochromatic image-signals from 
the CCD line image sensor, the recording medium is moved with respect to 
the CCD line image sensor by one scan-pitch. Thus, when the 
above-mentioned scanning operation is completed, three frames of 
monochromatic image-pixel signals, corresponding to the primary colors, 
can be obtained and used to reproduce the recorded color image of the 
recording medium, for example, on a TV monitor. 
During the reading of the recorded color image from the recording medium, 
the exposure period, over which the CCD line image sensor is exposed to 
the monochromatic light rays, must be optimally regulated before the read 
color image can be obtained with the best contrast. Also, in order to 
reproduce the read color image with the best color balance, the 
three-frames of monochromatic image-pixel signals must be subjected to 
optimal color correction. Especially, as is well known when the recording 
medium is a transparency film, the color correction is critical, because a 
film material per se of the transparency film is colored. 
An optimal exposure period is varied in accordance with a change in 
transparency of a recorded color image due to the reading of another 
recording medium. Accordingly, the optimal exposure period must be 
determined in accordance with the transparency of the recording medium. 
Conventionally, prior to a regular scanning operation for sensing and 
reading the recorded color image from the recording medium, a pre-scanning 
operation is carried out in order to determine an optimal exposure period 
with respect to the recorded color image of the recording medium 
concerned. 
Nevertheless, conventionally, it is impossible to accurately determine the 
optimum exposure period, because a method for determining the optimum 
exposure period is based on an inaccurate assumption that there is a 
directly linear relationship between a time of exposure and a degree of 
electric charge accumulation in the CCD line image sensor, as discussed 
hereinafter in detail. 
On the other hand, conventionally, color-correction parameters necessary 
for the color correction are determined on the basis of the three frames 
of monochromatic image-pixel signals obtained by the above-mentioned 
pre-scanning operation. Nevertheless, the determination of the 
color-correction parameters also cannot be accurately performed, because 
the three-frames of monochromatic image-pixel signals, obtained by the 
pre-scanning operation, do not properly represent color characteristics of 
the recorded color image of the recording medium. Also, an accurate 
determination of the color-correction parameter for a negative color 
transparency film is especially difficult, because the negative color 
transparency exhibits a wider exposure latitude than that of a positive 
color transparency. 
Before accurate color-correction parameters can be obtained, the 
determination of the color-correction parameters should be based on three 
respective frames of monochromatic image-pixel signals derived from 
optimum exposure periods. Nevertheless, it is impossible to accurately 
determine the optimum exposure period with the conventional method as 
previously mentioned. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a color-image 
reader, using a solid-state image sensor for optically and electronically 
sensing a recorded color image of a recording medium, wherein not only an 
exposure period but also color-correction parameters can be optimally and 
accurately determined, so that a recorded color image can be sensed and 
read from a recording medium with the best contrast and the best color 
balance. 
In accordance with the invention, there is provided a color-image reader 
for optically and electronically reading a recorded color image from a 
recording medium. The image reader comprises: an image sensor for sensing 
the color image as at least a first regular series of monochromatic 
image-pixel signals and as a second regular series of monochromatic 
image-pixel signals during a regular reading operation; a first 
optimal-exposure-period determiner for determining a first optimal 
exposure period with respect to the first regular series of monochromatic 
image-pixel signals; a second optimal-exposure-period determiner for 
determining a second optimal exposure period with respect to the second 
regular series of monochromatic image-pixel signals; a first 
color-correction-parameter determiner for determining a first set of 
color-correction parameters on the basis of a first provisional series of 
monochromatic image-pixel signals, which is sensed from the recorded color 
image by the image sensor over the first optimal exposure period 
determined by the first optimal-exposure-period determiner; and a second 
color-correction-parameter determiner for determining a second set of 
color-correction parameters on the basis of a second provisional series of 
monochromatic image-pixel signals, which is sensed from the recorded color 
image by the image sensor over the second optimal exposure period 
determined by the second optimal-exposure-period determiner. The first 
regular series of monochromatic image-pixel signals is processed by the 
first set of color-correction parameters, such that a first regular 
histogram, which is produced on the basis of the first regular series of 
monochromatic image-pixel signals, is generated over a first predetermined 
level-value range, and the second regular series of monochromatic 
image-pixel signals is processed by the second set of color-correction 
parameters, such that a second regular histogram, which is produced on the 
basis of the second regular series of monochromatic image-pixel signals, 
is generated over a second predetermined level-value range. 
The first predetermined level-value range and the second predetermined 
level-value range may substantially coincide with each other. Also, the 
first predetermined level-value range may be defined by an input range of 
a first image-signal processor for processing the first regular series of 
monochromatic image-pixel signals, and the second predetermined 
level-value range may be defined by an input range of a second 
image-signal processor for processing the second regular series of 
monochromatic image-pixel signals. 
Preferably, the first color-correction-parameter determiner comprises a 
first histogram-producer for producing a first histogram from the first 
provisional series of monochromatic image-pixel signals, a first effective 
minimum level-value calculator for calculating an effective minimum 
level-value from the first histogram, and a first effective maximum 
level-value calculator for calculating an effective maximum level value 
from the first histogram. The first regular series of monochromatic 
image-pixel signals is processed by the first set of color-correction 
parameters such that a range, defined by the first effective minimum 
level-value and the first effective maximum level-value, substantially 
coincides with the first predetermined level-value range. 
The first effective minimum level-value may be defined as a 
boundary-level-value of a predetermined area, which includes an actual 
minimum level-value, of the first histogram, and the first effective 
maximum level-value may be defined as a boundary-level-value of a 
predetermined area, which includes an actual maximum level-value, of the 
first histogram. 
Similarly, preferably, the second color-correction-parameter determiner 
comprises a second histogram-producer for producing a second histogram 
from the second provisional series of monochromatic image-pixel signals, a 
second effective minimum level-value calculator for calculating an 
effective minimum level-value from the second histogram, and a second 
effective maximum level-value calculator for calculating an effective 
maximum level value from the second histogram. The second regular series 
of monochromatic image-pixel signals is processed by the second set of 
color-correction parameters such that a range, defined by the second 
effective minimum level-value and the second effective maximum 
level-value, substantially coincides with the second predetermined 
level-value range. 
The second effective minimum level-value may be defined as a 
boundary-level-value of a predetermined area, which includes an actual 
minimum level-value, of the second histogram, and the second effective 
maximum level-value may be defined as a boundary-level-value of a 
predetermined area, which includes an actual maximum level-value, of the 
second histogram. 
The recording medium may be either a negative transparency film carrying a 
negative color image or a positive transparency film carrying a positive 
color image. In this case, the first regular series of monochromatic 
image-pixel signals and the second regular series of monochromatic 
image-pixel signals are derived from either the negative color image or 
the positive color image. When the recording medium is the negative 
transparency film, the color-image reader may further comprise a 
negative-to-positive converter for converting the first regular series of 
monochromatic image-pixel signals and the second regular series of 
monochromatic image-pixel signals into a first regular series of positive 
monochromatic image-pixel signals and a second regular series of positive 
monochromatic image-pixel signals, respectively. Also, when the recording 
medium is the positive transparency film, the color-image reader may 
further comprise a positive-to-negative converter for converting the first 
regular series of monochromatic image-pixel signals and the second regular 
series of monochromatic image-pixel signals into a first regular series of 
negative monochromatic image-pixel signals and a second regular series of 
negative monochromatic image-pixel signals, respectively. 
The image sensor may exhibit a characteristic curve, having at least a 
partial linear section, describing a relationship between a level-value of 
an image-pixel signal and an exposure period over which the image sensor 
is exposed to each of first monochromatic light rays and second 
monochromatic light rays, which correspond to the first regular series of 
monochromatic image-pixel signals and the second regular series of 
monochromatic image-pixel signals, respectively. 
The first optimal-exposure-period determiner may comprise: a first 
sub-determiner for determining a first effective maximum level value from 
a first further-provisional series of monochromatic image-pixel signals, 
which is further provisionally sensed from the recorded color image, with 
the image-sensor, by exposing the image sensor to the first monochromatic 
light rays over a first exposure period; and a second sub-determiner for 
determining a second effective maximum level-value from a second 
further-provisional series of monochromatic image-pixel signals, which is 
further provisionally sensed from the recorded color image, with the 
image-sensor, by exposing the image sensor to the first monochromatic 
light rays over a second exposure period, which is longer than the first 
exposure period. In this case, the first exposure period and the second 
exposure period are encompassed within the partial linear section of the 
characteristic curve, thereby determining the first optimal exposure 
period from a proportional calculation based on the first effective 
maximum level-value corresponding to the first exposure period, the second 
effective maximum level-value corresponding to the second exposure period, 
and an effective maximum level-value corresponding to the first optimal 
exposure period. 
The second optimal-exposure-period determiner may comprise: a first 
sub-determiner for determining a first effective maximum level value from 
a first further-provisional series of monochromatic image-pixel signals, 
which is sensed from the recorded color image, with the image-sensor, by 
exposing the image sensor to the second monochromatic light rays over a 
first exposure period; and a second sub-determiner for determining a 
second effective maximum level-value from a second further-provisional 
series of monochromatic image-pixel signals, which is sensed from the 
recorded color image, with the image-sensor, by exposing the image sensor 
to the second monochromatic light rays over a second exposure period, 
which is longer than the first exposure period. In this case, the first 
exposure period and the second exposure period are encompassed within the 
partial linear section of the characteristic curve, thereby determining 
the second optimal exposure period from a proportional calculation based 
on the first effective maximum level-value corresponding to the first 
exposure period, the second effective maximum level-value corresponding to 
the second exposure period, and an effective maximum level-value 
corresponding to the second optimal exposure period.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 schematically shows an embodiment of a color-image reader according 
to the present invention, which is constituted so as to read a recorded 
negative color image from a transparency film. Note, in FIG. 1, the 
transparency film is indicated by reference M, and the transparency film M 
is held by a frame holder F. 
The color-image reader comprises a plate-like carriage 10 on which the 
frame holder F is detachably mounted. Namely, the carriage 10 is provided 
with a pair of spring fasteners 12 attached thereto, by which the frame 
holder F is releasably fastened onto the carriage 10. Although not visible 
in FIG. 1, a rectangular opening is formed in the carriage 10, the opening 
being large enough to encompass the transparency film M. 
The plate-like carriage 10 is movable in the directions indicated by an 
open arrow shown in FIG. 1, and the movement of the carriage 10 is carried 
out by a suitable drive motor 14, such as a stepping motor, a servo motor 
or the like. Namely, the drive motor 14 has a pinion 16, fixedly mounted 
on an output shaft thereof, which is meshed with a rack 18 formed on a 
longer side of the carriage 10. 
The color-image reader also comprises a light source 20, which includes an 
elongated frame member 22 having red-light emitters 24R, green-light 
emitters 24G and blue-light emitters 24B supported thereby. Although only 
six light emitters (24R, 24G, 24B) are representatively shown in FIG. 1, 
in actuality, a plurality of red-light emitters 24R, a plurality of 
green-light emitters 24G and a plurality of blue-light emitters 24B are 
held in the elongated frame member 22 and are alternately arranged 
uniformly therealong. Each of the light emitters may comprise a light 
emitting diode (LED) emitting a predetermined monochromatic light (red, 
green or blue). 
As shown in FIG. 1, the light source 20 is arranged transversely above a 
path along which the carriage 10, and therefore the transparency film M, 
is moved. The plurality of red-light emitters 24R, the plurality of 
green-light emitters 24G, and the plurality of blue-light emitters 24B are 
cyclically turned ON in a predetermined order. For example, in succession, 
the red-light emitters 24R are turned ON, emitting red-light rays, then 
the green-light emitters 24G are turned ON, emitting green-light rays, and 
finally the blue-light emitters 24B are turned ON, emitting blue-light 
rays. Namely, the emissions of the three-primary colors of light from the 
light source 20 are cyclically repeated in the order of: the red-light 
emission, the green-light emission and the blue-light emission. 
The color-image reader further comprises a cylindrical condenser lens 26, 
interposed between the light source 20 and the path of the transparency 
film M. The monochromatic light rays (red, green or blue), emitted from 
the light source 20, are condensed by the cylindrical condenser lens 26 
and are directed in parallel toward the transparency film M. 
Furthermore, the color-image reader comprises a one-dimensional CCD line 
image sensor 28, and a focusing lens system 30 associated therewith. The 
CCD line image sensor 28 is arranged transversely below the path of the 
transparency film M, and is aligned with the optical axes of the elongated 
light source 20. In this embodiment, the focusing lens system 30 is formed 
as a rod lens array, and is interposed between the CCD line image sensor 
28 and the path of the transparency film M. Due to the focusing lens 
system 30, the monochromatic light rays, passing through the transparency 
film M, are focused onto a linear light-receiving surface of the CCD line 
image sensor 28. 
The CCD line image sensor 28 includes a plurality of CCD elements aligned 
with each other, and the linear light-receiving surface is formed by the 
alignment of the CCD elements. Each of the CCD elements generates and 
accumulates electric charge in accordance with an amount of light rays 
received thereby, and a degree of accumulation of electric charge in each 
CCD element depends on a time of exposure of the CCD elements of the CCD 
line image sensor 28 to the light rays. The CCD line image sensor 28 is 
provided with an electronic shutter function, by which the time of 
exposure, i.e. a time of electric-charge-accumulation, is regulated, as 
stated hereinafter in detail. 
FIG. 2 schematically shows a block diagram of the color-image reader shown 
in FIG. 1. The color-image reader is provided with a system control 
circuit 32, which may be constituted as a microcomputer comprising a 
central processing unit (CPU), a read-only memory (ROM) for storing 
programs, constants, etc, and a random access memory (RAM) for storing 
temporary data. 
As shown in FIG. 2, the drive motor 14 is connected to the system control 
circuit 32, through a driver circuit 34, and is driven on the basis of a 
series of drive pulses outputted from the driver circuit 34, which is 
operated by the system control circuit 32. During a reading operation of 
the color-image reader, the drive motor 14 is intermittently driven in 
such a manner that the plate-like carriage 10, and therefore the 
transparency film M, is intermittently moved to pass between the 
cylindrical condenser lens 26 and the focusing lens system 30, whereby the 
transparency film M is scanned in a step-by-step manner with the CCD line 
image sensor 28. 
The LED's 24R, 24G and 24B of the light source 20 are connected to the 
system control circuit 32, via an LED driver circuit 36, and are 
electrically powered by the LED driver circuit 36, which is operated by 
the system control circuit 32. In this embodiment, the red LED's 24R, the 
green LED's 24G and the blue LED's 24B are cyclically and successively 
turned ON as mentioned previously. Namely, the emissions of the primary 
colors of light from the light source 20 are cyclically repeated, for 
example, in the order of the red-light emission, the green-light emission 
and the blue-light emission during the intermittent stoppage of the 
carriage 10. In particular, the transparency film M is subjected to one 
cycle of the successive emissions of the primary colors of light during 
each standstill of the transparency film M when being intermittently 
moved. 
The CCD line image sensor 28 is connected to the system control circuit 32, 
through a CCD driver circuit 38, and is then driven by the CCD driver 
circuit 38. When the transparency film M is illuminated with the 
monochromatic light rays (red, green, blue) of the colored light emitters, 
the monochromatic light rays concerned, having passed through the 
cylindrical condenser lens 26 and the transparency film M, are focused, by 
the focusing lens system 30, onto the linear light-receiving surface of 
the CCD line image sensor 28. During the illumination of the transparency 
film M with the monochromatic light lays concerned, the electronic shutter 
of the CCD line image sensor 28 is opened by the CCD driver circuit 38 
under control of the system control circuit 32, so that electrical charges 
are started to be generated and accumulated in the CCD elements of the CCD 
line image sensor 28. 
Also, the accumulated electrical charges are outputted as a single-line of 
monochromatic image-pixel signals, from the CCD line image sensor 28, by 
driving the CCD driver circuit 38 under control of the system control 
circuit 32. The single-line of monochromatic image-pixel signals, 
outputted from the CCD line image sensor 28, is amplified by an amplifier 
40, and is then converted into a single-line of digital monochromatic 
image-pixel signals by an analog-to-digital (A/D) converter 42. Note, the 
amplifier 40 and the A/D converter 42 are operated under control of the 
system control circuit 32. 
The single-line of digital monochromatic image-pixel signals, outputted 
from the A/D converter 42, is inputted to an image-signal processing 
circuit 44, in which the single-line of digital monochromatic image-pixel 
signals is subjected to various processes, such as a shading-correction, a 
gamma correction, a white balance correction and so on. 
In particular, as shown in FIG. 3, the image-signal processing circuit 44 
includes three look-up tables (LUT) 44R, 44G and 44B. A single-line of 
digital red image-pixel signals, a single-line of digital green 
image-pixel signals and a single-line of digital blue image-pixel signals, 
which are successively outputted from the A/D converter 42, are inputted 
to the LUT's 44R, 44G and 44B, respectively, and are subjected to the 
shading-correction, gamma correction, white balance correction and so on. 
Namely, the single-line of digital monochromatic image-pixel signals, 
inputted to the corresponding LUT (44R, 44G, 44B), is outputted as a 
single-line of processed or corrected digital monochromatic image-pixel 
signals therefrom, and is then stored in a memory 46. 
When the sensing or reading of the recorded color image of the transparency 
film M, i.e. a scanning operation of the transparency film M with the CCD 
line image sensor 28, is completed, the memory 46 stores three frames of 
primary-color digital image-pixel signals: a frame of red digital 
image-pixel signals, a frame of green digital image-pixel signals and a 
frame of blue digital image-pixel signals. 
Thereafter, the three frames of primary-color digital image-pixel signals 
are read out from the memory 46 under control of the system control 
circuit 32, and are then transferred to a peripheral image processing 
computer (not shown), through the intermediary of an interface circuit 48 
and a terminal connector 50. In particular, when an 
image-data-transferring command signal is outputted from the peripheral 
image processing computer to the color-image reader, the three frames of 
primary-color digital image-pixel signals are read out, from the memory 
46, and are subjected to a format-conversion processing and so on in the 
interface circuit 48. Then, the transfer of the three frames of 
primary-color digital image-pixel signals from the color-image reader to 
the peripheral image processing computer is carried out through the 
terminal connector 50. 
Note, in FIG. 2, reference 52 indicates a switch panel on which switches 
for directly executing various operations of the color-image reader are 
provided. 
As discussed hereinbefore, during the sensing and reading of the recorded 
image from the recording medium, a time of exposure, over a period of 
which the CCD line image sensor 28 is exposed to the light rays, should be 
optimally and accurately regulated before the sensed and read image can be 
obtained with an ideal contrast. 
For a better understanding of the principle of the present invention for 
determining the optimal exposure time, a conventional method of 
determining the optimal exposure time will now be explained below. 
Note, the conventional determination of the optimal exposure time can be 
executed in the color-image reader as shown in FIGS. 1 and 2, when 
necessary. 
Prior to a regular reading-operation of a recorded image from the 
transparency film M, a pre-reading operation is executed to obtain a frame 
of digital image-pixel signals, which is temporarily stored in the memory 
46. In the pre-reading operation, a time of exposure, which is relatively 
shorter than a time of exposure in the regular reading-operation, is 
selected. Note, the pre-reading operation may be executed with a rougher 
scan-pitch than that used in the regular reading-operation. 
Then, as shown in FIG. 4, a histogram Ho is produced on the basis of the 
frame of digital image-pixel signals, and is temporarily stored in the 
memory 46. As is well known, in the histogram H.sub.0 of FIG. 4, the 
abscissa represents a level-value of the digital image-pixel signals 
included in one frame, and the ordinate represents a number of digital 
image-pixels having the same level-value. For example, when an analog 
image-pixel signal is converted into a 10-bit digital image-pixel signal 
by the A/D converter 42, each of the digital image-pixel signals included 
in one frame is classified into any one of 1,024 level-values. 
Subsequently, an effective maximum level-value of the histogram H.sub.0 is 
determined. In FIG. 4, the effective maximum level-value of the histogram 
H.sub.0 is indicated by reference L.sub.0, and may be defined as a 
boundary-level-value of a hatched area HA.sub.0, including an 
actual-maximum level-value, of the histogram H.sub.0, in which a number of 
digital image-pixel signals, corresponding to 0.5% of the total number of 
the digital image-pixel signals in one frame, for example, is included. 
Note, the digital image-pixel signals, included in the hatched area 
HA.sub.0, are derived from the highest-transparency area of the recorded 
image of the transparency film M. 
FIG. 5 is a graph conceptually illustrating how the optimal exposure time 
is determined in accordance with the conventional method. In this graph, 
the abscissa represents a time of electric-charge-accumulation, i.e. a 
time of exposure, over a period of which a specific CCD element of the CCD 
line image sensor 28 is exposed to the monochromatic light rays (red, 
green, blue), passing through the highest-transparency area of the 
recorded image of the transparency film M, and the ordinate represents a 
degree of electric charge, which is generated and accumulated in a 
specific CCD element of the CCD line image sensor 28. 
Namely, a characteristic curve, shown in the graph of FIG. 5, represents a 
change in the degree of electric charge accumulation in the specific CCD 
element of the CCD line image sensor 28, while the specific CCD element of 
the CCD line image sensor 28 is exposed to the monochromatic light rays 
(red, green, blue), passing through the highest-transparency area of the 
recorded image of the transparency film M. As is apparent from the 
characteristic curve, as the time of exposure increases, the degree of 
electric charge accumulation in the specific CCD element of the CCD line 
image sensor 28 gradually increases, and finally becomes saturated with 
the generated electric charges. 
In the graph of FIG. 5, reference to indicates an exposure period, over 
which the CCD line image sensor 28 is exposed to the monochromatic light 
rays at each of the scan-steps while the pre-reading operation is 
executed, and reference D.sub.0 indicates a degree of electric charge 
accumulation, which is obtained at the time when the exposure period 
t.sub.0 is completed. Accordingly, the degree of electric charge 
accumulation D.sub.0 corresponds to the effective maximum level-value 
L.sub.0 (FIG. 4). 
In the graph of FIG. 5, the optimal exposure period, indicated by reference 
T.sub.OPT, is determined such that a maximum degree of electric charge 
accumulation D.sub.MAX is obtained at the time when a period of the 
optimum exposure period T.sub.OPT is completed. Note, the maximum degree 
of electric charge accumulation D.sub.MAX is suitably predetermined in 
view of a dynamic range of the A/D converter 42 during manufacture of the 
color-image reader, and an effective maximum level-value, corresponding to 
the maximum degree of electric charge accumulation D.sub.MAX, is thus 
indicated by reference L.sub.MAX in FIG. 4. 
In accordance with the conventional determination method, an improper 
exposure period T.sub.ERR (FIG. 5) is calculated as the optimal exposure 
period T.sub.OPT, because the calculation is based on an erroneous 
assumption that the characteristic curve of FIG. 5 exhibits a linear 
function. Namely, in the conventional determination method, it is assumed 
that the following formula can be approximately established: 
EQU T.sub.OPT .apprxeq.(L.sub.MAX /L)*t 
However, in reality, the improper exposure period T.sub.ERR, which 
seriously diverges from the optimal exposure period T.sub.OPT, merely 
obtained using the following directly proportional calculation: 
EQU T.sub.ERR =(L.sub.MAX /L)*t 
According to a principle of the present invention for determining the 
optimal exposure period, prior to a regular reading-operation of a 
recorded image from the transparency film M, a first pre-reading operation 
and a second pre-reading operation are executed to obtain a first frame of 
digital image-pixel signals and a second frame of digital image-pixel 
signals, respectively, which are stored in the memory 46. In the first and 
second pre-reading operations, a first exposure period and a second 
exposure period are set, respectively. The first exposure period is 
shorter than a time of exposure to be set in the regular 
reading-operation. Also, the second exposure period is longer than the 
first exposure period, but is shorter than the time of exposure to be set 
in the regular reading-operation. 
Note, the first and second pre-reading operations also may be executed with 
rougher scan-pitches than that of the regular reading-operation. 
Then, as shown in FIG. 6, two histograms H.sub.1 and H.sub.2 are produced 
on the basis of the first frame of digital image-pixel signals and the 
second frame of digital image-pixel signals, respectively, and are stored 
in the memory 46. As mentioned above, since an analog image-pixel signal 
is converted into a 10-bit digital image-pixel signal by the A/D converter 
42, each of the digital image-pixel signals included in each frame are 
classified into any one of 1,024 level-values. 
Subsequently, a first effective maximum level-value of the digital 
image-pixel signals included in the first frame is determined from the 
first histogram H.sub.1, and a second effective maximum level-value of the 
digital image-pixel signals included in the second frame is determined 
from the second histogram H.sub.2. In FIG. 6, the respective first and 
second effective maximum level-values are indicated by references L.sub.1 
and L.sub.2, and each effective maximum level-value (L.sub.1, L.sub.2) may 
be defined as a boundary-level-value of a corresponding hatched area 
(HA.sub.1, HA.sub.2), including an actual-maximum level-value, of the 
histogram (H.sub.1, H.sub.2), in which a number of digital image-pixel 
signals, corresponding to 0.5% of the total number of the digital 
image-pixel signals in each frame, for example, is included. Note, similar 
to the above-mentioned case, the digital image-pixel signals, included in 
each hatched area (HA.sub.1, HA.sub.2), are derived from the 
highest-transparency area of the recorded image of the transparency film 
M. 
FIG. 7 is a graph conceptually illustrating how the optimal exposure period 
is determined in accordance with the principle of the present invention. 
This graph is essentially identical to the graph of FIG. 5. Namely, a 
characteristic curve, shown in the graph of FIG. 7, represents a change in 
the degree of electric charge accumulation in the specific CCD element of 
the CCD line image sensor 28, which is exposed to the monochromatic light 
rays (red, green, blue), passing through the highest-transparency area of 
the recorded image of the transparency film M. 
In the graph of FIG. 7, the respective first and second exposure periods, 
which are set in the first and second pre-reading operations, are 
indicated by references t.sub.1 and t.sub.2. As is apparent from FIG. 7, 
the settings of the first and second exposure periods t.sub.1 and t.sub.2 
are performed so that these exposure periods t.sub.1 and t.sub.2 are 
encompassed within a linear section of the characteristic curve, even 
though the characteristic curve may be shifted along the abscissa, due to 
a change in transparency of a recorded image due to a reading of another 
transparent film. 
Similar to the above-mentioned case, a degree of electric charge 
accumulation D.sub.1, which is obtained at the time when the exposure 
period t.sub.1 is completed, corresponds to the first effective maximum 
level-value L.sub.1 (FIG. 6), and a degree of electric charge accumulation 
D.sub.2, which is obtained at the time when the exposure period t.sub.2 is 
completed, corresponds to the second effective maximum level-value L.sub.2 
(FIG. 6) 
In the graph of FIG. 7, the optimal exposure period T.sub.OPT can be 
accurately determined on the basis of the following proportional 
calculation: 
EQU (L.sub.MAX -L.sub.1)/(T.sub.OPT -t.sub.1)=(L.sub.2 -L.sub.1)/(t.sub.2 
-t.sub.1) 
Namely, this formula can be rearranged as follows: 
EQU T.sub.OPT =[(L.sub.MAX -L.sub.1)/(L.sub.2 -L.sub.1)]*(t.sub.2 
-t.sub.1)+t.sub.1 
In this rearrangement, the term "[(L.sub.MAX -L.sub.1)/(L.sub.2 
-L.sub.1)]*(t.sub.2 -t.sub.1)" accurately represents the difference 
(T.sub.OPT -t.sub.1), due to the linear section of the characteristic 
curve of FIG. 7. Thus, the determination of the optimal exposure period 
T.sub.OPT can be accurately achieved by adding the period t.sub.1 to the 
term 
EQU "[(L.sub.MAX -L.sub.1)/(L.sub.2 -L.sub.1)]*(t.sub.2 -t.sub.1)". 
FIGS. 8 and 9 show a flowchart of a determination routine for determining 
an optimal exposure period, executed in the color-image reader according 
to the present invention. The execution is started by turning ON a first 
determination-start switch provided on the switch panel 52 after a power 
ON/OFF switch (not shown) of the color-image reader has been turned ON. 
Each of FIGS. 10 and 11 shows a timing chart for assisting in an 
explanation of the determination routine of FIGS. 8 and 9. 
At step 801, the drive motor 14 is driven to move the carriage 10, and the 
transparency film M, toward a scan-start position. At step 802, the memory 
46 is cleared, and, at step 803, a counter Y is reset. Note, the counter Y 
counts a number of scanning-steps or moving-steps of the transparency film 
M, during a pre-reading operation of a recorded image of the transparency 
film M. 
At step 804, it is monitored whether the transparency film M, held by the 
frame holder F, has reached a scan-start position. When it is confirmed 
that the transparency film M has reached the scan-start position, the 
control proceeds to step 805, in which the driving of the drive motor 14 
is stopped. 
At step 806, the plurality of red LED's 24R is powered ON, and the CCD line 
image sensor 28 is illuminated by the red-light rays, passing through the 
transparency film M, carrying red-image information. During the 
illumination of the CCD line image sensor 28 by the red-light rays, the 
CCD elements of the CCD line image sensor 28 are exposed to the red-light 
rays over a first exposure period t.sub.1(R), which corresponds to the 
first exposure period t.sub.1 shown in the graph of FIG. 7, and then a 
single-line of red image-pixel signals R1.sub.Y is read from the CCD line 
image sensor 28, as shown in the timing chart of FIG. 10. The read 
image-pixel signals R1.sub.Y are successively converted into digital red 
image-pixel signals by the A/D converter 42, and the single-line of 
digital red image-pixel signals (R1.sub.Y) is then stored in the memory 
46. 
In particular, after the powering-ON of the red LED's 24R, a shutter-gate 
signal is turned ON at a given timing, as shown in the timing chart of 
FIG. 10, whereby the electronic shutter of the CCD line image sensor 28 is 
opened, enabling the exposure of the CCD elements of the CCD line image 
sensor 28 to the red-light rays to be started. Namely, as soon as the 
shutter-gate signal is turned ON, an electric charge is generated and 
accumulated as a red image-pixel signal in each of the CCD elements of the 
CCD line image sensor 28. 
Then, when a read-out-gate signal is turned ON, as shown in the timing 
chart of FIG. 10, the single-line of red image-pixel signals R1.sub.Y is 
shifted from the CCD elements of the CCD line image sensor 28 to a 
transfer CCD path thereof. As is apparent from the timing chart of FIG. 
10, when the read-out-gate signal is turned OFF, i.e. when the shifting of 
the single-line of red image-pixel signals R1.sub.Y from the CCD elements 
to the transfer CCD path thereof is completed, the first exposure period 
t.sub.1(R) ends. Just after the read-out-gate signal is turned OFF, the 
shutter-gate signal is also turned OFF, and thus residual electric charges 
are drained out from all of the CCD elements of the CCD line image sensor 
28. 
On the other hand, the shifted red image-pixel signals R1.sub.Y are read 
out from the CCD line image sensor 28, and are amplified by the amplifier 
40. Then, the amplified red image-pixel signals are successively converted 
into digital red image-pixel signals by the A/D converter 42, and stored 
in the memory 46 as the single-line of digital red image-pixel signals 
(R1.sub.Y), as already mentioned above. 
At step 807, a histogram-production routine, as shown in FIG. 12, is 
executed to partially produce a first red-histogram (H.sub.1(R) in FIG. 
13), corresponding to the first histogram H.sub.1 of FIG. 6, on the basis 
of the single-line of digital red image-pixel signals (R1.sub.Y). 
At step 808, the plurality of green LED's 24G is powered ON, and the CCD 
line image sensor 28 is illuminated by the green-light rays, passing 
through the transparency film M, carrying green-image information. During 
the illumination of the CCD line image sensor 28 by the green-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
green-light rays over a first exposure period t.sub.1(G), which 
corresponds to the first exposure period t.sub.1 shown in the graph of 
FIG. 7, and then a single-line of green image-pixel signals G1.sub.Y is 
read from the CCD line image sensor 28, as shown in the timing chart of 
FIG. 10. The read image-pixel signals G1.sub.Y are successively converted 
into digital green image-pixel signals by the A/D converter 42, and the 
single-line of digital green image-pixel signals (G1.sub.Y) is then stored 
in the memory 46. 
Note, the first exposure period t.sub.1(G) is regulated in substantially 
the same manner as the first exposure period t.sub.1(R), and the reading 
of the single-line of green image-pixel signals G1.sub.Y is performed in 
substantially the same manner as the reading of the single-line of red 
image-pixel signals R1.sub.Y. 
At step 809, the histogram-production routine, as shown in FIG. 12, is also 
executed to partially produce a first green-histogram (H.sub.1(G) in FIG. 
13), corresponding to the first histogram H.sub.1 of FIG. 6, on the basis 
of the single-line of digital green image-pixel signals (G1.sub.Y). 
At step 810, the plurality of blue LED's 24B is powered ON, and the CCD 
line image sensor 28 is illuminated by the blue-light rays, passing 
through the transparency film M, carrying blue-image information. During 
the illumination of the CCD line image sensor 28 by the blue-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
blue-light rays over a first exposure period t.sub.1(B), which corresponds 
to the first exposure period t.sub.1 shown in the graph of FIG. 7, and 
then a single-line of blue image-pixel signals B1.sub.Y is read from the 
CCD line image sensor 28, as shown in the timing chart of FIG. 10. The 
read image-pixel signals B1.sub.Y are successively converted into digital 
blue image-pixel signals by the A/D converter 42, and the single-line of 
digital blue image-pixel signals (B1.sub.Y) is then stored in the memory 
46. 
Note, the first exposure period t.sub.1(B) is also regulated in 
substantially the same manner as the first exposure period t.sub.1(R), and 
the reading of the single-line of blue image-pixel signals B1.sub.Y is 
also performed in substantially the same manner as the reading of the 
single-line of red image-pixel signals R1.sub.Y. 
At step 811, the histogram-production routine, as shown in FIG. 12, is 
further executed to partially produce a first blue-histogram (H.sub.1(B) 
in FIG. 13), corresponding to the first histogram H.sub.1 of FIG. 6, on 
the basis of the single-line of digital blue image-pixel signals 
(B1.sub.Y). 
At step 812, the plurality of red LED's 24R is again powered ON, and the 
CCD line image sensor 28 is illuminated by the red-light rays, passing 
through the transparency film M, carrying red-image information. During 
the illumination of the CCD line image sensor 28 by the red-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
red-light rays over a second exposure period t.sub.2(R), which corresponds 
to the second exposure period t.sub.2 shown in the graph of FIG. 7, and 
then a single-line of red image-pixel signals R2.sub.Y is read from the 
CCD line image sensor 28, as shown in the timing chart of FIG. 11. The 
read image-pixel signals R2.sub.Y are successively converted into digital 
red image-pixel signals by the A/D converter 42, and the single-line of 
digital red image-pixel signals (R2.sub.Y) is then stored in the memory 
46. 
In particular, after the powering-ON of the red LED's 24R, the shutter-gate 
signal is turned ON at a given timing, as shown in the timing chart of 
FIG. 11, whereby the electronic shutter of the CCD line image sensor 28 is 
opened, enabling the exposure of the CCD elements of the CCD line image 
sensor 28 to the red-light rays to be started. Namely, as soon as the 
shutter-gate signal is turned ON, an electric charge is generated and 
accumulated as a red image-pixel signal in each of the CCD elements of the 
CCD line image sensor 28. 
Then, when a read-out-gate signal is turned ON, as shown in the timing 
chart of FIG. 11, the single-line of red image-pixel signals R2.sub.Y is 
shifted from the CCD elements of the CCD line image sensor 28 to the 
transfer CCD path thereof. As is apparent from the timing chart of FIG. 
11, when the read-out-gate signal is turned OFF, i.e. when the shifting of 
the single-line of red image-pixel signals R2.sub.Y from the CCD elements 
to the transfer CCD path thereof is completed, the second exposure period 
t.sub.2(R) ends. Just after the read-out-gate signal is turned OFF, the 
shutter-gate signal is also turned OFF, and thus residual electric charges 
are drained out from all of the CCD elements of the CCD line image sensor 
28. 
On the other hand, the shifted red image-pixel signals R2.sub.Y are read 
out from the CCD line image sensor 28, and are amplified by the amplifier 
40. Then, the amplified red image-pixel signals are successively converted 
into digital red image-pixel signals by the A/D converter 42, and stored 
in the memory 46 as the single-line of digital red image-pixel signals 
(R2.sub.Y), as already mentioned above. 
At step 813, the histogram-production routine, as shown in FIG. 12, is 
executed to partially produce a second red-histogram (H.sub.2(R) in FIG. 
13), corresponding to the second histogram H.sub.2 of FIG. 6, on the basis 
of the single-line of digital red image-pixel signals (R2.sub.Y). 
At step 814, the plurality of green LED's 24G is again powered ON, and the 
CCD line image sensor 28 is illuminated by the green-light rays, passing 
through the transparency film M, carrying green-image information. During 
the illumination of the CCD line image sensor 28 by the green-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
green-light rays over a second exposure period t.sub.2(G), which 
corresponds to the second exposure period t.sub.2 shown in the graph of 
FIG. 7, and then a single-line of green image-pixel signals G2.sub.Y is 
read from the CCD line image sensor 28, as shown in the timing chart of 
FIG. 11. The read image-pixel signals G2.sub.Y are successively converted 
into digital green image-pixel signals by the A/D converter 42, and the 
single-line of digital green image-pixel signals (G2.sub.Y) is then stored 
in the memory 46. 
Note, the second exposure period t.sub.2(G) is regulated in substantially 
the same manner as the second exposure period t.sub.2(R), and the reading 
of the single-line of green image-pixel signals G2.sub.Y is performed in 
substantially the same manner as the reading of the single-line of red 
image-pixel signals R2.sub.Y. 
At step 815, the histogram-production routine, as shown in FIG. 12, is 
again executed to partially produce a second green-histogram (H.sub.2(G) 
in FIG. 13), corresponding to the second histogram H.sub.2 of FIG. 6, on 
the basis of the single-line of digital green image-pixel signals 
(G2.sub.Y). 
At step 816, the plurality of blue LED's 24B is powered ON, and the CCD 
line image sensor 28 is illuminated by the blue-light rays, passing 
through the transparency film M, carrying blue-image information. During 
the illumination of the CCD line image sensor 28 by the blue-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
blue-light rays over a second exposure period t.sub.2(B), which 
corresponds to the second exposure period t.sub.2 shown in the graph of 
FIG. 7, and then a single-line of blue image-pixel signals B2.sub.Y is 
read from the CCD line image sensor 28, as shown in the timing chart of 
FIG. 11. The read image-pixel signals B2.sub.Y are successively converted 
into digital blue image-pixel signals by the A/D converter 42, and the 
single-line of digital blue image-pixel signals (B2.sub.Y) is then stored 
in the memory 46. 
Note, the second exposure period t.sub.2(B) is also regulated in 
substantially the same manner as the second exposure period t.sub.2(R), 
and the reading of the single-line of blue image-pixel signals B2.sub.Y is 
also performed in substantially the same manner as the reading of the 
single-line of red image-pixel signals R2.sub.Y, 
At step 817, the histogram-production routine, as shown in FIG. 12, is 
further executed to partially produce a second blue-histogram (H2.sub.(B) 
in FIG. 13), corresponding to the second histogram H.sub.2 of FIG. 6, on 
the basis of the single-line of digital blue image-pixel signals 
(B2.sub.Y). 
At step 818, the drive motor 14 is driven to advance the carriage 10, and 
therefore the transparency film M, by one scan-step. Then, at step 819, 
the counter Y is incremented by one, and the control proceeds to step 820, 
in which it is determined whether a count number of the counter Y has 
reached TY. Note, TY represents a total number of scan-steps which is 
necessary for completely reading the recorded image of the transparency 
film M in the pre-reading operation, and the total scan-steps TY may be 
previously set and stored in the ROM of the system control circuit 32. 
If Y&lt;TY, the control returns from step 820 to step 806, and the routine 
comprising steps 806 to 820 is repeatedly executed until the count number 
of the counter Y reaches TY. At step 820, when the count number of the 
counter Y has reached TY, i.e. when the pre-reading operation is 
completed, the control proceeds from step 820 to step 821. 
Note, at this stage, the production of the first and second red-histograms 
(H.sub.1(R) and H.sub.2(R)) based on all of the single-lines of the 
digital red image-pixel signals R1.sub.Y and R2.sub.Y, the production of 
the first and second green-histograms (H.sub.1(G) and H.sub.2(G)) based on 
all of the single-lines of digital green image-pixel signals G1.sub.Y and 
G2.sub.Y, and the production of the first and second blue-histograms 
(H.sub.1(B) and H.sub.2(B)) based on all of the single-lines of digital 
blue image-pixel signals B1.sub.Y and B2.sub.Y have been completed. 
At step 821, an effective maximum level-value determination routine, as 
shown in FIGS. 14 to 16, is executed, whereby an effective maximum 
level-value is determined from each of the above-mentioned histograms. 
Namely, respective effective maximum level-values L.sub.1(R), L.sub.1(G) 
and L.sub.1(B), each of which corresponds to L.sub.1 of FIG. 6, are 
obtained from the first red-histogram (H.sub.1(R)), first green-histogram 
(H.sub.1(G)) and first blue-histogram (H.sub.1(B)), and respective 
effective maximum level-values L.sub.2(R), L.sub.2(G) and L.sub.2(B), each 
of which corresponds to L.sub.2 of FIG. 6, are obtained from the second 
red-histogram (H.sub.2(R)), second green-histogram (H.sub.2(G)) and second 
blue-histogram (H.sub.2(B)). 
Then, at step 822, optimal exposure periods T.sub.OPT(R), T.sub.OPT(G) and 
T.sub.OPT(B) are calculated from the following formulas: 
EQU T.sub.OPT(R) .rarw.[(L.sub.MAX(R) +L.sub.1(R))/(L.sub.2(R) 
-L.sub.1(R))]*(t.sub.2(R) -t.sub.1(R))+t.sub.1(R) 
EQU T.sub.OPT(G) .rarw.[(L.sub.MAX(G) +L.sub.1(G))/(L.sub.2(G) 
-L.sub.1(G))]*(t.sub.2(G) -t.sub.1(G))+t.sub.1(G) 
EQU T.sub.OPT(B) .rarw.[(L.sub.MAX(B) +L.sub.1(B))/(L.sub.2(B) -L.sub.1(B)) 
]*(t.sub.2(B) -t.sub.1(B))+t.sub.1(B) 
Herein: Each of L.sub.MAX(R), L.sub.MAX (G) and L.sub.MAX(B) corresponds to 
L.sub.MAX of FIG. 6. 
Note, L.sub.MAX(R), L.sub.MAX(G) and L.sub.MAX(B) are suitably 
predetermined in view of the dynamic range of the A/D converter 42, and 
may be previously stored in the ROM of the system control circuit 32. 
The calculated results, i.e. the optimal exposure periods T.sub.OPT(R), 
T.sub.OPT(G) and T.sub.OPT(B), are stored in the RAM of the system control 
circuit 32, and are used when a pre-reading operation for determinating 
color-correction parameters, as explained hereinafter, and a regular 
reading operation are executed in the color-image reader. 
With reference to FIG. 12, the histogram-production routine, executed in 
each of steps 807, 809, 811, 813, 815 and 817 of the flowchart of FIGS. 8 
and 9, will now be explained below. 
Prior to the explanation of the histogram-production routine, the following 
matters are confirmed for assisting in the explanation: 
1) A single-line of monochromatic (red, green, blue) image-pixel signals, 
read from the CCD line image sensor 28, is converted into a single-line of 
digital monochromatic image-pixel signals by the A/D converter 42, and 
these digital monochromatic image-pixel signals included in one 
single-line are stored in the memory 46. 
2) Each of the digital monochromatic image-pixel signals is classified into 
any one of the 1,024 level-values due to the conversion of the analog 
image-pixel signal into the 10-bit digital image-pixel signal by the A/D 
converter 42, as already mentioned above. 
3) As conceptually shown in FIG. 13, the first red-histogram, indicated by 
reference H.sub.1(R), is stored in areas defined by addresses "0000" to 
"1023" of the memory 46; 
the first green-histogram, indicated by reference H.sub.1(G), is stored in 
areas defined by addresses "1024" to "2047" of the memory 46; 
the first blue-histogram, indicated by reference H.sub.1(B), is stored in 
areas defined by addresses "2048" to "3071" of the memory 46; 
the second red-histogram, indicated by reference H.sub.2(R), is stored in 
areas defined by addresses "3072" to "4095" of the memory 46; 
the second green-histogram, indicated by reference H.sub.2(G), is stored in 
areas defined by addresses "4096" to "5119" of the memory 46; and 
the second blue-histogram, indicated by reference H.sub.2(B), is stored in 
areas defined by addresses "5120" to "6143" of the memory 46. 
4) A histogram-production counter R.sub.1 K[L] is defined in each of the 
addresses "0000" to "1023", and is used to count a number of digital red 
image-pixel signals having the same level-value L; 
a histogram-production counter G.sub.1 K[L] is defined in each of the 
addresses "1024" to "2047", and is used to count a number of digital green 
image-pixel signals having the same level-value L; 
a histogram-production counter B.sub.1 K[L] is defined in each of the 
addresses "2048" to "3071", and is used to count a number of digital blue 
image-pixel signals having the same level-value L; 
a histogram-production counter R.sub.2 K[L] is defined in each of the 
addresses "3072" to "4095", and is used to count a number of digital red 
image-pixel signals having the same level-value L; 
a histogram-production counter G.sub.2 K[L] is defined in each of the 
addresses "4096" to "5119", and is used to count a number of digital green 
image-pixel signals having the same level-value L; and 
a histogram-production counter B.sub.2 K[L] is defined in each of the 
addresses "5120" to "6143", and is used to count a number of digital blue 
image-pixel signals having the same level-value L. 
5) A level-value L of a digital monochromatic image-pixel signal is 
represented by any one of [L=0000] to [L=1023]. 
At step 1201, a counter X is reset. The counter X is used to count a number 
of the digital monochromatic image-pixel signals (red, green, blue) 
included in one single-line. Then, at step 1202, a level-value L is 
detected with respect to one (L.sub.X) of the digital monochromatic 
image-pixel signals included in one single-line. Note, the level-value L 
represents one of the 1,024 level-values. 
At step 1203, a count number of a histogram-production counter CK[L], 
representing any one of R.sub.1 K[L], G.sub.1 K[L], B.sub.1 K[L], R.sub.2 
K[L], G.sub.2 K[L] and B.sub.2 K[L], is incremented by one. Then, at step 
1204, the count number of the counter X is incremented by one. 
Subsequently, at step 1205, it is determined whether the count number of 
the counter X has reached TX. Note, "TX" represents a total number of the 
digital monochromatic image-pixel signals included in one single-line, 
which is equal to the total number of the CCD elements of the CCD line 
image sensor 28, and which may be previously set and stored in the ROM of 
the system control circuit 32. 
If X&lt;TX, the control returns from step 1205 to step 1202, and the routine 
comprising steps 1202 to 1205 is repeatedly executed until the count 
number of the counter X reaches TX. At step 1205, when the count number of 
the counter X has reached TX, i.e. when a partial production of a 
histogram based on the single-line of the digital monochromatic 
image-pixel signals is completed, the control returns to one of steps 807, 
809, 811, 813, 815 and 817 of the flowchart of FIGS. 8 and 9. 
With reference to FIGS. 14 to 16, the effective maximum level-value 
determination routine, executed in step 821 of the flowchart of FIGS. 8 
and 9, will now be explained below. 
At step 1401, a level-value L, representing any one of [0000] to [1023], is 
set to the maximum level-value [1023], and, at step 1402, an 
image-pixel-signal-number parameter SN, representing a number of digital 
monochromatic image-pixel signals, is initialized as 0. 
At step 1403, a threshold value TH is set by the following calculation: 
EQU TH.rarw.0.005*TN 
Herein, TN indicates a total number of digital monochromatic image-pixel 
signals included in one frame. Namely, a number of digital monochromatic 
image-pixel signals, corresponding to 0.5% of the total number TN of the 
digital monochromatic image-pixel signals in one frame, is set as the 
threshold value TH. 
At step 1404, the following calculation is executed: 
EQU SN.rarw.SN+R.sub.1 K[L=1023] 
Then, at step 1405, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 1405 to step 1406, in which the 
level-value L is decremented by one. Then, at step 1407, it is determined 
whether the level value L is greater than or equal to the minimum 
level-value [0000]. At this stage, since L=1023, the control returns from 
step 1407 to step 1404. Namely, the routine comprising steps 1404 to 1407 
is repeatedly executed until the image-pixel-signal-number parameter SN 
reaches or exceeds the threshold value TH. 
At step 1405, when SN.gtoreq.TH, the control proceeds from step 1405 to 
step 1409, in which the level-value L, obtained at this stage, is stored, 
as the effective maximum level-value L.sub.1(R) of the first red-histogram 
H.sub.1(R), in the RAM of the system control circuit 32. 
On the other hand, at step 1407, if it is determined that the level-value L 
is less than the minimum level-value [0000] during the execution of the 
routine comprising steps 1404 to 1407, without the 
image-pixel-signal-number parameter SN reaching or exceeding the threshold 
value TH, the first red-histogram H.sub.1(R) has been abnormally produced. 
In this case, the control proceeds from step 1407 to step 1408, in which 
an error message, announcing that the pre-reading operation should be 
repeated, is displayed on, for example, an LCD (liquid crystal display) 
panel (not shown ) provided on the color-image reader. 
At step 1410, the level-value L is again set to be the maximum level-value 
[1023], and, at step 1411, the image-pixel-signal-number parameter SN is 
reset to 0. 
At step 1412, the following calculation is executed: 
EQU SN.rarw.SN+G.sub.1 K[L=1023] 
Then, at step 1413, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 1413 to step 1414, in which the 
level-value L is decremented by one. Then, at step 1415, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1023, the control returns from step 1415 to 
step 1412. Namely, the routine comprising steps 1412 to 1415 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 1413, if SN.gtoreq.TH, the control proceeds from step 1413 to step 
1417, in which the level-value L, obtained at this stage, is stored, as 
the effective maximum level-value L.sub.1(G) of the first green-histogram 
H.sub.1(G), in the RAM of the system control circuit 32. 
Similar to the above mentioned case, at step 1415, if it is determined that 
the level-value L is less than zero during the execution of the routine 
comprising steps 1412 to 1415, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the first 
green-histogram H.sub.1(G) has been abnormally produced. Accordingly, the 
control proceeds from step 1415 to step 1416, in which the error message, 
announcing that the pre-reading operation should be repeated, is displayed 
on the LCD panel of the color-image reader. 
At step 1418, the level-value L is again set to the maximum level-value 
[1023], and, at step 1419, the image-pixel-signal-number parameter SN is 
again reset to 0. 
At step 1420, the following calculation is executed: 
EQU SN.rarw.SN+B.sub.1 K[L=1023] 
Then, at step 1421, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 1421 to step 1422, in which the 
level-value L is decremented by one. Then, at step 1423, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1023, the control returns from step 1423 to 
step 1420. Namely, the routine comprising steps 1420 to 1423 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 1421, if SN.gtoreq.TH, the control proceeds from step 1421 to step 
1425, in which the level-value L, obtained at this stage, is stored, as 
the effective maximum level-value L.sub.1(B) of the first blue-histogram 
H.sub.1(B), in the RAM of the system control circuit 32. 
However, at step 1423, if it is determined that the level-value L is less 
than the minimum level-value [0000] during the execution of the routine 
comprising steps 1420 to 1423, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the first 
blue-histogram H.sub.1(B) has been abnormally produced. Accordingly, the 
control proceeds from step 1423 to step 1424, in which the error message, 
announcing that the pre-reading operation should be repeated, is displayed 
on the LCD panel of the color-image reader. 
At step 1426, the level-value L is set to the maximum level-value [1023], 
and, at step 1427, the image-pixel-signal-number parameter SN is 
initialized as 0. 
At step 1428, the following calculation is executed: 
EQU SN .rarw.SN+R.sub.2 K[L=1023] 
Then, at step 1429, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 1429 to step 1430, in which the 
level-value L is decremented by one. Then, at step 1431, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1023, the control returns from step 1431 to 
step 1428. Namely, the routine comprising steps 1428 to 1431 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 1429, if SN.gtoreq.TH, the control proceeds from step 1429 to step 
1433, in which the level-value L, obtained at this stage, is stored, as 
the effective maximum level-value L.sub.2(R) of the second red-histogram 
H.sub.2(R), in the RAM of the system control circuit 32. 
However, at step 1431, if it is determined that the level-value L is less 
than the minimum level-value [0000] during the execution of the routine 
comprising steps 1428 to 1431, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the second 
red-histogram L.sub.2(R) has been abnormally produced. Accordingly, the 
control proceeds from step 1431 to step 1432, in which the error message, 
announcing that the pre-reading operation should be repeated, is displayed 
on the LCD panel of the color-image reader. 
At step 1434, the level-value L is reset to the maximum level-value [1023], 
and, at step 1435, the image-pixel-signal-number parameter SN is again 
initialized as 0. 
At step 1436, the following calculation is executed: 
EQU SN.rarw.SN+G.sub.2 K[L=1023] 
Then, at step 1437, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 1437 to step 1438, in which the 
level-value L is decremented by one. Then, at step 1439, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1023, the control returns from step 1439 to 
step 1436. Namely, the routine comprising steps 1436 to 1439 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 1437, if SN.gtoreq.TH, the control proceeds from step 1437 to step 
1441, in which the level-value L, obtained at this stage, is stored, as 
the effective maximum level-value L.sub.2(G) of the second green-histogram 
H.sub.2(G), in the RAM of the system control circuit 32. 
However, at step 1439, if it is determined that the level-value L is less 
than the minimum level-value [0000] during the execution of the routine 
comprising steps 1436 to 1439, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the second 
green-histogram H.sub.2(G) has been abnormally produced. Accordingly, the 
control proceeds from step 1439 to step 1440, in which the error message, 
announcing that the pre-reading operation should be repeated, is displayed 
on the LCD panel of the color-image reader. 
At step 1442, the level-value L is set to the maximum level-value [1023], 
and, at step 1443, the image-pixel-signal-number parameter SN is 
initialized as 0. 
At step 1444, the following calculation is executed: 
EQU SN.rarw.SN+B.sub.2 K[L=1023] 
Then, at step 1445, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 1445 to step 1446, in which the 
level-value L is decremented by one. Then, at step 1447, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1023, the control returns from step 1447 to 
step 1444. Namely, the routine comprising steps 1444 to 1447 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 1445, if SN.gtoreq.TH, the control proceeds from step 1445 to step 
1449, in which the level-value L, obtained at this stage, is stored, as 
the effective maximum level-value L.sub.2(B) of the second blue-histogram 
H.sub.2(B), in the RAM of the system control circuit 32. 
However, at step 1447, if it is determined that the level-value L is less 
than the minimum level-value [0000] during the execution of the routine 
comprising steps 1444 to 1447, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the second 
blue-histogram H.sub.2(B) has been abnormally produced. Accordingly, the 
control proceeds from step 1447 to step 1448, in which the error message, 
announcing that the pre-reading operation should be repeated, is displayed 
on the LCD panel of the color-image reader. 
After the determination of the effective maximum level-values L.sub.1(R), 
L.sub.(G), L.sub.1(B), L.sub.2(R), L.sub.2(G) and L.sub.2(B) is completed, 
the control returns to step 822 of the flowchart of FIGS. 8 and 9, in 
which the exposure periods T.sub.OPT(R), T.sub.OPT(G) and T.sub.OPT(B) are 
calculated as mentioned above. 
FIGS. 17 to 19 show graphs conceptually illustrating how three frames of 
read monochromatic (red, green, blue) image-pixel signals are processed to 
obtain the best color balance in accordance with the present invention. 
After the determination of the optimal exposure periods T.sub.OPT(R), 
T.sub.OPT(G) and T.sub.OPT(B), a further pre-reading operation is executed 
to determine color-correction parameters for the color-correction, prior 
to a regular reading-operation of the recorded image from the transparency 
film M. Namely, in this further pre-reading operation, a frame of red 
image-pixel signals, a frame of green image-pixel signals, and a frame of 
blue image-pixel signals, derived from the optimal exposure periods 
T.sub.OPT(R), T.sub.OPT(G) and T.sub.OPT(B), respectively, are obtained. 
Then, three respective histograms are produced on the basis of the frame 
of red image-pixel signals, the frame of green image-pixel signals, and 
the frame of blue image-pixel signals. With reference to FIG. 17, the 
above-mentioned three histograms are represented by a conceptual histogram 
H.sub.C1. 
Note, the pre-reading operation for determining the color-correction 
parameters also may be executed with a rougher scan-pitch than that used 
in the regular reading-operation. 
Subsequently, an effective minimum level-value HL.sub.MIN and an effective 
maximum level-value HL.sub.MAX are determined from the histogram H.sub.C1. 
The effective minimum level-value HL.sub.MIN may be defined as a 
boundary-level-value of a hatched area HA.sub.LL, including an 
actual-minimum level-value, of the histogram H.sub.C1, in which a number 
of digital image-pixel signals, corresponding to 0.5% of the total number 
of the digital image-pixel signals in one frame, for example, is included. 
The effective maximum level-value H.sub.MAX may be defined as a 
boundary-level-value of a hatched area HA.sub.HL, including an 
actual-maximum level-value, of the histogram H.sub.C1, in which a number 
of digital image-pixel signals, corresponding to 0.5% of the total number 
of the digital image-pixel signals in one frame, for example, is included. 
Note, of course, the digital image-pixel signals, included in the hatched 
area HA.sub.LL, are derived from the lowest-transparency area of the 
recorded image of the transparency film M, and the digital image-pixel 
signals, included in the hatched area HA.sub.HL, are derived from the 
highest-transparency area of the recorded image of the transparency film 
M. 
Also, in FIG. 17, respective references M.sub.MIN and M.sub.MAX indicate a 
minimum level-value and a maximum level-value, which may be defined by an 
input-range of the look-up tables (LUT) 44R, 44G and 44B of the 
image-signal processing circuit 44. Namely, the minimum level-value 
coincides with a minimum level-value of an image-pixel signal, which is 
allowed to be inputted to the LUT (44R, 44G, 44B), and the maximum 
level-value M.sub.MAX coincides with a maximum level-value of an 
image-pixel signal, which is allowed to be inputted to the LUT (44R, 44G, 
44B). Note, although the minimum level-value M.sub.MIN and the maximum 
level-value are commonly set with respect to the LUT 44R, 44G and 44B, 
respective minimum level-values and respective maximum level-values may be 
individually set with respect to the LUT's 44R, 44G and 44B, if necessary. 
In principle, the color balance is carried out among the three frames of 
monochromatic (red, green, blue) image-pixel signals as follows: 
First, the histogram H.sub.C1 is shifted along the abscissa of the graph of 
FIG. 17, until the effective minimum level-value HL.sub.MIN coincides with 
the minimum level-value M.sub.MIN, as shown in a graph of FIG. 18. Namely, 
in this graph, the shifted histogram is indicated by reference H.sub.C2. 
The shifting of the histogram is achieved by converting a level-value 
L.sub.i each of the image-pixel signals included in one frame, on the 
basis of the following formula: 
EQU CL1.sub.i =(L.sub.i -HL.sub.MIN)+M.sub.MIN 
Herein: CL1.sub.i indicates a converted level-value. 
Then, the shifted histogram H.sub.C2 is expanded such that the effective 
maximum level-value HL.sub.MAX coincides with the maximum level-value 
M.sub.MAX, as shown in a graph of FIG. 19. Namely, in this graph, the 
expanded histogram is indicated by reference H.sub.C3 The expansion of the 
histogram is achieved by further converting a level-value CL1.sub.i of 
each of the image-pixel signals, on the basis of the following formula: 
EQU CL2.sub.i =CL1.sub.i *[(M.sub.MAX -M.sub.MIN)/(HL.sub.MAX -HL.sub.MIN)] 
Herein: CL2.sub.i indicates a further converted level-value. 
In short, a red histogram, a green histogram and a blue histogram are 
individually processed to be subjected to the above-mentioned 
conversion-processes, whereby a color balance can be carried out among the 
three frames of monochromatic (red, green, blue) image-pixel signals. 
Note, in actuality, the above-mentioned conversion-processes are all at 
once achieved on the basis of the following formula: 
EQU CL2.sub.i =(L.sub.i -HL.sub.MIN)*[(M.sub.MAX -M.sub.MIN)/(HL.sub.MAX 
-HL.sub.MIN)]+M.sub.MIN 
Namely, the effective minimum level-value HL.sub.MIN and the coefficient 
"(M.sub.MAX -M.sub.MIN)/(HL.sub.MAX -HL.sub.MIN)" are utilized as 
color-correction parameters in a regular reading-operation of the recorded 
color image from the transparency film M. 
In this embodiment, since the transparency film M is a negative 
transparency film, the negative color image may be converted into a 
positive color image, if necessary. The conversion of the negative color 
image into the positive color image is carried out on the basis of the 
following formula: 
EQU PL.sub.i =M.sub.MAX -CL2.sub.i +M.sub.MIN 
Herein: PL.sub.i indicates a level-value of an image-pixel signal subjected 
to the negative-to-positive conversion process. 
Referring to FIG. 20, a histogram, which is produced on the basis of the 
frame of monochromatic positive image-pixel signals subjected to the 
negative-to-positive conversion process, is indicated by reference 
H.sub.C4. 
The frame of monochromatic positive image-pixel signals is then inputted to 
the corresponding LUT (44R, 44G, 44B) of the image-signal processing 
circuit 44, and is processed to be subjected to the shading-correction, 
gamma correction, white balance correction and so on. With reference to 
FIG. 21, a histogram, which is produced on the basis of the frame of 
monochromatic positive image-pixel signals processed in the image-signal 
processing circuit 44, is indicated by reference H.sub.C5. 
Note, as can be easily understood, if the transparency film M is a positive 
transparency film, the positive color image can be converted into the 
negative color image. In this case, the conversion of the positive color 
image into the positive color image is carried out on the basis of the 
same formula "P1.sub.i =M.sub.MAX -CL2.sub.i +M.sub.MIN " as mentioned 
above. 
FIGS. 22 and 23 show a flowchart of a color-correction parameter 
determination routine for determining color-correction parameters, 
executed in the color-image reader according to the present invention. The 
execution is started by turning ON a second determination-start switch 
provided on the switch panel 52. FIG. 24 shows a timing chart for 
assisting in an explanation of the color-correction parameter 
determination routine of FIGS. 22 and 23. 
At step 2201, the drive motor 14 is driven to move the carriage 10, and the 
transparency film M, toward a scan-start position. At step 2202, the 
memory 46 is cleared, and, at step 2203, a counter Y is reset. Note, the 
counter Y counts a number of scanning-steps or moving-steps of the 
transparency film M, during a pre-reading operation of a recorded image of 
the transparency film M. 
At step 2204, it is monitored whether the transparency film M, held by the 
frame holder F, has reached a scan-start position. When it is confirmed 
that the transparency film M has reached the scan-start position, the 
control proceeds to step 2205, in which the driving of the drive motor 14 
is stopped. 
At step 2206, the plurality of red LED's 24R is powered ON, and the CCD 
line image sensor 28 is illuminated by the red-light rays, passing through 
the transparency film M, carrying red-image information. During the 
illumination of the CCD line image sensor 28 by the red-light rays, the 
CCD elements of the CCD line image sensor 28 are exposed to the red-light 
rays over the optimal exposure period T.sub.OPT(R), and then a single-line 
of red image-pixel signals R.sub.Y is read from the CCD line image sensor 
28, as shown in the timing chart of FIG. 24. The read image-pixel signals 
R.sub.Y are successively converted into digital red image-pixel signals by 
the A/D converter 42, and the single-line of digital red image-pixel 
signals (R.sub.Y)is then stored in the memory 46. 
At step 2207, the histogram-production routine, as shown in FIG. 12, is 
executed to partially produce a red-histogram (H.sub.C1(R) in FIG. 25), 
corresponding to the histogram H.sub.C1 of FIG. 17, on the basis of the 
single-line of digital red image-pixel signals (R.sub.Y). 
At step 2208, the plurality of green LED's 24G is powered ON, and the CCD 
line image sensor 28 is illuminated by the green-light rays, passing 
through the transparency film M, carrying green-image information. During 
the illumination of the CCD line image sensor 28 by the green-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
green-light rays over the optimal exposure period T.sub.OPT(G), and then a 
single-line of green image-pixel signals G.sub.Y is read from the CCD line 
image sensor 28, as shown in the timing chart of FIG. 24. The read 
image-pixel signals G.sub.Y are successively converted into digital green 
image-pixel signals by the A/D converter 42, and the single-line of 
digital green image-pixel signals (G.sub.Y) is then stored in the memory 
46. 
At step 2209, the histogram-production routine, as shown in FIG. 12, is 
executed to partially produce a green-histogram (H.sub.C1(G) in FIG. 25), 
corresponding to the histogram H.sub.C1 of FIG. 17, on the basis of the 
single-line of digital red image-pixel signals (G.sub.Y). 
At step 2210, the plurality of blue LED's 24B is powered ON, and the CCD 
line image sensor 28 is illuminated by the blue-light rays, passing 
through the transparency film M, carrying blue-image information. During 
the illumination of the CCD line image sensor 28 by the blue-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
blue-light rays over the optimal exposure period T.sub.OPT(B), and then a 
single-line of blue image-pixel signals B.sub.Y is read from the CCD line 
image sensor 28, as shown in the timing chart of FIG. 24. The read 
image-pixel signals B.sub.Y are successively converted into digital blue 
image-pixel signals by the A/D converter 42, and the single-line of 
digital blue image-pixel signals (B.sub.Y) is then stored in the memory 
46. 
At step 2211, the histogram-production routine, as shown in FIG. 12, is 
further executed to partially produce a blue-histogram (H.sub.C1(B) in 
FIG. 25), corresponding to the histogram H.sub.C1 of FIG. 17, on the basis 
of the single-line of digital blue image-pixel signals (B.sub.Y). 
Note, the regulation of the optimal exposure periods (T.sub.OPT(R), 
T.sub.OPT(G), T.sub.OPT(B)) and the reading of the image-pixel signals 
(R.sub.Y, G.sub.Y, B.sub.Y) from the CCD image sensor 28 are carried out 
in substantially the same manner as in the optimal exposure period 
determination routine of FIGS. 8 and 9. 
At step 2212, the drive motor 14 is driven to advance the carriage 10, and 
therefore the transparency film M, by one scan-step. Then, at step 2213, 
the counter Y is incremented by one, and the control proceeds to step 
2214, in which it is determined whether a count number of the counter Y 
has reached TY. Note, "TY" represents a total number of scan-steps which 
is necessary for completely reading the recorded image of the transparency 
film M in the pre-reading operation, and the total scan-steps TY may be 
previously set and stored in the ROM of the system control circuit 32. 
If Y&lt;TY, the control returns from step 2214 to step 2206, and the routine 
comprising steps 2206 to 2214 is repeatedly executed until the count 
number of the counter Y reaches TY. At step 2214, when the count number of 
the counter Y has reached TY, i.e. when the pre-reading operation is 
completed, the control proceeds to step 2215. 
Note, at this stage, the production of the red-histogram (H.sub.C1(R)) 
based on all of the single-lines of the digital red image-pixel signals 
R.sub.Y, the production of the green-histogram (H.sub.C1(G)) based on all 
of the single-lines of digital green image-pixel signals G.sub.Y, and the 
production of the blue-histogram (H.sub.C1(B)) based on all of the 
single-lines of digital blue image-pixel signals B.sub.Y have been 
completed, and these monochromatic histograms (H.sub.C1(R), H.sub.C1(G) 
and H.sub.C1(B)) are stored in the memory 46, as conceptually shown in 
FIG. 25, in a similar fashion as previously described with respect to FIG. 
13. Namely, "RK[L]" indicates a histogram-production counter defined in 
each of the addresses "0000" to "1023" of the memory 46, and is used to 
count a number of digital red image-pixel signals having the same 
level-value L; "GK[L]" indicates a histogram-production counter defined in 
each of the addresses "1024" to "2047", and is used to count a number of 
digital green image-pixel signals having the same level-value L; and 
"BK[L]" indicates a histogram-production counter defined in each of the 
addresses "2048" to "3071", and is used to count a number of digital blue 
image-pixel signals having the same level-value L. 
At step 2215, an effective minimum level-value determination routine, as 
shown in FIGS. 26 and 27, is executed, whereby an effective minimum 
level-value is determined from each of the above-mentioned histograms. 
Namely, effective minimum level-values HL.sub.MIN(R), HL.sub.MIN(G) and 
HL.sub.MIN(B), each of which corresponds to HL.sub.MIN of FIG. 17, are 
obtained from the red-histogram H.sub.C1(R), green-histogram H.sub.C1(G) 
and blue-histogram H.sub.C1(B), respectively. Note, the effective minimum 
level-value determination routine is explained in detail hereinafter with 
reference to FIGS. 26 and 27. 
At step 2216, each of the respective effective minimum level-values 
(HL.sub.MIN(R), HL.sub.MIN(G) and HL.sub.MIN(B)) is stored as a first 
color-correction parameter (CP1.sub.(R) CP1.sub.(G), CP1.sub.(B)) in the 
RAM of the system control circuit 32. 
At step 2217, an effective maximum level-value determination routine, as 
shown in FIGS. 28 and 29, is executed, whereby an effective maximum 
level-value is determined from each of the above-mentioned histograms. 
Namely, effective maximum level-values H.sub.MAX(R), HL.sub.(G) and 
HL.sub.MAX(B), each of which corresponds to HL.sub.MAX of FIG. 17, are 
obtained from the red-histogram H.sub.C1(R), green-histogram H.sub.C1(G) 
and blue-histogram H.sub.C1(B), respectively. Note, the effective maximum 
level-value determination routine is explained in detail hereinafter with 
reference to FIGS. 28 and 29. 
At step 2218, the following calculations are executed: 
EQU CP2.sub.(R) .rarw.(M.sub.MAX -M.sub.MIN)/(HL.sub.MAX(R) -HL.sub.MIN(R)) 
EQU CP2.sub.(G) .rarw.(M.sub.MAX -M.sub.MIN)/(HL.sub.MAX(G) -HL.sub.MIN(G)) 
EQU CP2.sub.(R) .rarw.(M.sub.MAX -M.sub.MIN)/(HL.sub.MAX(B) -HL.sub.MIN(B)) 
Namely, each of the calculated results (CP2.sub.(R), CP2.sub.(G) and 
CP2.sub.B)) is stored as a second color-correction parameter in the RAM of 
the system control circuit 32. 
Note, as mentioned above, the respective minimum level-values M.sub.MIN(R), 
M.sub.MIN(G) and M.sub.MIN(B) and the respective maximum level-values 
M.sub.MAX(R), M.sub.MAX(G) and M.sub.MAX(B) may be suitably pre-determined 
in view of the critical minimum and maximum limits of the input ranges of 
the LUT's 44R, 44G and 44B of the image-signal processing circuit 44, and 
may be previously stored in the ROM of the system control circuit 32. 
The first color-correction parameters CP1.sub.(R), CP1.sub.(G) and 
CP1.sub.(B) and the second color-correction parameters CP2.sub.(R), 
CP2.sub.(G), CP2.sub.(B) are used in a regular reading operation executed 
in the color-image reader. 
With reference to FIGS. 26 to 27, the effective minimum level-value 
determination routine, executed in step 2215 of the flowchart of FIGS. 22 
and 23, will now be explained below. 
At step 2601, a level-value L, representing any one of [0000] to [1023], is 
set to the minimum level-value [0000], and, at step 2602, an 
image-pixel-signal-number parameter SN, representing a number of digital 
monochromatic (red, green, blue) image-pixel signals, is initialized as 0. 
At step 2603, a threshold value TH is set by the following calculation: 
EQU TH.rarw.0.005*TN 
Herein, TN indicates a total number of digital monochromatic image-pixel 
signals included in one frame. Namely, a number of digital monochromatic 
image-pixel signals, corresponding to 0.5% of the total number TN of the 
digital monochromatic image-pixel signals in one frame, is set as the 
threshold value TH. 
At step 2604, the following calculation is executed: 
EQU SN.rarw.SN+RK[L=0000] 
Then, at step 2605, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 2605 to step 2606, in which the 
level-value L is incremented by one. Then, at step 2607, it is determined 
whether the level value L is smaller than or equal to the maximum 
level-value [1023]. At this stage, since L=0001, the control returns from 
step 2607 to step 2604. Namely, the routine comprising steps 2604 to 2607 
is repeatedly executed until the image-pixel-signal-number parameter SN 
reaches or exceeds the threshold value TH. 
At step 2605, when SN.gtoreq.TH, the control proceeds from step 2605 to 
step 2609, in which the level-value L, obtained at this stage, is stored, 
as the effective minimum level-value HL.sub.MIN(R) of the red-histogram 
H.sub.C1(R), in the RAM of the system control circuit 32. 
On the other hand, at step 2607, if it is determined that the level-value L 
is more than the maximum level-value [1023] during the execution of the 
routine comprising steps 2604 to 2607, without the 
image-pixel-signal-number parameter SN reaching or exceeding the threshold 
value TH, the red-histogram H.sub.C1(R) has been abnormally produced. In 
this case, the control proceeds from step 2607 to step 2608, in which an 
error message, announcing that the pre-reading operation for determining 
the color-correction parameters should be repeated, is displayed on, for 
example, the LCD panel (not shown) provided on the color-image reader. 
At step 2610, the level-value L is again set to be the minimum level-value 
[0000], and, at step 2611, the image-pixel-signal-number parameter SN is 
reset to 0. 
At step 2612, the following calculation is executed: 
EQU SN.rarw.SN+GK[L=0000] 
Then, at step 2613, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 2613 to step 2614, in which the 
level-value L is incremented by one. Then, at step 2615, it is determined 
whether the level value L is equal to or less than the maximum level-value 
[1023]. At this stage, since L=0001, the control returns from step 2615 to 
step 2612. Namely, the routine comprising steps 2612 to 2615 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 2613, if SN.gtoreq.TH, the control proceeds from step 2613 to step 
2617, in which the level-value L, obtained at this stage, is stored, as 
the effective minimum level-value HL.sub.MIN(G) of the green-histogram 
H.sub.C1(G), in the RAM of the system control circuit 32. 
Similar to the above mentioned case, at step 2615, if it is determined that 
the level-value L is more than the maximum level-value [1023] during the 
execution of the routine comprising steps 2612 to 2615, without the 
image-pixel-signal-number parameter SN reaching or exceeding the threshold 
value TH, the green-histogram H.sub.C1(G) has been abnormally produced. 
Accordingly, the control proceeds from step 2615 to step 2616, in 
which-the error message, announcing that the pre-reading operation for 
determining the color-correction parameters should be repeated, is 
displayed on the LCD panel of the color-image reader. 
At step 2618, the level-value L is again set to the minimum level-value 
[0000], and, at step 2619, the image-pixel-signal-number parameter SN is 
again reset to 0. 
At step 2620, the following calculation is executed: 
EQU SN.rarw.SN+BK[L=0000] 
Then, at step 2621, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 2621 to step 2622, in which the 
level-value L is incremented by one. Then, at step 2623, it is determined 
whether the level value L is equal to or less than the maximum level-value 
[1023]. At this stage, since L=0001, the control returns from step 2623 to 
step 2620. Namely, the routine comprising steps 2620 to 2623 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 2621, if SN.gtoreq.TH, the control proceeds from step 2621 to step 
2625, in which the level-value L, obtained at this stage, is stored, as 
the effective minimum level-value HL.sub.MIN(B) of the blue-histogram 
H.sub.C1(B), in the RAM of the system control circuit 32. 
However, at step 2623, if it is determined that the level-value L is more 
than the maximum level-value [1023] during the execution of the routine 
comprising steps 2620 to 2623, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the 
blue-histogram H.sub.C1(B) has been abnormally produced. Accordingly, the 
control proceeds from step 2623 to step 2624, in which the error message, 
announcing that the pre-reading operation for determining the 
color-correction parameters should be repeated, is displayed on the LCD 
panel of the color-image reader. 
After the determination of the effective minimum level-values 
HL.sub.MIN(R), HL.sub.MIN(G) and HL.sub.MIN(B) is completed, the control 
returns to step 2216 of the flowchart of FIGS. 22 and 23. 
With reference to FIGS. 28 to 29, the effective maximum level-value 
determination routine, executed in step 2217 of the flowchart of FIGS. 22 
and 23, will now be explained below. 
At step 2801, a level-value L, representing any one of level-values [0000] 
to [1023], is set to the maximum level-value [1023], and, at step 2802, an 
image-pixel-signal-number parameter SN, representing a number of digital 
monochromatic (red, green, blue) image-pixel signals, is initialized as 0. 
At step 2803, a threshold value TH is set by the following calculation: 
EQU TH.rarw.0.005*TN 
Herein, TN indicates a total number of digital monochromatic image-pixel 
signals included in one frame. Namely, a number of digital monochromatic 
image-pixel signals, corresponding to 0.5% of the total number TN of the 
digital monochromatic image-pixel signals in one frame, is set as the 
threshold value TH. 
At step 2804, the following calculation is executed: 
EQU SN.rarw.SN+RK[L=1023] 
Then, at step 2805, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 2805 to step 2806, in which the 
level-value L is decremented by one. Then, at step 2807, it is determined 
whether the level value L is smaller than or equal to the minimum 
level-value [0000]. At this stage, since L=1022, the control returns from 
step 2807 to step 2804. Namely, the routine comprising steps 2804 to 2807 
is repeatedly executed until the image-pixel-signal-number parameter SN 
reaches or exceeds the threshold value TH. 
At step 2805, when SN.gtoreq.TH, the control proceeds from step 2805 to 
step 2809, in which the level-value L, obtained at this stage, is stored, 
as the effective maximum level-value HL.sub.MAX(R) of the red-histogram 
H.sub.C1(R), in the RAM of the system control circuit 32. 
On the other hand, at step 2807, if it is determined that the level-value L 
is less than the minimum level-value [0000] during the execution of the 
routine comprising steps 2804 to 2807, without the 
image-pixel-signal-number parameter SN reaching or exceeding the threshold 
value TH, the red-histogram H.sub.C1(R) has been abnormally produced. In 
this case, the control proceeds from step 2807 to step 2808, in which an 
error message, announcing that the pre-reading operation for determining 
the color-correction parameters should be repeated, is displayed on, for 
example, the LCD panel (not shown) provided on the color-image reader. 
At step 2810, the level-value L is again set to be the maximum level-value 
[1023], and, at step 2811, the image-pixel-signal-number parameter SN is 
reset to 0. 
At step 2812, the following calculation is executed: 
EQU SN.rarw.SN+GK[L=1023] 
Then, at step 2813, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 2813 to step 2814, in which the 
level-value L is decremented by one. Then, at step 2815, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1022, the control returns from step 2815 to 
step 2812. Namely, the routine comprising steps 2812 to 2815 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 2813, if SN.gtoreq.TH, the control proceeds from step 2813 to step 
2817, in which the level-value L, obtained at this stage, is stored, as 
the effective minimum level-value HL.sub.MAX(G) of the green-histogram 
H.sub.C1(G), in the RAM of the system control circuit 32. 
Similar to the above mentioned case, at step 2815, if it is determined that 
the level-value L is less than the minimum level-value [0000] during the 
execution of the routine comprising steps 2812 to 2815, without the 
image-pixel-signal-number parameter SN reaching or exceeding the threshold 
value TH, the green-histogram H.sub.C1(G) has been abnormally produced. 
Accordingly, the control proceeds from step 2815 to step 2816, in which 
the error message, announcing that the pre-reading operation for 
determining the color-correction parameters should be repeated, is 
displayed on the LCD panel of the color-image reader. 
At step 2818, the level-value L is again set to the maximum level-value 
[1023], and, at step 2819, the image-pixel-signal-number parameter SN is 
again reset to 0. 
At step 2820, the following calculation is executed: 
EQU SN.rarw.SN+BK[L=1023] 
Then, at step 2821, it is determined whether the image-pixel-signal-number 
parameter SN is equal to or more than the threshold value TH. 
If SN&lt;TH, the control proceeds from step 2821 to step 2822, in which the 
level-value L is decremented by one. Then, at step 2823, it is determined 
whether the level value L is equal to or more than the minimum level-value 
[0000]. At this stage, since L=1022, the control returns from step 2823 to 
step 2820. Namely, the routine comprising steps 2820 to 2823 is repeatedly 
executed until the image-pixel-signal-number parameter SN reaches or 
exceeds the threshold value TH. 
At step 2821, if SN.gtoreq.TH, the control proceeds from step 2821 to step 
2825, in which the level-value L, obtained at this stage, is stored, as 
the effective minimum level-value HL.sub.MAX(B) of the blue-histogram 
H.sub.C1(B), in the RAM of the system control circuit 32. 
However, at step 2823, if it is determined that the level-value L is less 
than the minimum level-value [0000] during the execution of the routine 
comprising steps 2820 to 2823, without the image-pixel-signal-number 
parameter SN reaching or exceeding the threshold value TH, the 
blue-histogram H.sub.C1(B) has been abnormally produced. Accordingly, the 
control proceeds from step 2823 to step 2824, in which the error message, 
announcing that the pre-reading operation for determining the 
color-correction parameters should be repeated, is displayed on the LCD 
panel of the color-image reader. 
After the determination of the effective maximum level-values 
HL.sub.MAX(R), HL.sub.MAX(G) and HL.sub.MAX(B) is completed, the control 
returns to step 2218 of the flowchart of FIGS. 22 and 23. 
FIGS. 30, 31, 32 and 33 show a flowchart of a regular reading operation 
routine, executed in the color-image reader according to the present 
invention. The execution is started by turning ON a 
regular-reading-operation-start switch provided on the switch panel 52. 
FIG. 34 shows a timing chart for assisting in an explanation of the 
regular reading operation routine of FIGS. 30 to 33. 
At step 3001, the drive motor 14 is driven to move the carriage 10, and the 
transparency film M, toward a scan-start position. At step 3002, the 
memory 46 is cleared, and, at step 3003, a counter Y is reset. Note, the 
counter Y counts a number of scanning-steps or moving-steps of the 
transparency film M, during a regular reading operation of a recorded 
image of the transparency film M. 
At step 3004, it is monitored whether the transparency film M, held by the 
frame holder F, has reached a scan-start position. When it is confirmed 
that the transparency film M has reached the scan-start position, the 
control proceeds to step 3005, in which the driving of the drive motor 14 
is stopped. 
At step 3006, a counter i is reset. Note, the counter i counts a number of 
processed image-pixel signals. Then, at step 3007, the plurality of red 
LED's 24R is powered ON, and the CCD line image sensor 28 is illuminated 
by the red-light rays, passing through the transparency film M, carrying 
red-image information. During the illumination of the CCD line image 
sensor 28 by the red-light rays, the CCD elements of the CCD line image 
sensor 28 are exposed to the red-light rays over the optimal exposure 
period T.sub.OPT(R), and then a single-line of red image-pixel signals 
R.sub.Y is read from the CCD line image sensor 28, as shown in the timing 
chart of FIG. 34. Note, a level-value of each of the red image-pixel 
signals R.sub.Y, is indicated by reference RL.sub.i in FIG. 34. The read 
red image-pixel signals R.sub.Y are successively converted into digital 
red image-pixel signals by the A/D converter 42. 
At step 3008, the single-line of digital red image-pixel signals (R.sub.Y), 
outputted from the A/D converter 42, is temporarily stored in the RAM of 
the system control circuit 32. Then, at step 3009, the following 
calculation is executed: 
EQU RCL2.sub.i .rarw.(RL.sub.i -CP1.sub.(R))*CP2.sub.(R) +M.sub.MIN 
Namely, each red image-pixel signal (RL.sub.i) is subjected to the color 
balance process. 
At step 3010, each red image-pixel signal (RCL2.sub.i), subjected to the 
color balance process, is stored in the memory 46 via the LUT 44R of the 
image-signal processing circuit 44. Namely, each red image-pixel signal 
(RCL2.sub.i) is stored in the memory 46, after being further subjected to 
the shading-correction, gamma correction, white balance correction and so 
on. 
At step 3011, the counter i is incremented by one, and the control proceeds 
to step 3012, in which it is determined whether a count number of the 
counter i has reached TX. Note, as already mentioned above, "TX" 
represents the total number of the digital red image-pixel signals 
(RL.sub.i) included in one single-line. If i&lt;TX, the control returns from 
step 3012 to step 3007, and the routine comprising steps 3007 to 3012 is 
repeatedly executed until the count number of the counter i reaches TX. 
At step 3012, when the count number of the counter i has reached TX, i.e. 
when all of the digital red image-pixel signals (R.sub.Y) included in one 
single-line have been subjected to the color balance process, the control 
proceeds from step 3012 to step 3013, in which the counter i is reset. 
At step 3014, the plurality of green LED's 24G is powered ON, and the CCD 
line image sensor 28 is illuminated by the green-light rays, passing 
through the transparency film M, carrying green-image information. During 
the illumination of the CCD line image sensor 28 by the green-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
green-light rays over the optimal exposure period T.sub.OPT(G), and then a 
single-line of green image-pixel signals G.sub.Y is read from the CCD line 
image sensor 28, as shown in the timing chart of FIG. 34. Note, a 
level-value of each of the green image-pixel signals G.sub.Y, is indicated 
by reference GL.sub.1 in FIG. 34. The read green image-pixel signals 
G.sub.Y are successively converted into digital green image-pixel signals 
by the A/D converter 42. 
At step 3015, the single-line of digital green image-pixel signals 
(G.sub.Y), outputted from the A/D converter 42, is temporarily stored in 
the RAM of the system control circuit 32. Then, at step 3016, the 
following calculation is executed: 
EQU GCL2.sub.i .rarw.(GL.sub.i -CP1.sub.(G))*CP2.sub.(G) +M.sub.MIN 
Namely, each green image-pixel signal (GL.sub.i) is subjected to the color 
balance process. 
At step 3017, each green image-pixel signal (GCL2.sub.i), subjected to the 
color balance process, is stored in the memory 46 via the LUT 44G of the 
image-signal processing circuit 44. Namely, each green image-pixel signal 
(GCL2.sub.i) is stored in the memory 46, after being further subjected to 
the shading-correction, gamma correction, white balance correction and so 
on. 
At step 3018, the counter i is incremented by one, and the control proceeds 
to step 3019, in which it is determined whether a count number of the 
counter i has reached TX. If i&lt;TX, the control returns from step 3019 to 
step 3014, and the routine comprising steps 3014 to 3019 is repeatedly 
executed until the count number of the counter i reaches TX. 
At step 3019, when the count number of the counter i has reached TX, i.e. 
when all of the digital green image-pixel signals (G.sub.Y) included in 
one single-line have been subjected to the color balance process, the 
control proceeds from step 3019 to step 3020, in which the counter i is 
reset. 
At step 3021, the plurality of blue LED's 24B is powered ON, and the CCD 
line image sensor 28 is illuminated by the blue-light rays, passing 
through the transparency film M, carrying blue-image information. During 
the illumination of the CCD line image sensor 28 by the blue-light rays, 
the CCD elements of the CCD line image sensor 28 are exposed to the 
blue-light rays over the optimal exposure period T.sub.OPT(B), and then a 
single-line of blue image-pixel signals B.sub.Y is read from the CCD line 
image sensor 28, as shown in the timing chart of FIG. 34. Note, a 
level-value of each of the blue image-pixel signals B.sub.Y, is indicated 
by reference BL.sub.i in FIG. 34. The read blue image-pixel signals 
B.sub.Y are successively converted into digital blue image-pixel signals 
by the A/D converter 42. 
At step 3022, the single-line of digital blue image-pixel signals 
(B.sub.Y), outputted from the A/D converter 42, is temporarily stored in 
the RAM of the system control circuit 32. Then, at step 3023, the 
following calculation is executed: 
EQU BCL2.sub.i .rarw.(BL.sub.i -CP1.sub.(B))*CP2.sub.(B) +M.sub.MIN 
Namely, each blue image-pixel signal (BL.sub.i) is subjected to the color 
balance process. 
At step 3024, each blue image-pixel signal (BCL2.sub.i), subjected to the 
color balance process, is stored in the memory 46 via the LUT 44B of the 
image-signal processing circuit 44. Namely, each blue image-pixel signal 
(BCL2.sub.i) is stored in the memory 46, after being further subjected to 
the shading-correction, gamma correction, white balance correction and so 
on. 
At step 3025, the counter i is incremented by one, and the control proceeds 
to step 3026, in which it is determined whether a count number of the 
counter i has reached TX. If i&lt;TX, the control returns from step 3026 to 
step 3021, and the routine comprising steps 3021 to 3026 is repeatedly 
executed until the count number of the counter i reaches TX. 
At step 3026, when the count number of the counter i has reached TX, i.e. 
when all of the digital blue image-pixel signals (B.sub.Y) included in one 
single-line have been subjected to the color balance process, the control 
proceeds from step 3026 to step 3027, in which the drive motor 14 is 
driven to advance the carriage 10, and therefore the transparency film M, 
by one scan-step. 
Then, at step 3028, the counter Y is incremented by one, and the control 
proceeds to step 3029, in which it is determined whether a count number of 
the counter Y has reached TY'. Note, "TY'" represents a total number of 
scan-steps which is necessary for completely reading the recorded image of 
the transparency film M in the regular reading operation, and the total 
scan-steps TY' may be previously set and stored in the ROM of the system 
control circuit 32. Also, note, the total scan-steps TY' is larger than 
the total scan-steps TY used in the optimal exposure determination routine 
of FIGS. 8 and 9 and the color-correction parameter determination routine 
of FIGS. 22 and 23. 
If Y&lt;TY', the control returns from step 3029 to stop 3006, and the routine 
comprising steps 3006 to 3029 is repeatedly executed until the count 
number of the counter Y reaches TY'. At step 3029, when the count number 
of the counter Y has reached TY', i.e. when the regular reading operation 
is completed, the control proceeds from step 3029 to step 3030. 
Note, at this stage, a storage of the three frames of digital monochromatic 
image-pixel signals (RCL2.sub.i, GCL2.sub.i and BCL2.sub.i) in the memory 
46 is completed. Also, note, the regulation of the optimal exposure 
periods (T.sub.OPT(R), T.sub.OPT(G), T.sub.OPT(B), and the reading of the 
image-pixel signals (R.sub.Y, G.sub.Y, B.sub.Y) from the CCD image sensor 
28 are carried out in substantially the same manner as in the optimal 
exposure period determination routine of FIGS. 8 and 9. 
At step 3030, it is determined whether either of a negative-to-positive 
conversion or a positive-to-negative conversion should be executed. Note, 
a command signal for the negative-to-positive conversion or the 
positive-to-negative conversion may be inputted to the system control 
circuit 32 by operating a selective command switch provided on the switch 
panel 52. If there is no inputting of the command signal for either the 
negative-to-positive conversion or the positive-to-negative conversion, 
the regular reading operation immediately ends. 
On the other hand, if there is an inputting of the command signal for, for 
example, the negative-to-positive conversion, the control proceeds from 
step 3030 to step 3031, in which the counter i is reset. 
At step 3032, the following calculation is executed: 
EQU RPL.sub.i .rarw.M.sub.MAX -RCL2.sub.i +M.sub.MIN 
Namely, the digital image pixel signal RCL2.sub.i is retrieved from the 
memory 46 to the RAM of the system control circuit 32, and is subjected to 
the negative-to-positive conversion. Then, the converted digital image 
pixel signal RPL.sub.i is stored in the memory 46. 
At step 3033, the counter i is incremented by one, and the control proceeds 
to step 3034, in which it is determined whether a count number of the 
counter i has reached TP. Note, "TP" represents the total number of the 
digital red image-pixel signals (RCL2.sub.i) included in one frame. If 
i&lt;TP, the control returns from step 3034 to step 3032, and the routine 
comprising steps 3032 to 3034 is repeatedly executed until the count 
number of the counter i reaches TP. 
At step 3034, when the count number of the counter i has reached TP, i.e. 
when the negative-to-positive conversion of the digital red image-pixel 
signals (RCL2.sub.i) is completed, the control proceeds from step 3034 to 
step 3035, in which the counter i is reset. 
At step 3036, the following calculation is executed: 
EQU GPL.sub.i .rarw.M.sub.MAX -GCL2.sub. i+M.sub.MIN 
Namely, the digital image pixel signal GCL2.sub.i is retrieved from the 
memory 46 to the RAM of the system control circuit 32, and is subjected to 
the negative-to-positive conversion. Then, the converted digital image 
pixel signal GPL.sub.i is stored in the memory 46. 
At step 3037, the counter i is incremented by one, and the control proceeds 
to step 3038, in which it is determined whether a count number of the 
counter i has reached TP. If i&lt;TP, the control returns from step 3038 to 
step 3036, and the routine comprising steps 3036 to 3038 is repeatedly 
executed until the count number of the counter i reaches TP. 
At step 3038, when the count number of the counter i has reached TP, i.e. 
when the negative-to-positive conversion of the digital green image-pixel 
signals (GCL2.sub.i) is completed, the control proceeds from step 3038 to 
step 3039, in which the counter i is reset. 
At step 3040, the following calculation is executed: 
EQU BPL.sub.i .rarw.M.sub.MAX -BCL2.sub.i +M.sub.MIN 
Namely, the digital image pixel signal BCL2.sub.i is retrieved from the 
memory 46 to the RAM of the system control circuit 32, and is subjected to 
the negative-to-positive conversion. Then, the converted digital image 
pixel signal BPL.sub.i is stored in the memory 46. 
At step 3041, the counter i is incremented by one, and the control proceeds 
to step 3042, in which it is determined whether a count number of the 
counter i has reached TP. If i&lt;TP, the control returns from step 3042 to 
step 3040, and the routine comprising steps 3040 to 3042 is repeatedly 
executed until the count number of the counter i reaches TP. 
At step 3042, when the count number of the counter i has reached TP, i.e. 
when the negative-to-positive conversion of the digital blue image-pixel 
signals (BCL2.sub.i) is completed, this routine ends. 
The three frames of digital monochromatic negative image-pixel signals 
(RCL2.sub.i, GCL2.sub.i and BCL2.sub.i) or the three frames of digital 
monochromatic positive image-pixel signals (RPL.sub.i, GPL.sub.i and 
BPL.sub.i) are read from the memory 46, and are then transferred to a 
peripheral image processing computer (not shown), through the intermediary 
of the interface circuit 48 and the terminal connector 50. 
Note, of course, the positive-to-negative conversion can be executed in 
substantially the same manner as the above-mentioned negative-to-positive 
conversion. 
Finally, it will be understood by those skilled in the art that the 
foregoing description is of the preferred embodiments of the device and 
that various changes and modifications may be made to the present 
invention without departing from the spirit and scope thereof. 
The present disclosure relates to subject matter contained in Japanese 
Patent Application No. 9-176474 (filed on Jun. 17, 1997), which is 
expressly incorporated herein, by reference, in its entirety.