Image forming method for silver halide photographic material

A apparatus for forming an image on a silver halide photosensitive material with a plurality of recording elements aligned in the form of at least a single line, each recording element is driven so as to conduct an On-Off exposure independently to obtain a light amount datum in accordance with a density of a image signal, a correction value is calculated from the light amount datum and a light amount of each recording element is corrected with the correction value.

BACKGROUND OF THE INVENTION 
The present invention relates to an image forming method by which a 
continuous gradation recording is conducted on a silver halide 
photographic material. 
Conventionally, the importance of gradation is well known in order to 
reproduce a high quality image. Stating gradation more concretely, the 
continuity in continuous gradation, in particular, the reproduction of low 
density gradation in portions in which the density is almost uniform, such 
as the moderate gradation in the contrast in the skin of an enlarged human 
figure or in the sky is very important. In order to realize good gradation 
in a digital image, gradation control higher than at least 200 levels is 
requested. On the other hand, a technique to record a continuous gradation 
image with an array light source is well known. The array light source 
makes it possible to conduct image formation at high speed and at low cost 
with a small sized apparatus. 
For example, the following methods are well known. 
(1) A first method such as the Dither method with which a multi-gradation 
image is depicted in the pseudo sense by combining a plurality of binary 
pixels. 
(2) A second method with which the light intensity or the light emission 
time period per one time of each element in the array light source is 
changed independently in accordance with the gradation level. However, 
since the first method is a pseudo-depiction method in which the image 
resolution is sacrificed, it may be difficult to expect high resolution 
recording. With the second method, a D/A converter and a comparator are 
needed for each recording element, resulting in a driver circuit for the 
recording elements which becomes complicated and expensive. 
Then, a third method with which a multi-level recording is conducted by 
plural time exposures with the use of a binary or multi-level array light 
source may be considered. 
However, with the third method, good gradation may be obtained without 
degrading the resolution and without causing the apparatus to become 
complicated and expensive. On the other hand, in the condition that the 
gradation is enhanced, there may be a problem that density unevenness 
caused by the deviation among the light emission characteristics of each 
recording element becomes conspicuous. 
To overcome this problem, the following correction may be considered. That 
is, the recording elements are controlled sequentially one by one to emit 
light and the emitted light intensity of each element is measured, the 
correction value for the deviation among the light emission 
characteristics of each recording element is obtained on the basis of the 
measurement, and the correction is conducted on the basis of the 
correction value. For example, in the method disclosed in WO90/09890, 
since recording is conducted on a recording medium of a high contrast 
gradation characteristics, the gradation depiction is conducted basically 
only by area modulation, it may be difficult to obtain a sufficiently 
continuous gradation image. To counter this problem, a technique to 
improve the gradation continuity with the use of a line-formed light 
source element with which the recording width per one line is made small 
may be considered. However, on the other hand, it is difficult to obtain 
the maximum density due to the deficiency of the light amount, resulting 
in another problem being raised. Further, in the case of the application 
on a silver halide photosensitive material of the low contrast recording 
medium, the recording mode shows the density modulation and the continuous 
gradation is enhanced. However, since the density unevenness may not be 
eliminated appropriately, there may another problem in that the unevenness 
on the portion in which the density is almost an equal density which is 
especially important for the reproduction of the gradation becomes 
conspicuous in comparison with a complicated image portion. 
SUMMARY OF THE INVENTION 
The present invention has been conceived in light of the above problems. An 
objective is to provide an apparatus with which a continuous gradation 
image can be recorded with a high resolution without causing the apparatus 
to become complicate and a high cost and a high quality image in which 
density unevenness is not conspicuous can be formed on a silver halide 
photosensitive material. 
The above objective can be attained by the following methods and 
structures. 
In Method 1, in an image forming method in which a plurality of recording 
elements (or exposing elements) which are aligned in the form of a single 
line or plural lines and can be driven On-Off independently are driven 
On-Off plural times by the combination of the same or different time 
periods in accordance with image data so that exposure is conducted on a 
silver halide photosensitive material, light amount data are obtained for 
each recording element on the condition that plural pieces of the 
recording elements are being driven, and a correction value for an 
exposure amount of each recording element is obtained on the basis of the 
light amount data. 
In Structure 1, in an image forming apparatus in which a plurality of 
recording elements (exposing elements) which are aligned in the form of a 
single line or plural lines and can be driven On-Off independently are 
driven On-Off plural times by the combination of the same or different 
time periods in accordance with image data so that exposure is conducted 
on a silver halide photosensitive material, the apparatus comprises 
control means for obtaining light amount data for each recording element 
on the condition that plural pieces of the recording elements are being 
driven, for obtaining a correction value for an exposure amount of each 
recording element on the basis of the light amount data, and for 
correcting the recording elements on the basis of the correction value. 
With Method 1 and Structure 1, on the condition that a plurality of 
recording elements are driven in which the condition is close to an actual 
image recording condition, a light amount is obtained and the correction 
is conducted, whereby the density unevenness caused by the deviation of 
the light emission characteristics of each recording element can be 
reduced, a high resolution continuous gradation image can be obtained and 
a high quality image can be formed, without resulting in a complicated 
apparatus on high cost in comparison with cases where a light amount is 
measured and the correction is conducted on condition that each element is 
controlled to emit light one by one and in which the condition is 
different from the actual image recording condition. Incidentally, the 
plurality of recording elements arranged in the array form includes a 
staggered arrangement. 
In Method 2, in an image forming method in which a plurality of recording 
elements which are aligned in the form of a single line or plural lines 
and can be driven On-Off independently are driven On-Off a plural number 
of times by the combination of the same or different time periods in 
accordance with image data so that exposure is conducted on a silver 
halide photosensitive material, light amount data are obtained for each 
recording element on the condition that plural pieces of the same kind of 
recording elements of the recording element to be obtained the light 
amount are being driven, and a correction value for an exposure amount of 
each recording element is obtained on the basis of the light amount data. 
Further, in Structure 2, in an image forming apparatus in which a 
plurality of recording elements which are aligned in the form of a single 
line or plural lines and can be driven On-Off independently is driven 
On-Off a plural number of times by the combination of the same or 
different time periods in accordance with image data so that exposure is 
conducted on a silver halide photosensitive material, the apparatus 
comprises control means for obtaining light amount data for each recording 
element on the condition that plural pieces of the same kind of recording 
elements of the recording element to be obtained the light amount data are 
being driven, for obtaining a correction value for an exposure amount of 
each recording element on the basis of the light amount data, and for 
correcting the recording elements on the basis of the correction value. 
With the above method and the structure, as shown in FIGS. 13(a) and 13(b), 
in the case of the same kind of recording element of the recording element 
which is used in the image formation, that is, in cases where the light 
emission characteristic pattern of each element are similar to each other, 
the correction amount can be obtained with the use of the same kind of 
recording element of the recording element which is used for the image 
formation. In the invention, the exposure of the silver halide 
photosensitive material is conducted on the condition that the plurality 
of recording elements are driven, and light amount data are obtained by 
measuring the density of the exposed photosensitive material. 
With the above, since the correction value is calculated from the density 
measurement value, the density measurement values can be handled as light 
amount data on a condition equal to the condition that the recording 
elements are driven so as to actually output an image, and the correction 
value can be obtained in the end output form of the density including the 
influence of the multi-exposure effect by the plural time exposure and an 
intermittent exposure effect. Whereby a further better quality image 
without density unevenness can be obtained. 
In the invention, the relationship between the density data and the light 
amount data is obtained so that the density data are converted into light 
amount data and the correction value of the exposure amount of each 
recording element is obtained. 
With the above, the relationship between the density measurement value and 
the light amount in the total light emission time of the plural time 
exposures in which the exposure is conducted plural times is obtained and 
the density measurement value is converted into the light amount so that 
the correction value is obtained. By this measure, the discontinuity 
taking place during the plural time exposures in relationship between the 
emission time and the density can be corrected more precisely, the density 
unevenness caused by the influence of the discontinuity can be eliminated 
more precisely, and a far better image with less density unevenness can be 
obtained. Incidentally, herein, the discontinuity in the gradation means 
an irregularity which is caused by the responding characteristic of the 
light source and the photosensitive material during the plural time 
exposure. In particular, when the control with which the exposure is 
conducted on the basis of the correction value, the density is measured, 
and a correction value is obtained again is repeated, the consideration of 
the relationship between the light amount and the density is preferable, 
because the convergence ability is further enhanced. 
In the invention, the plural pieces of the recording elements are driven 
simultaneously so as to emit light and the exposure amount is measured, 
whereby the light amount data are obtained. 
With the above, since the light amount data are obtained directly, the 
control can be simplified. In addition, the measurement value measured on 
the condition becomes the data of the unevenness conspicuous portion on a 
similar condition of the light emitting condition in the actual image 
recording, the unevenness can be reduced so that a high quality image can 
be obtained. 
In the invention, the correction value for the exposure amount of each 
recording element is obtained with the use of the light amount data and a 
single light amount which is obtained by measuring an exposure amount in 
the case that the recording elements are driven one by one so that only a 
single element emits a light. 
With the above, by using the measurement value of a single element 
together, the small pitch density unevenness for each pixel can be reduced 
in addition to the unevenness of a large pitch, so that the high image 
quality can be obtained. 
In the invention, the light amount data is obtained by measuring an 
exposure amount of each recording element on the condition that a 
plurality of recording elements are emitting light simultaneously. 
With the above, since light measurement for a single element is conducted 
directly on the condition that plural recording elements are emitting 
light, a correction value can be calculated far more precisely, so that a 
high quality image can be obtained. 
In the invention, an image is formed on the silver halide photosensitive 
material in such a manner that the image data is stored for each line of 
the recording elements in the latch means, the enable signal which is 
converted into a combination of the same or different time widths in 
accordance with image data is generated by stages for every time the image 
data is latched by the latch means, each of the recording elements is 
driven respectively by the driving means on the basis of the enable signal 
generated by stages so as to conduct On-Off recording plural times in 
accordance with the time width of the enable signal. 
With the above, the driving means conducts the On-Off recording plural 
times for the silver halide photosensitive material in accordance with the 
time period of the enable signal. Accordingly, a continuous gradation 
recording can be conducted so that a high quality image is obtained 
without causing the apparatus to be complicated or at high cost. In the 
invention, the driving means conducts the On-Off recording plural times in 
accordance with the time width of the enable signal so that the length of 
the total recording time period of each recording element set by the 
enable signal generated by stages by the enable signal generating means 
corresponds to the magnitude of the gradation of the image data. Then, the 
image is formed by a recording head composed of the recording elements 
which are used to control a plurality of color lights corresponding to the 
plurality of photosensitive layers differing in color-sensitivity of the 
silver halide color photosensitive material. 
With the above, since the enable signal for each recording element can be 
set to conform with the sensitivity and gradation characteristics of each 
photosensitive layer of the silver halide color photosensitive material, a 
continuous gradation image with a high resolution can be recorded on the 
silver halide color photosensitive material with the utilization of the 
characteristics of the silver halide photosensitive material without 
causing the apparatus to be complicated or at a high cost. 
Further, with the effect of the intermittent exposure effect which is a 
characteristic of the silver halide color photosensitive material, the 
difference between the high and low sensitivities becomes large and the 
color cross talk can be reduced so that the color separation can be 
improved. In addition, the spread of dots can be further extended so that 
the density of each dot region is unified. As a result, a continuous 
gradation recording can be conducted so that a high quality image can be 
obtained without causing the apparatus to be complicated and a high cost 
for the purpose of the positional registration for each color. 
Furthermore, degradation in the image quality such as Moire patterns 
caused by the positional deviation of each color hardly take place, a 
complicated and expensive apparatus necessary for the position 
registration of each color are not needed in the above structure. 
In the invention, the recording head is composed of an LED array, a vacuum 
fluorescent tube array or a liquid crystal shutter array. With the above, 
since the plurality of recording elements arranged in an array form of a 
single line or plural lines are composed of the LED array, the vacuum 
fluorescent tube array or the liquid shutter array, the discontinuity of 
the gradation can be reduced. 
In the invention, the recording elements conduct an exposure for color 
photographic printing paper of a silver chloride photosensitive material 
so that an image is formed. Herein, the silver chloride photosensitive 
material is defined as a photosensitive material comprising a silver 
halide emulsion layer containing not less than 90 mol % silver chloride. 
The silver chloride photosensitive material tends to cause the density 
unevenness greatly due to the influence of the multi-exposure effect by 
the plural time exposures or the intermittent exposure effect. 
However, with the above, since the density unevenness is improved 
appreciably, the effect of the present invention for the silver chloride 
photosensitivity material is greater and the developing process can be 
conducted at a high speed. 
In the invention, in the time that each time width of the enable signal 
generated by stages is converted into a multi-valued digital value in 
accordance with the gradation of the image data, the driving means changes 
each time width sequentially in accordance with the weight in each bit in 
the time that the digital value is represented in binary numbers and 
drives each recording element individually so as to conduct On-Off 
recording. 
With the above, the enable signal corresponding to the density value of the 
image data can be set without causing the apparatus to be complicated and 
a high cost. In the invention, the driving means drives each recording 
element individually so as to conduct On-Off record with each time width 
of 2.sup.n T+t of the enable signal, wherein "n" is either 0, 1, 2, . . . 
which is a bit number in the time that each time width of the enable 
signal is converted in a digital value in accordance with the gradation of 
image data, "T" is a unit of time, "t" is a negative or positive value of 
a predetermined time. 
With the above, since the time period of the enable signal can be adjusted 
respectively by increasing or decreasing "t", a smoother gradation 
recording can be conducted. 
In the invention, each time width of the enable signal generated by stages 
is made constant, the driving means drives each recording element 
individually so as to conduct On-Off recording by the number of times of 
the value of the image data. 
With the above method, the apparatus can be a simpler structure and similar 
gradation recording can be realized by a simpler structure. 
In the invention, the enable signal generating means changeably sets the 
predetermined time width of the enable signal generated by stages. 
With the above, since the time period of the enable signal can be finely 
adjusted, the gradation characteristics can be adjusted in accordance with 
the output characteristics of the apparatus. 
In the invention, the plurality of recording elements are aligned in the 
array form of a single line or plural lines, the ratio of the exposure 
size of a single recording element in the aligned direction to the 
recording pitch in the aligned direction is 0.7 to 1.2. Herein, the 
exposure size does not means the size the formed image after the 
recording, and means the size of exposing optical image of a single 
recording element on the surface of the recording medium. 
With the above, more continuous gradation characteristics can be obtained. 
In the invention, the plurality of recording elements are aligned in the 
array form of a single line or plural lines, the ratio of the exposure 
size of a single recording element in the vertical direction with regard 
to the aligned direction to the recording pitch in the vertical direction 
with regard to the aligned direction is 0.3 to 1.0. With the above, more 
continuous gradation characteristics can be obtained. 
In the invention, in the case that the plurality of recording elements are 
aligned in the array form of a single line or plural lines, the exposure 
size of a single recording element in the vertical direction with regard 
to the aligned direction is defined as "A", the recording pitch in the 
vertical direction with regard to the aligned direction is defined as "B", 
and the ratio of the time period from the start of light emission to the 
completion of light emission for a single line to the recording time cycle 
for the single line is defined as "C", the recording is conducted so as to 
satisfy the following formula: 
EQU 0.8.ltoreq.(A/B+C).ltoreq.1.3 
With the above, more continuous gradation characteristics can be obtained. 
In the invention, in the time of the gradation recording conducted by 
stages, an interval time period between each enable signal in which the 
enable signal is in a rest condition is set more than 2 micro-seconds and 
then the recording is conducted. With above, since the influence of the 
light emission history may be reduced by the just-before enable signal, it 
becomes possible to control the gradation characteristics with the time 
width of the enable signal. Especially, in cases where the exposure is 
conducted while moving, the spread of dot is widened so that unevenness 
caused in the time of area modulation can be reduced. 
In the invention, shift control means is provided for conducting shift 
control in such a manner that shifting and stopping of the silver halide 
color photosensitive material is repeated in the vertical direction with 
regard to the aligned direction of the recording elements, and the 
recording is conducted with the use of the exposure more than 50% of the 
time period from the start of light emission to the completion of light 
emission of the recording elements for a single line while the silver 
halide color photosensitive material is shifting on the basis of the shift 
control by the shift control means. 
With the above, since the exposure is conducted while conducting the 
shifting, the density in the dot region can be unified and the responding 
ability in the gradation control can be improved. 
In the present invention, further, by the structure equipped with a 
plurality of recording elements which are arranged in an array form of a 
singe line or plural lines and are controlled independently, means for 
correcting deviation in amount of light emission of each recording element 
on the basis of correction data, and exposure control means for conducting 
exposure in 512 levels or more on a silver halide light sensitive material 
by controlling the recording elements to conduct On-Off driving plural 
times with a combination of the same time width or different time widths 
in accordance with image data; it become possible to provide an apparatus 
with the following effects. A high quality image having no irregularities 
on an even image, in particular, such as a skin of a person or a sky in a 
background can be obtained without losing the highest density. The 
apparatus dose not become complicate or high cost. Further, the apparatus 
forms a continuous gradation image with high quality by utilizing a 
characteristics of the silver halide light sensitive material. 
Incidentally, image data in the present invention means that data value 
corresponds to an image. For example, when original data of an image has 
gradations less than 512 levels, by converting the image data so as to 
become 512 levels or more, by correcting the image data and by conducting 
image formation with the image data, it becomes possible to obtain the 
remarkable effects of the present invention. When original data of an 
image is 512 or more, it may be possible to handle the original data as 
the image data without any change or to use the original data after 
conversion. 
Further, by the structure that the gradation attained by a plurality of 
On-Off driving of the recording element is made 65536 levels or less, it 
become possible to provide an apparatus with the following effects. The 
apparatus can be more simplified at low cost without failing to form high 
quality image having no density irregularity. Further, the processing 
speed can be enhanced. 
Furthermore, in the present invention, by the structure that the correction 
data to correct the recording element is calculated from an amount of 
light emissions which is obtained for each recording element on a 
condition that plural recording elements among recording elements or the 
same kinds of recording elements arranged in an array form are driven, 
since the correction is conducted on the basis of the result obtained from 
an amount of light emission of each recording element on a condition 
similar to an actual image recording in which plural recording elements 
are driven, deviation in light emitting characteristics is more precisely 
corrected in comparison with the case that the correction is conducted on 
the basis of an amount of light obtained by driving the recording elements 
one by one under the condition apart from the actual recording. As a 
result, a high quality image with less irregularity in density can be 
formed. 
By the structure that the silver halide light sensitive material used in 
the present invention comprises a plurality of light sensitive layers 
differing in sensitive color and each recording element arranged in an 
array form is controlled independently so as to conduct exposure with a 
color light among a plurality of color light corresponding to the 
plurality of light sensitive layers and at least the gradation of an 
exposure of green color can be controlled in 512 levels or more, at least 
the green exposure can be controlled in the case that the silver halide 
light sensitive material is a color light sensitive so that the apparatus 
can be simplified at low cost, a processing is conducted at a high speed, 
density irregularities on a color image can be reduced, and a more high 
quality color image can be formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, the embodiment of the present invention will be explained with 
reference to the drawings. The embodiment is only one example of the 
present invention, and the present invention is not limited to this 
embodiment. FIG. 1 is an outline view showing a structure of an image 
recording method. A color photographic printing paper 2 (hereinafter 
simply referred to printing paper) of a silver halide color photosensitive 
material is drawn out from a roll by a supporting drum 1 acting as a shift 
control means which is driven and rotated by an unillustrated conveyance 
driving source. When the printing paper 2 is conveyed in the arrowed 
direction, a red color light source printing head 30a, a green color light 
source printing head 30b and a blue color light source printing head 30c 
are subjected to an exposure control in accordance with image data by a 
printing head control section 40 so that required positions of the 
printing paper 2 are sequentially exposed for each color and a latent 
image of a color image is formed on the printing paper 2. After the 
exposure process has been completed in the above manner, the printing 
paper 2 is conveyed to a developing process by the supporting drum 1 in 
order to be subjected to the next process. 
Incidentally, an array light source in which recording elements are 
arranged in a single line or plural lines is used for each printing head. 
For more detail, a LED light source which is generally used is adopted for 
the red color light source printing head 30, and a vacuum fluorescent 
printing head or Vacuum Fluorescent Print Head (hereinafter simply 
referred to VFPH) which is easily subjected to color separation by a color 
filter with a relatively high luminance and a high speed response is 
adopted for the green color light source printing head 30b and the blue 
color light source printing head 30c. As for the printing paper 2, it was 
explained as being in the form of a roll. However, the printing paper 2 
may also be in the other form. Further, as for the shift means for the 
printing paper 2, the other conveying techniques may also be used. 
A light receiving sensor 55 is disposed beneath the printing head through 
the supporting drum 1. Before the recording operation is conducted, the 
light receiving sensor 55 receives light from each of the printing heads 
30a, 30b, 30c, converts the intensity of the light into an electronic 
signal with its internal photo-electric converting element, and then 
outputs the signal to the correction process section 60. Upon receipt of 
the signal, the correction process section 60 outputs correction data to 
correct the light emission characteristics of each of the printing heads 
30a, 30b, 30c to the printing head control section 40. Based on the 
correction data, the printing head control section 40 regulates the light 
emission characteristic of each of the printing heads 30a, 30b , 30c. 
FIG. 2 is a diagram explaining a writing operation of the printing head in 
which image data for one color component are written. 
In FIG. 2, when the printing head control section 40 receives image data 
showing the gradation of each color component with a digital value of 8 
bits or 12 bits, the printing head control section 40 conducts the 
correction process for the image data on the basis of the above correction 
data, converts the image data into serial digital image data corresponding 
in amount to one line of pixels for each recording element, generates a 
set pulse signal to transport bit data of the image data to a latch 
circuit 32 and an enable signal to control the light emitting time, and 
outputs to the printing head 30 for one color. The bit data of the image 
data means data as to a specific bit of the image data. 
Initially, when data of MSB (Most Significant Bit) as the bit data of the 
image data corresponding in amount to one line is transmitted from the 
printing head control section 40 to a shift register 31 in the printing 
head 30, a set pulse signal is inputted in the latch circuit 32, and the 
data of MSB corresponding in amount to one line are latched together in 
synchronization with the set pulse signal. 
Then, the enable signal corresponding to the gradation is inputted into a 
driver circuit 33, during a time period defined by the enable signal, each 
recording element in the recording elements which are arranged in an array 
form of one line or plural lines is controlled and driven so as to emit 
light in accordance with the latched image data. In other words, the 
driver circuit 33 selectively sends an enable signal to the recording 
elements in the recording array 34 whose latched data is "1", and causes 
the elements to emit light during the time period defined by the enable 
signal. The emitted light is focused on the printing paper 2 through a 
Selfoc lens array 35 and forms a latent image. In this manner, the 
operation is conducted sequentially for all of the 8 bits from MSB to LSB 
(Least Significant Bit), thereby the recording for one line is completed. 
Incidentally, the operation for one color was explained above, the 
operation for three colors is conducted in the same way of the above 
operation. Incidentally, the operation order for bits may be conducted 
from LSB to MSB or in the other order. The operation order is not limited 
to the above example. 
VFPH which has the light emission characteristic for green component and 
blue component is provided with an unillustrated color separation filter 
for each of green and blue beneath the Selfoc lens array 35. Since the 
printing head control section 40 conducts the recording control in such a 
manner that exposure timing of each of the three sets of printing heads is 
delayed one after another so as to record image data transmitted for each 
color on the required position on the conveyed printing paper 2, the color 
image can be recorded properly. A yellow filter may be used as the filter 
for a green light source instead of a green filter. The printing head 
control section 40 conducts the recording control for the printing head 30 
so that 50% or more of the recording amount of one line is conducted while 
the printing paper 2 is shifting by the supporting drum 1, whereby the 
recorded image is continued between lines. As a result, the occurrence of 
uneven images can be avoided and smooth continuous gradation can be 
attained by the density modulation. 
Incidentally, the LED array and VFPH are adopted in the present embodiment. 
However, instead of them, a combination of light emitting member and a 
shutter array (liquid crystal shutter array, PLZT shutter array, etc.), a 
laser array (LD laser array, etc.) in which lasers are aligned, may also 
be used in a proper combination. Further, as photosensitive material used 
for the exposure process, the photographic color printing paper 2 
including silver chloride was used. However, if the silver halide 
photosensitive material is a so called low contrast recording medium with 
which an image density can be controlled by the area modulation, such the 
low contrast recording medium may be used in the present embodiment. Also, 
if an array suits the color sensitivity of the photosensitive material, 
the array may be used in the present embodiment. In the case of the color 
recording, a three color control in which light sources for three colors 
are arranged on a single printing head may also be conducted. 
An LED array made of a material such as GaAlAs or GaAsP is a high light 
emission efficiency element in comparison with the other LED array. 
Specifically, an LED array which has a sharp peak in the 650 nm to 680 nm 
range of the emitting wavelength can selectively expose the red light 
sensitive layer of the silver halide photosensitive material with high 
efficiency. Further, since it may be possible to conduct On-Off control at 
high speed on the order of several nano seconds, the LED array especially 
suits severe exposure time control. 
In VFPH using oxidized zinc phosphor (ZnO:Zn), since light emission is 
caused in a wide spectral region extending from blue light to green light, 
a blue sensitive layer and a green sensitive layer of the silver halide 
color photosensitive material can be selectively exposed with the 
combination of VFPH and a color filter. Further, since the light emission 
efficiency is relatively high and temperature change during light emission 
is small, the shift of the peak wavelength of the emitting light caused by 
the temperature change is small and the exposure efficiency for the silver 
halide photosensitive material which has a high wavelength selecting 
tendency becomes stable. 
In cases where a combination of a liquid crystal shutter and a light 
emitting member are used as the recording elements 34, since a possibility 
to make the array in a two dimensional form is high, the combination is 
particularly suitable for the purposes of conducting recording at a higher 
speed and recording the image in a larger size. Further, in cases where 
making two dimensional forms, it is possible to not make the total 
outputting speed of the image slow even if the exposure time for each 
element is made relatively long, and a discontinuing tendency in the 
gradation caused by plural times of exposure is small so that a good 
gradation can be obtained. Still further, since LED arrays, VFPH, a 
ferroelectricity liquid crystal shutter has a high speed switching 
capability, a discontinuing tendency in the gradation caused by plural 
times of exposure is also small so that good gradation is obtained. 
When the present embodiment is applied to a photosensitive material having 
a soft gradation characteristic, such as a silver halide photosensitive 
material, the highest efficiency can be obtained, and a real density 
modulated image can be obtained by the density control in a small region 
by the effect of the light emitting time control so that a smooth 
pictorial image quality can be obtained. FIG. 3 shows a detailed block 
diagram of the printing head control section 40. Its operation will be 
explained as follows. 
Firstly, a multiplier 41 multiplies the image data by the correction data 
in order to conduct the correction of the light emitting characteristic 
obtained in the correction process section 60 as mentioned above, then the 
corrected image data is outputted to an interface 42. CPU 43 sets an 
initial count value to count pixels corresponding to one line in counter 
44 through the interface 42 so that the counter 44 is started, and 
controls the demultiplexer 45 for changing the input. Upon receipt of this 
operation, counter 44 starts counting and outputs the count value to 
demultiplexer 45. Then, on the basis of the above count value, the image 
data (8 bits or 12 bits.times.one line) are written in a line memory 46. 
When the writing operation to write the image data of the first line in the 
line memory has been completed, the bit data of the image data of the 
first line are outputted sequentially from MSB to LSB from the line memory 
46 to the multiplexer 48, and then transmitted to the printing head 30. On 
the other hand, the output passage for the image data of the second line 
is changed by the demultiplexer 45 so that the image data of the second 
line are written in the line memory 47. In such a manner, during the time 
period that the bit data of the image data of the current line is 
transmitted to the printing head 30, the image data of the next line is 
subjected to the writing operation so as to be written into a line memory 
other than the line memory in which the image data of the current memory 
is written. Since such an expansion process and writing operation are 
repeated, the image data of each line are continuously outputted without 
delays in time. 
Counter 49 counts the time to transmit the bit data of the image data to 
the multiplexer 48 under the control of the CPU 43 and outputs a count-up 
signal to a set pulse signal generating circuit 50. When the transmitting 
operation to transmit the bit data of the image data to the printing head 
30 has been completed, the set pulse signal generating circuit 50 
generates a set pulse signal and outputs it to the printing head 30, and 
also outputs the set pulse signal to the enable signal generating circuit 
52. 
On the other hand, the counter 51 counts an enable time corresponding to 
the density value assigned in advance for each bit of 8 bits or 12 bits 
under the control of the CPU 43 and outputs the enable signal generating 
circuit 52. Then, the enable signal generating circuit 52 generates an 
enable signal having an enable time corresponding to MSB of 8 bits or 12 
bits representing the density value upon receipt of the generation of the 
set pulse signal and outputs it to the printing head 30 and to the CPU 43. 
Upon receipt of it, the CPU 43 controls the counter 49 so as to generate 
the next set pulse signal. By repeating such successive operations, the 
set pulse signal, the enable signal and the bit data of the image data are 
sequentially outputted from MSB to LSB for each line with a timing 
relating to each other to the printing head 30. 
FIG. 4 shows a detailed block diagram of the correction data processing 
section. 
A light receiving sensor driving system 62 conducts a light receiving 
control for a light receiving sensor 55 under the control of a light 
receiving sensor control section 61. That is, before the recording on the 
printing paper 2 is started, the light receiving sensor 55 is shifted to 
the image forming position of each of the three printing heads provided 
for each color, and conducts the light receiving operation. At this time, 
the supporting drum 1 is provided with a slit of a small gap through which 
the light receiving sensor 55 conducts the reading. The light receiving 
sensor 55 receives the emitting light sequentially for each color through 
the slit. 
Analog electronic signals outputted from the light receiving sensor 55 are 
amplified by the amplifying circuit 64. Then, the signals are converted 
into digital electric signals with an A/D converter and the digital 
electronic signals are stored in a memory 67. Next, an arithmetic process 
is applied as required so that the correction data are calculated and are 
inputted and stored in a look-up table in the correction memory 66. 
Alternatively, the correction data may be inputted from the outside the 
unit and stored in the look-up table in the correction memory 66. With the 
look-up table, the correction data corresponding to the intensity of the 
receiving light is outputted. 
FIG. 5 shows a timing chart of the output signal outputted from the 
printing head control section 40 to the printing head 30b. Among the image 
data which has been subjected to an expansion process so as to form a 
density value structured in 8 bits for each pixel, firstly, MSB 
corresponding to one line are outputted over 300 sec and are transmitted 
to the printing head 30b, thereafter the set pulse signals and the enable 
signals are outputted. A time interval between the enable signals is set 
at 300 sec. 
At this time, the time period of the enable signal of each color is as 
follows: 
______________________________________ 
B G R 
______________________________________ 
MSB 1536 .mu.s 2560 .mu.s 
5120 .mu.s 
2nd bit 768 .mu.s 1280 .mu.s 
2560 .mu.s 
3rd bit 384 .mu.s 640 .mu.s 
1280 .mu.s 
4th bit 192 .mu.s 320 .mu.s 
640 .mu.s 
5th bit 96 .mu.s 160 .mu.s 
320 .mu.s 
6th bit 48 .mu.s 80 .mu.s 
160 .mu.s 
7th bit 24 .mu.s 40 .mu.s 
80 .mu.s 
LSB 12 .mu.s 20 .mu.s 
40 .mu.s 
______________________________________ 
In this case, when the latch data or the bit values for all of the enable 
signals from MSB to LSB for an element are "1", the emitting light shows 
the highest density. The same control is conducted for the printing heads 
30a and 30c. 
FIG. 14 is a timing chart of output signals in the case that image data of 
each pixel is extended into density value composed of 12 bits and an 
interval time between enable signals is set to 48 .mu.sec. 
At this time, time periods of enable signals for each color are as shown in 
table 1. 
TABLE 1 
______________________________________ 
Red 30a Green 30b 
Blue 30c 
Bit (.mu.sec) (.mu.sec) 
(.mu.sec) 
______________________________________ 
MSB 204.8 614.4 614.4 
2nd bit 102.4 307.2 307.2 
3rd bit 51.2 153.6 153.6 
4th bit 25.6 76.8 76.8 
5th bit 12.8 38.4 38.4 
6th bit 6.4 19.2 19.2 
7th bit 3.2 9.6 9.6 
8th bit 1.6 4.8 4.8 
9th bit 0.8 2.4 2.4 
10th bit 0.4 1.2 1.2 
11th bit 0.2 0.6 0.6 
LSB 0.1 0.3 0.3 
______________________________________ 
In the above manner, since the enable signal for each bit of blue, green 
and red can be set to conform with the sensitivity and the gradation 
characteristics of each sensitive layer of the silver halide color 
photosensitive material, each recording element may be driven individually 
a plural number of times in the manner of On-Off recording, whereby a 
continuous gradation image with a high resolution can be recorded on a 
silver halide color photosensitive material with the utilization of the 
characteristic of the silver halide color photosensitive material without 
causing the apparatus to be complicated and at high cost. 
The difference between the high sensitivity and the low sensitivity 
increases due to the intermittent exposure effect of the silver halide 
photosensitive material, resulting in that a color cross talk in exposure 
time can be decreased and the color separation can be enhanced. For 
example, speaking of the high density region of the color printing paper, 
since blue is slightly exposed by the green exposure, yellow is mixed in 
magenta after development, thereby causing the color cross talk with 
yellow. However, in the present invention, since On-Off exposure is 
conducted plural times, the color cross talk with yellow by the blue 
sensitive layer can be reduced, thereby obtaining a higher image quality. 
Further, with the high contrast recording medium by the electrophotgraphy 
or a so-called silver developing technique such as a monochrome 
photosensitive material in a silver halide photosensitive material with 
which a silver image is formed, since the spreading of a pixel is small, 
the image is formed with the area modulation tendency, resulting in that 
an irregularity in a unit of a pixel is observed in the image and the 
obtained image is unacceptable. Further, since a pixel does not spread and 
its shape is distinct, the positional deviation among yellow, magenta and 
cyan pixels causes Moire patterns. Whereby, the image quality tends to be 
degraded. As a consequence, it is necessary to precisely register the 
position of the pixels for each color. 
In contrast, in the present invention, with the so-called color developing 
method of forming a dye image by the development such as a silver halide 
color photosensitive material, the spread of a pixel is widened by plural 
On-Off exposure, the density in each pixel region tends to be unified, and 
the irregularity in unit of a pixel decreases, thereby obtaining a higher 
quality image. Further, since it is not necessary to use a complicated 
apparatus to conduct a high precision positioning, the cost does not 
increase. In this way, with the present embodiment, a continuous gradation 
recording with a higher resolution may be conducted with the utilization 
of the exposure characteristics of the printing paper 2 without causing a 
complicated apparatus and a high cost. 
An example in which the image output was conducted with the present 
apparatus will be indicated hereinafter. 
Inventive Example 1 
The correction was conducted in the following procedure in the LED array 
which was the red light source printing head 30a and an image for the 
evaluation was outputted. Incidentally, the following two types of images 
were used as the image for the evaluation. 
Image A: uniform density solid images classified into 5 stages of low 
density to middle density. 
Image B: an image including a relatively large figure of a person on a 
background of gray gradation. 
1) All recording elements were controlled to emit light on the basis of the 
image data with which the density value on the printing paper 2 was 
expected to be approximately 1.0, the printing paper 2 was exposed with 
the lights and developed so that images for the correction process were 
obtained. 
2) The image density data were obtained in such a manner that the density 
measurement was conducted in a printing head 30a-aligned direction on the 
image for the correction process obtained by the above operation by a 
density measuring device (Konica Microdensitometer PDM-5 Type BR: 
manufactured by Konica Corporation). 
3) FIG. 11 shows an example of the density data obtained in the above 
manner. 
The density data became a form in which a peak was indicated for the 
position of each recording element. On the basis of this form, the density 
peak position (i) for each of all recording elements was detected. 
4) Several data (5 data in this example) located before and after the peak 
point (i) obtained the above were summed up together with the peak density 
data so that the summed-up density data (Di) were calculated. The same 
calculation was conducted for all recording elements. 
5) A correction value (Ci) was calculated from the density ratio of a 
reference summed-up density (Do: the average value of all summed-up 
density data) to the obtained summed-up density data (Di), and the 
correction value was stored in the correction memory 66. 
EQU Ci=Do/Di 
6) The image data to be evaluated were multiplied with the correction data 
by the multiplier 41, and the printing paper 2 was exposed with the 
corrected image data. 
7) The exposed printing paper was subjected to a predetermined developing 
process, whereby the image data to be evaluated was obtained. 
Inventive Example 2 
The correction was conducted with the following procedure in the LED array 
which was the red light source printing head 30a and an image for the 
evaluation was outputted. Incidentally, the image for the evaluation was 
the same as that in Inventive Example 1. 
1) All recording elements were controlled to emit light on the basis of a 
plurality of the image data differing in density value, the printing paper 
2 was exposed with the light and developed so that images for the 
correction process were obtained. 
2) The density measurement was conducted in the same manner of Inventive 
Example 1 for the image for the correction process obtained by the above 
operation. As a result, a plurality of summed-up density differing in the 
image data value were obtained for each recording element. 
3) A relationship between the image data value (proportional to the light 
amount of the recording element) and the density value was obtained for 
all recording elements. The image data value in the time of the specific 
target density (for example: density 1.0) was calculated as the light 
amount (Pi) from the above relationship. 
4) A correction value (Ci) was calculated from the light amount ratio of a 
reference light amount (Po: the average value of all light amount) to the 
obtained light amount (Pi). 
EQU Ci=Po/Pi 
5) The correction was conducted in the same manner as Inventive Example 1 
on the basis of the obtained correction value (Ci), whereby the image data 
to be evaluated was obtained. 
Comparative Example 1 
The correction was conducted in the following procedure in the LED array 
which was the red light source printing head 30a and an image for the 
evaluation was outputted. Incidentally, the image for the evaluation was 
the same as that in Inventive Example 1. 
1) On the condition that one recording element (i-th element) was emitting 
a light, the luminance (Ei) was measured by the light receiving sensor 55. 
2) The above measurement was conducted sequentially for each element by the 
control of the light receiving sensor driving system 61 on the basis of 
the light receiving sensor control section 61. 
3) A correction value (Ci) was calculated from the luminance ratio of the 
reference luminance (Eo) to the obtained luminance (Ei) in the correction 
data calculating section 68, and the correction value was stored in the 
correction memory 66. 
EQU Ci=Eo/Ei 
4) The image data to be evaluated were multiplied with the correction data 
by the multiplier 41, and the printing paper 2 was exposed with the 
corrected image data. 
5) The exposed printing paper was subjected to the predetermined developing 
process, whereby the image data to be evaluated was obtained. 
Comparative Example 2 
The correction was conducted in the following procedure in the LED array 
which was the red light source printing head 30a and an image for the 
evaluation was outputted. Incidentally, the image for the evaluation was 
the same as that for Inventive Example 1. 
1) In the case that one recording element (i-th element) was controlled to 
emit a light with the specific image data value, the light was emitted 
plural times in accordance with the image data value as shown in the 
timing chart in the FIG. 5. 
Under such conditions, the summed-up light amount (Ii) of all emitted 
lights was measured by the light receiving sensor 55. 
2) The above measurement was conducted sequentially for each element by the 
control of the light receiving sensor driving system 61 on the basis of 
the light receiving sensor control section 61. 
3) A correction value (Ci) was calculated from the luminance ratio of a 
reference light amount (Io) to the obtained light amount (Ei) in the 
correction data calculating section 68, and the correction value was 
stored in the correction memory 66. 
EQU Ci=Io/Ii 
(the average light amount of all measured elements was used as Io) 
4) The correction was conducted in the same manner of Comparative Example 1 
on the basis of the obtained correction value (Ci), whereby the image data 
to be evaluated was outputted. 
For the obtained image, the visual evaluation was conducted in terms of the 
density unevenness for Image A and in terms of both the density unevenness 
and the gradation for Image B. 
As a result, with regard to Image A to be evaluated, Inventive Example 1 
showed less unevenness and a uniform image in terms of density in 
comparison with Comparative Example 1 and Comparative Example 2. Further, 
with regard to Image B, Inventive Example 1 showed a higher quality image 
which had less unevenness and better continuous gradation in gradation of 
the background and in the person's skin in comparison with Comparative 
Example 1 and Comparative Example 2. 
With regard to Image A to be evaluated, Inventive Example 2 showed much 
less unevenness and a much more uniform image with an improvement in 
accuracy of the correction in comparison with Inventive Example 1. 
Further, with regard to Image B, Inventive Example 2 showed a higher 
quality image with much less unevenness and better continuous gradation in 
comparison with Inventive Example 1. 
Inventive Example 3 
In the case of formed image 1 in which a solid image was formed which has a 
uniform density in a predetermined area, and has a stepped-density, in 
which a time period from the minimum exposure time to the maximum exposure 
time was divided into several steps of time, and in a case of a formed 
image 2 in which an image, including a close-up of a face of the subject 
with a gray gradation background, was formed, the maximum number of times 
of light emission in the plural number of times of exposure, that is, the 
number of gradations is shown by the number of bits in Table 2, and the 
time period of the enable signal was appropriately adjusted and unified. 
By using an output condition 1 in which the density of an image formed in 
the maximum exposure time was approximately equal to the maximum density 
of a photosensitive material itself in the evaluation by visual 
observation, and an output condition 2 in which the density unevenness is 
scarcely remarkable in a solid image having an intermediate density, 
processing from image formation through development was carried out. 
Concerning the obtained image, the maximum density was evaluated from a 
portion on the formed image 1 corresponding to the step of a high exposure 
time period or from a portion of a subject's hair. Further, the density 
unevenness was evaluated from an intermediate density portion of the 
formed image 1 or from a portion of a subject's skin of the formed image 
2. 
TABLE 2 
______________________________________ 
Example Max. number of 
Number of 
Output 
No. light emission 
gradation 
condition 
______________________________________ 
1 9 512 1 
2 9 512 2 
3 12 4096 1 
4 12 4096 2 
5 16 65536 1 
6 16 65536 2 
7 17 131072 1 
8 17 131072 2 
______________________________________ 
When the number of gradations is more than 512, an image forming apparatus 
which can form a high quality image having excellent gradation continuity 
can be provided, little density unevenness, and acceptable maximum 
density, without increasing the complexity of the apparatus nor increasing 
the cost. 
Further, when the number of gradations is less than 65536, each pixel can 
handled with a unit of 2 byte, on the other hand, when the number of 
gradations is more than 65536, it is necessary to handle each pixel with a 
unit of 3 byte. According, in the case that the number of gradations is 
less than 65536, the time period required for processing and the required 
memory capacity are reduced to almost 2/3, compared to the cases that the 
number of gradations is more than 65536, and the necessary circuit can be 
simplified, resulting in an acceptable apparatus. 
Inventive Example 4 
The light source of the binary recording element of the above described 
example, was replaced with a light source of a multi-valued recording 
element, and an image evaluation relating to a change of the number of 
gradations was carried out in the same manner as in Inventive Example 3. 
In this connection, the multi-valued recording element in Inventive 
Example 4 represents the following. For example, in the case of a 
16-valued recording element, which represents a light source in which each 
recording element is controlled by the gradation control and the light 
emission time control at 16 levels (which correspond to levels expressed 
by 4 bits on the binary recording element). When the enable signals for 2 
time exposures are set by using this light source, control of 256 
gradations, at the maximum, can be carried out. 
TABLE 3 
______________________________________ 
Example Recording 
Max. number of 
Number of 
Output 
No. element light emission 
gradation 
condition 
______________________________________ 
1 4 valued 5 1024 1 
2 4 valued 5 1024 2 
3 4 valued 8 65536 1 
4 4 valued 8 65536 2 
5 4 valued 9 262144 1 
6 4 valued 9 262144 2 
7 16 valued 
3 4096 1 
8 16 valued 
3 4096 2 
9 16 valued 
4 65536 1 
10 16 valued 
4 65536 2 
11 16 valued 
5 1048576 1 
12 16 valued 
5 1048576 2 
______________________________________ 
When the number of gradations is more than 512, an image forming aparatus 
can be provided, which can form a high quality image having an excellent 
gradation continuity, little density unevenness, and an acceptable maximum 
density, without increasing the complexity of the apparatus nor increasing 
the cost. 
Further, when the number of gradations is less than 65536, a time period 
required for processing and the necessary memory capacity are reduced to 
almost 2/3, compared to the case in which the number of gradations is more 
than 65536, and the necessary circuit can be simplified, resulting in an 
acceptable apparatus. 
Incidentally, the recording element in which light emission time can be 
controlled, was used as the multi-valued recording element in Inventive 
Example 4, however, when the multi-valued recording element in which light 
emission intensity can be controlled is used, an appropriate enable signal 
is set, so that the image can be formed. 
In Inventive Examples 3 and 4, even when exposure is carried out by using 
respective 3 color recording heads 3R, 3G and 3B independently, and an 
image is formed, almost the same effects can be obtained. In the case 
where each of the 3 color recording heads is used so that an natural image 
such as the formed image 2, is outputted, it is most effective that the 
green light source recording head 3G is controlled within the range of the 
present invention, so that an acceptable image is formed. 
Inventive Example 5 
After the correction by Correcting Method 5-1 same as in Inventive Examples 
1 and Correcting Method 5-2 same as in Inventive Example 2, images were 
formed and evaluation was conducted with the same method as that in 
Inventive Examples 3 and 4. As a result, high quality image having 
irregularities fewer than Inventive Examples 3 and 4 could be obtained. 
Further, by Correcting Method 5-2, an excellent image having density 
unevenness less than that by Correcting Method 5-1, in particular, having 
fine pitch and less unevenness could be obtained. In Inventive Examples 1, 
2 and 5, as the density measuring device, Konica Microdensitometer PDM-5 
Type BR, manufactured by Konica Corporation was used. Instead of it, 
various types of scanners such as a flat bed scanner and a commercial drum 
scanner were used to measure the density. The same evaluation technique of 
Inventive Examples 1 and 2 was conducted for the measured density. As a 
result, the same effects were obtained. 
In Inventive Examples 1 and 2, as the reference summed-up density (Do) and 
the reference summed-up light amount (Po), the average value of all 
recording elements was used. Instead of it, the maximum value or the 
minimum value among th values of all recording elements was used and the 
same evaluation was conducted. As a result, the same effects were 
obtained. 
In Inventive Examples 1 and 2, the image for the correction process and the 
image for the evaluation were formed on printing paper (papers including a 
silver halide photosensitive material). As the silver halide 
photosensitive material, a transparent or a semitransparent printing 
paper, a negative film, a reversal film, a reversal paper, a monochrome 
photosensitive material, and a photosensitive material having a 
self-processing solution such as an instant photosensitive material may be 
used and the same effects can be obtained. 
Further, a photosensitive material on which the image for the correction 
process is formed may be different from a photosensitive material on which 
an image is actually formed. With regard to a point that the correction 
including the characteristic of the photosensitive material can be 
conducted, it is preferable to use the same photosensitive material. 
Still further, when necessary, the correction is conducted with the use of 
the obtained correction value, then the image for the correction process 
is outputted. The obtaining operation to obtain the correction value in 
the same manner may be repeated. 
Inventive Example 6 
The correction was conducted in the following procedure in the LED array 
which was the red light source printing head 30a and the images A and B 
for the evaluation were outputted. 
1) On condition that the two neighboring recording elements (ith and i+1th 
elements) are emitting light respectively, the light receiving element 55 
measured the total luminance (E2i) of the two recording elements. A light 
receiving sensor large enough to measure the luminance of the two elements 
simultaneously was used. 
2) The above measurement was conducted for each element sequentially under 
the control of the light receiving sensor driving system 61 on the basis 
of the light receiving sensor control section 61. 
3) In the correction data calculating section 68, the following averaging 
process was conducted for the measurement value (E2i) and the luminance 
(Ei) was obtained for each element. 
EQU Ei=(E2i+E2i+1)/4 
4) A correction value (Ci) was calculated from the luminance ratio of a 
reference luminance data (Eo: the average value of all summed-up luminance 
data) to the obtained luminance data (Ei), and the correction value was 
stored in the correction memory 66. 
EQU Ci=Eo/Ei 
5) The image data to be evaluated were multiplied with the correction data 
by the multiplier 41, and the printing paper 2 was exposed with the 
corrected image data. 
6) The exposed printing paper was subjected to a predetermined developing 
process, whereby the image data to be evaluated was obtained. 
For the obtained image, the same evaluation of Inventive Example 1 was 
conducted. 
As a result, with regard to Image A for the evaluation, Inventive Example 6 
showed less unevenness in terms of large-pitch unevenness and a uniform 
image in each density in comparison with Comparative Example 1. 
Further, with regard to Image B, Inventive Example 6 showed a higher 
quality image with less unevenness in terms of large-pitch unevenness and 
better continuous gradation in gradation of the background and in the skin 
of the person in comparison with Comparative Example 1. 
In Inventive Example 6, while a single set of sensors was being moved along 
the array, the measurement for each element was conducted. However, if 
plural sets of sensors are used, the same effects can be obtained. 
Further, if a sensor array such as a linear CCD is used and the 
measurement is conducted without moving the sensor, the same effects can 
be obtained. 
Further, the luminance (Ei) of each element was obtained by the averaging 
process, the calculating process is not limited to this example. If the 
luminance (Ei) of each element is obtained by the calculating process such 
as a center value, the same effects can be obtained. 
Still further, the simultaneously emitting light of the two elements was 
indicated as one example. A number of the measurement is not limited to 
this example. If the plural elements emit light simultaneously, the same 
effects can be obtained by obtaining the luminance (Ei) for each element 
with an appropriate calculating process. 
Inventive Example 7 
The correction was conducted in the following procedure in the LED array 
which was the red light source printing head 30a and images A and B for 
the evaluation were outputted. 
1) In an element chip (128 pixel in this embodiment) constructing LED 
array, the luminance (E1(j), E2(j), E3(j), E4(j)) were measured by the 
light receiving sensor 55 under the conditions indicated below. 
(j: element No. in the chip) 
E1(j) luminance measured on condition that a single recording element was 
emitting light. 
E2(j) the total luminance of two neighboring recording elements (jth and 
j+1th elements) were measured on condition that the two neighboring 
recording elements were emitting light. 
E3(j) the total luminance of three neighboring recording elements (j-1th, 
jth and j+1th elements) were measured on condition that the three 
neighboring recording elements were emitting light. 
E4(j) the total luminance of four neighboring recording elements (j-1th, 
jth, j+1th and j+2th elements) were measured on condition that the four 
neighboring recording elements were emitting light. 
A light receiving sensor large enough to measure the luminance of the four 
elements simultaneously was used. 
2) The above measurement was conducted for each element sequentially under 
control of the light receiving sensor driving system 61 on the basis of 
the light receiving sensor control section 61. 
3) In the correction data calculating section 68, the calculating process 
was conducted on the basis of the measurement values (E1(j), E2(j), E3(j), 
E4(j)), the luminance (E128(j)) of a single recording element was obtained 
on condition that all elements in the chip were emitting light 
simultaneously. 
In this example, the following calculating processes were conducted: 
E1(j) was assumed as the reference and light amount change rate R2(j), 
R3(j), R4(j) were obtained as shown in FIG. 12. 
EQU R2(j)=(E2(j)-(E1(j)+E1(j+1)))/(E1(j)+E1(j+1)) 
EQU R3(j)=(E3(j)-(E1(j-1)+E1(j)+E1(j+1)))/(E1(j-1)+E1(j)+E1(j+1)) 
EQU R4(j)=(E4(j)-(E1(j-1)+E1(j)+E1(j+1)+E1(j+2)))/(E1(j-1)+E1(j)+E1(j+1)+E1(j+2 
)) 
Each of light amount change rates R2(i), R3(i) and R4(i) were subjected to 
the regression process with a second order function so as to obtain A(2), 
A(3) and A(4). 
EQU R2(X)=A(2).times.X.sup.2 +B(2).times.X+C(2) 
EQU R3(X)=A(3).times.X.sup.2 +B(3).times.X+C(3) 
EQU R4(X)=A(4).times.X.sup.2 +B(4).times.X+C(4) 
The regression process was conducted with a natural logarithm function 
(A(y)=dx1n(y)+h) so as to obtain A(128). 
On the condition that all elements in the chip were emitting light, the 
light amount change rate R128(X)=A(128).times.X**2+B(128).times.X+C(128) 
and its inclination S(128)=2.times.A(128).times.X+B(128) were assumed to 
be 0(zero) around the center (X=63), and B(128) and C(128) were thus 
obtained. 
The correction value (C(i)) for the deviation among pixels were calculated 
with the use of the obtained light amount change rate 
R128(X)=A(128).times.X.sup.2 +B(128).times.X+C(128). 
(j: element No. in the chip) 
j=1 to 32 C(i)=1/(E1(j).times.R128k(32)) 
j=33 to 96 C(i)=1/(E1(j).times.R128k(j)) 
j=97 to 128 C(i)=1/(E1(j).times.R128k(97)) 
4) The above correction value was obtained for each chip, whereby the 
correction value (Ci) was obtained for each element and stored in the 
correction memory 66. 
5) On the basis of the obtained correction value (Ci), the correction was 
conducted in the same way of Comparative Example 1, and the image for the 
evaluation was outputted. 
For the obtained image, the same evaluation of Inventive Example 1 was 
conducted. 
As a result, with regard to Image A for the evaluation, Inventive Example 7 
showed less unevenness even in terms of small-pitch unevenness and a more 
uniform image in each density in comparison with Inventive Example 6. 
Further, with regard to Image B, Inventive Example 7 showed a higher 
quality image with less unevenness in terms of smaller-pitch unevenness 
and good continuous gradation in the gradation of the background and in 
the skin of the person in comparison with Inventive Example 6. 
In Inventive Example 7, with the calculating process, the luminance of a 
single recording element was obtained on the condition that all elements 
in the chip were emitting light simultaneously. However, the luminance of 
a single recording element may be obtained on a similar condition of an 
actually image-outputting condition that plural elements in the chip are 
emitting a light simultaneously. As a result, the same effects can be 
obtained. 
Further, the type of the calculating process is not limited to above 
example. With a proper calculating process in accordance with the 
characteristic of a used-array light source, the luminance of a single 
recording element may be obtained on condition that plural elements in the 
chip are emitting a light simultaneously. Whereby the same effects can be 
obtained. For example, for the portion to be subjected to the regression 
process with a second order function or a natural logarithm function, a 
proper function may be used in accordance with the characteristic of the 
used array light source. 
Still further, in Inventive Example 7, the correction value (Ci) for each 
element was obtained by subjecting the measurement value obtained on 
condition that No. 2, 3, 4 neighboring elements were emitting a light 
simultaneously to the calculating process with the use of the measurement 
value obtained on the condition that a single element was emitting light. 
However, by obtaining the correction value (Ci) for each element by 
subjecting the measurement value obtained on the condition that plural 
elements are emitting light simultaneously to the calculating process with 
the use of the measurement value obtained on the condition that a single 
element was emitting light, the same effects can be obtained. 
Inventive Example 8 
In stead of correction data calculating means of the abovementioned 
Examples on the basis of light amount measurement by receiving light 
sequentially with recording head 30, correction amount was calculated on 
the basis the following method, correction was conducted, and then the 
same image evaluation as that in Inventive Examples 3 and 4 was conducted. 
Correcting Method 8-1 
In LED array of red light source recording head 30a, a correction was 
conducted by the following procedure and recording images 1 and 2 were 
obtained. 
1) While adjoining 2 recording elements (the i th and the i+1 in recording 
elements) were emitted, the total brightness (E.sub.i, i+1) of the 2 
recording elements was measured by a light receiving sensor 55. 
2) While two recording elements in every 2 recording elements (the i th and 
the i+2 th recording elements) were emitted, the total brightness 
(E.sub.i, i+2) of the 2 recording elements was measured by a light 
receiving sensor 55. 
3) Measurements in the above 1) and 2) were successively conducted on each 
recording element under the control by a light receiving sensor driving 
system 62 on the basis of a light receiving sensor control section 61. 
4) By conducting the following calculation process for the measurement 
value in the correction data calculating section 68, a rough calculation 
brightness (Ei) was obtained for each recording element. 
EQU E.sub.i =(E.sub.i-1, i +E.sub.i, i+1 -E.sub.i-1, i+1)/2 
5) Correction data (C.sub.i) was calculated according to a ratio of the 
brightness of the obtained brightness (E.sub.i) and the reference 
brightness (E.sub.0) (an averaged value of all brightness values), and was 
stored in the correction memory 66. 
EQU Ci=E.sub.0 /E.sub.i 
6) An image is formed in the same manner as in Inventive Example 3 and 4 
on the basis of the obtained correction data (C.sub.i). 
Incidentally, a sensor was used, which had a measuring area and a measuring 
range sufficient to measure the brightness of the 2 recording elements 
without decreasing the brightness. 
Correcting Method 8-2 
In LED array of red light source recording head 30a, a correction was 
conducted as same as that in Inventive Example 7 and recording image was 
formed and evaluation was conducted with the same manner as that in 
Inventive Examples 3 and 4. 
In this connection, as the sensor, a sensor was used, which has a measuring 
area and a measuring range sufficient to measure the brightness of 4 
recording elements without decreasing the brightness. FIG. 12 shows an 
example of the changing ratio of the light amount according to the example 
of this experiment. 
As a result of evaluation of the image, in correcting method 8-1, formed 
images 1 and 2 indicated high quality image having fewer density 
unevenness than Inventive Examples 3 and 4 within a gradation level range 
of the present invention, in particular, fewer relatively large 
irregularities on the whole. Further, in correcting method 8-2, an 
excellent image was obtained in which the density unevenness was less than 
in correcting method 8-1, and specifically, fine pitch irregularities was 
fewer. 
Inventive Example 9 
The correction was conducted in the following procedure in VFPH in which 
yellow filter being the green light source printing head 30b was arranged, 
and images A and B for the evaluation were outputted. 
1) On condition that all recording elements were emitting light, the light 
receiving element 55 measured the luminance (Ei) of a single recording 
element (ith element). The light receiving element was sheltered with the 
aperture so as not to receive a light from the other element and a sensor 
capable of measuring only a light from a pixel to be measured was used. 
2) The above measurement was conducted for each element sequentially under 
control of the light receiving sensor driving system 61 on the basis of 
the light receiving sensor control section 61. 
3) A correction value (Ci) was calculated from the luminance ratio of a 
reference luminance data (Eo: the average value of all summed-up luminance 
data) to the obtained luminance data (Ei), and the correction value was 
stored in the correction memory 66. 
EQU Ci=Eo/Ei 
4) The image data to be evaluated were multiplied with the correction data 
by the multiplier 41, and the printing paper 2 was exposed with the 
corrected image data. 
5) The exposed printing paper was subjected to a predetermined developing 
process, whereby the image data to be evaluated was obtained. 
Comparative Example 3 
The correction was conducted in the following procedure in VFPH in which 
yellow filter being the green light source printing head 30b was arranged, 
and images A and B for the evaluation were outputted. 
1) On condition that only a single element was emitting light, the light 
receiving element 55 measured the luminance (Ei). 
2) The above measurement was conducted for each element sequentially under 
control of the light receiving sensor driving system 61 on the basis of 
the light receiving sensor control section 61. 
3) On the basis of the obtained luminance (Ei), the correction was 
conducted in the same way as Comparative Example 1, and the image for the 
evaluation was outputted. 
As a result, with regard to both Image A and Image B for the evaluation, 
Inventive Example 9 showed a high quality image which was less unevenness, 
uniform and good continuous gradation in comparison with Comparative 
Example 3. 
Inventive Example 10 
Instead of correction data calculating means of the abovementioned Examples 
on the basis of light amount measurement by receiving light sequentially 
with recording head 30, correction amount was calculated on the basis the 
following method, correction was conducted, and then the same image 
evaluation as that in Inventive Examples 3 and 4 was conducted. 
Correcting Method 10 
In VFPH in which an yellow filter of a green recording head 30b, a 
correction was conducted in the following manner and forms images 1 and 2 
were obtained. 
The brightness (Ei) of one recording element (the i th element) was 
measured by a light receiving sensor 55 under the condition of light 
emission of all recording elements. As the light receiving sensor 55, a 
sensor was used which can effectively receive the light from one recording 
element to be measured, by using an aperture so that the sensor was not 
affected by the light from the other recording elements. 
2) The above measurement was successively carried out for each recording 
element under the control by a light receiving sensor driving system 62 on 
the basis of a light receiving sensor control section 61. 
Correction data (C.sub.i) was calculated from the brightness ratio of the 
obtained brightness (E.sub.i) to the reference brightness (E.sub.0) (an 
average value of all brightness values), and is stored in the correction 
memory 66. 
EQU Ci=E.sub.0 /E.sub.i 
4) The image formation was carried out by the same method as in Inventive 
Examples 3 and 4, on the basis of the obtained correction data (C.sub.i). 
As a result of evaluation of the image, within a gradation level range of 
the present invention, formed images 1 and 2 both indicated high quality 
image having fewer relatively large irregularities on the whole, fewer 
fine pitch irregularities and fewer density unevenness than Inventive 
Examples 3 and 4. 
In Inventive Examples 9 and 10, the sensor which was shielded from light by 
an aperture was used. However, with another methods of preventing a 
measurement from being influenced by light emitted from other sensors, 
such as a method of using a sensor having high directivity, a method of 
collecting light by using a lens, or a method of introducing light of only 
a specific pixel by using a optical fiber, a similar effect may be 
obtained. 
Inventive Example 11 
The correction was conducted in the following procedure in VFPH in which an 
LED array being a red light source printing head 30a and a yellow filter 
being the green light source printing head 30b were arranged and in VFPH 
in which a blue filter being the blue light source printing head 30c was 
arranged, and the image B for the evaluation was outputted. 
The correction was conducted for the printing heads 30a, 30b and 30c in the 
same way as Inventive Example 2, and the image for the evaluation was 
outputted. 
Comparative Example 4 
The correction was conducted for printing heads 30a, 30b and 30c in the 
same way as Comparative Example 2, and the image for the evaluation was 
outputted. 
The visual evaluation was conducted for the obtained images in terms of 
density unevenness and gradation. 
As a result, in comparison with Comparative Example 4, Inventive Example 11 
showed a high quality image which had less unevenness and better 
continuous gradation in gradation of the background and in the skin of the 
person. 
Inventive Example 12 
The correction was conducted for a printing head 30a by the same manner as 
in Inventive Example 9, for printing head 30b and 30c by the same manner 
as in Inventive Example 7, and an image for evaluation was outputted. 
Comparative Example 5 
The correction was conducted for printing heads 30a, 30b and 30c in the 
same way as Comparative Example 3, and the image for evaluation was 
outputted. 
The visual evaluation was conducted for the obtained images in terms of 
density unevenness and gradation. 
As a result, in comparison with Comparative Example 5, Inventive Example 12 
showed a higher quality image which was less unevenness and better 
continuous gradation in gradation of the background and in the skin of the 
person. 
Inventive Example 13 
A LED array of a red recording head 30a, a VFPH in which a yellow filter of 
a green recording head 30b was arranged and a VFPH in which a blue filter 
of a blue recording head 30c was arranged, were respectively corrected by 
using the method described in Inventive Examples 5, 8 and 10, and a formed 
image 2 was outputted by three color exposures. The same effect could be 
obtained over a gradation level range of the present invention. 
Further, in the above case, when a natural image, such as the formed image 
2, was formed, the most conspicuous effect could be attained in the case 
where the present invention was applied for the green record in g head. 
In Inventive Examples 3, 4, 5, 8, 10, 11, 12 and 13, the density 
measurement and the luminance measurement were taken as examples, the 
combination of the density measurement and the luminance measurement may 
be used. Further, the density measuring means and the luminance measuring 
means may be incorporated into the image forming apparatus, or correction 
data may be calculated at the outside, stored in a memory and used from 
the memory without incorporating the density measuring means and the 
luminance measuring means in the image forming apparatus. 
The same kind of array light source described here, shows an array light 
source in which characteristics of light emission is approximately similar 
to each other when a plurality of recording elements emit the light. 
Examples (a) and (b) of the same kind of array light sources are shown in 
FIG. 13. 
In the above Examples, the correction process was conducted by multiplying 
the correction value. However, the correcting method is not limited to 
this example. Correction by addition, subtraction and dividing may obtain 
the same result. 
In the above Examples, the arrays in which the recording elements were 
aligned in a single line was used. However, with an array in which the 
recording elements are arranged in plural lines, if the exposure control 
is conducted so as to take proper timing between the image forming 
position of the printing head and the recording position on the 
photosensitive material, the same effects can be obtained. 
In the three color exposures mentioned before, an enable signal of each bit 
of blue, green and red is adjusted so as to conform with a gradation 
characteristics and a sensitivity of each light sensitive layer of a 
silver halide light sensitive material, and each recording element is 
driven respectively so as to conduct On-Off recording plural times in 
accordance with the enable signal. Accordingly, it may be preferable, 
because a continuous gradation image having high resolution can be 
recorded on a silver halide light sensitive material by utilizing the 
characteristics of the silver halide light sensitive material without 
causing the apparatus to be complicate and high cost. 
In the above Examples, as means for obtaining the correction value, an 
example using an array to be corrected was used was taken. However, as 
another example, in the event that the deviation of each recording element 
in the array in terms of light emission characteristics shows 
approximately the same characteristics in the same type of array, the 
correction value was obtained in advance with the use of another array of 
the same type, and then the correction may be conducted with the use of 
the correction value. By this way, the array to be corrected may be 
different from the array with which the correction value is obtained. 
Incidentally, in the present embodiment, the enable signals were set in 
accordance with the weight of each bit at the time that the image data are 
represent by a binary value with the use of a binary value type light 
source. However, with the use of the multi value type light source, the 
enable signal may be set in accordance with it. For example, a technique 
in which an enable signal of double time exposure is set for each 
recording element with a light source capable of controlling 16 levels (4 
bits) so that the gradation can be controlled at 256 levels may be 
considered. Further, an appropriate enable signal may be set with the use 
of a light source with which the luminance of the emitting light can be 
changed in addition to a light emitting time period, as the multi-value 
type light source. 
In this embodiment, since the interval between the enable signals is set 
not smaller than 2 s, the influence of the history of the light emission 
caused by the previous enable signal can be reduced, the gradation 
characteristics can be controlled by the time period of the enable signal. 
In case that the interval time is shorter than 2 s, the physical condition 
of the recording element or the photosensitive material between the 
previous light emission and the next light emission does not follow 
completely to On-Off operation due to its characteristics. As a result, 
the above physical condition becomes closer to the condition that light is 
continuously emitted, a stand-up pattern of the emitting light of the 
recording element may differ from that of ordinary cases due to the 
influence of the physical change (including a change in temperature) 
caused by the previous light emission, or there may be fear that the 
fluctuation in the uncontrollable exposure effect may appear. In the case 
that the interval time is not shorter than 2 s, the above influence 
becomes extremely small. 
Inventive Example 14 
FIG. 6 is a view showing the size of pixels to be exposed on printing 
paper. Light emitted from each element of the recording element array 34 
is focused on the printing paper 2 through a Selfoc lens array 35. Now, 
with respect to the arranging direction of the recording element array 34, 
the exposure size of each pixel is defined as "a" and the recording pitch 
is defined "b". On the other hand, with respect to the vertical direction 
(a scanning direction), the exposure size of each pixel is defined as "A" 
and the recording pitch is "B". In condition of the above definition, an 
experiment was conducted in order to investigate the influence on the 
image quality by the exposure size and the recording pitch. A correction 
amount in the exposure amount of each recording element was obtained in 
the manner of the Inventive Examples mentioned above. 
Initially, the exposure size and the recording pitch of each recording 
element array 34 was set as indicated below, and a wedge pattern with the 
gradation of 0 to 255 was exposed and outputted for each color using the 
method explained in FIG. 5. 
______________________________________ 
Red Green Blue 
______________________________________ 
Arranging Direction: 
Exposure Size (a) 
55 50 50 
Recording Pitch (b) 
62.5 62.5 62.5 
Scanning Direction: 
Exposure Size (A) 
35 35 35 
Recording Pitch (B) 
62.5 62.5 62.5 
(unit: .mu.m) 
______________________________________ 
As a result, as shown in FIG. 8, with regard to the wedge of magenta by the 
green exposure, the wedge of cyan by the red exposure and the wedge of 
yellow by the blue exposure, the test result that the density 
characteristics were equal and that smooth continuous gradation was 
reproduced were respectively obtained. 
Further, the exposure size and the recording pitch in relation to the 
arranging direction were changed as indicated below and the exposure size 
and the recording pitch in relation to the scanning direction were set to 
the same conditions as above. 
______________________________________ 
Red Green Blue 
______________________________________ 
Arranging Direction: 
Exposure Size (a) 
40 35 35 
Recording Pitch (b) 
62.5 62.5 62.5 
(Unit: .mu.m) 
______________________________________ 
In this case, discontinuous gradation was observed in low density portions 
and maximum saturated density became a slightly lower density than solid 
black due to the presence of the irregular white. 
Further, the exposure size and the recording pitch in relation to the 
arranging direction were changed as indicated below and the exposure size 
and the recording pitch in relation to the scanning direction were set to 
the same condition as above. 
______________________________________ 
Red Green Blue 
______________________________________ 
Arranging Direction: 
Exposure Size (a) 
82 82 82 
Recording Pitch (b) 
62.5 62.5 62.5 
(Unit: .mu.m) 
______________________________________ 
In this case, the area exposed by a single element became large, resulting 
in the test result that depicting capability for fine patterns was lowered 
and sharpness was also lowered. 
Still further, the exposure size and the recording pitch were changed as 
indicated below: 
______________________________________ 
Red Green Blue 
______________________________________ 
Arranging Direction: 
Exposure Size (a) 
55 50 50 
Recording Pitch (b) 
62.5 62.5 62.5 
Scanning Direction: 
Exposure Size (A) 
15 12 12 
Recording Pitch (B) 
62.5 62.5 62.5 
(unit: .mu.m) 
______________________________________ 
In this case, the irregular white occurred in the high density portion, 
resulting in the test result that the maximum saturated density was 
slightly lowered. 
Still further, the exposure size and the recording pitch were changed as 
indicated below: 
______________________________________ 
Red Green Blue 
______________________________________ 
Arranging Direction: 
Exposure Size (a) 
55 50 50 
Recording Pitch (b) 
62.5 62.5 62.5 
Scanning Direction: 
Exposure Size (A) 
75 75 75 
Recording Pitch (B) 
62.5 62.5 62.5 
(unit: .mu.m) 
______________________________________ 
In this case, overlapping among pixels was caused, resulting in the test 
result that the visual density increased slightly when On-Off recording 
was repeated for each line. 
Further the correction for a light amount of each recording element was 
conducted in the same manner as in Inventive Example 13, a size of a 
recording element array 34 for each color and a recording pitch were set 
as shown in Table 4, and an experiment was conducted in the same manner as 
the above Example except that a wedge pattern having gradation levels of 0 
to 4095 for each color is exposed and outputted by the method explained in 
FIG. 14. 
TABLE 4 
______________________________________ 
Recor- Pixel arrangement 
ding a b a/b A B A/B 
No. head (.mu.m) (.mu.m) 
(.mu.m) 
(.mu.m) 
(.mu.m) 
(.mu.m) 
______________________________________ 
1 Red 40.0 62.5 0.64 35.0 62.5 0.56 
Green 35.0 62.5 0.56 35.0 62.5 0.56 
Blue 35.0 62.5 0.56 35.0 62.5 0.56 
2 Red 50.0 62.5 0.80 35.0 62.5 0.56 
Green 45.0 62.5 0.72 35.0 62.5 0.56 
Blue 45.0 62.5 0.72 35.0 62.5 0.56 
3 Red 75.0 62.5 1.20 35.0 62.5 0.56 
Green 70.0 62.5 1.12 35.0 62.5 0.56 
Blue 70.0 62.5 1.12 35.0 62.5 0.56 
4 Red 85.0 62.5 1.36 35.0 62.5 0.56 
Green 80.0 62.5 1.28 35.0 62.5 0.56 
Blue 80.0 62.5 1.28 35.0 62.5 0.56 
5 Red 55.0 62.5 0.88 15.0 62.5 0.24 
Green 50.0 62.5 0.80 15.0 62.5 0.24 
Blue 50.0 62.5 0.80 15.0 62.5 0.24 
6 Red 50.0 62.5 0.80 55.0 62.5 0.88 
Green 45.0 62.5 0.72 55.0 62.5 0.88 
Blue 45.0 62.5 0.72 55.0 62.5 0.88 
7 Red 55.0 62.5 0.88 70.0 62.5 1.12 
Green 50.0 62.5 0.80 70.0 62.5 1.12 
Blue 50.0 62.5 0.80 70.0 62.5 1.12 
______________________________________ 
As can be seen from the above test results, when the ratio of the exposure 
size in the recording element arranging direction to the recording pitch 
in the recording element arranging direction is in the range of 0.7 to 
1.2, and the ratio of the exposure size in the vertical direction in the 
recording element arrangement to the recording pitch in the vertical 
direction is in the range of 0.3 to 1.0, continuous gradation 
characteristics is obtained. 
Further, under the above condition, a wedge pattern for each color and a 
natural image like the formed image 2 in the beforementioned Example were 
outputted and the evaluation was conducted visually. As a result, in Nos. 
2, 3 and 6, high quality images excellent in rough texture in comparison 
with Nos. 1 and 5 and in sharpness in comparison with Nos. 4 and 7 could 
be obtained. Further, in Nos. 2, 3 and 6, it became possible to depict a 
continuous gradation whose density change is smooth for gradation change. 
Further, the exposure size and the recording pitch were set as indicated 
below: 
______________________________________ 
Red Green Blue 
______________________________________ 
Arranging Direction: 
Exposure Size (a) 
55 50 50 
Recording Pitch (b) 
62.5 62.5 62.5 
Scanning Direction: 
Exposure Size (A) 
35 35 35 
Recording Pitch (B) 
62.5 62.5 62.5 
(unit: .mu.m) 
______________________________________ 
On the above condition, the experiment was conducted in such a manner that 
the ratio C of the time period from the starting of the light emission to 
the ending of the light emission for one line to the recording time cycle 
for the one line was changed to 4 cases as indicated below: 
(a) C=0.18, (b) C=0.3, (c) C=0.68, and (d) C=0.8 
The following test results were obtained: 
In the case of (a), irregular white occurred in a high density portion and 
the maximum saturated density was slightly lowered. In the case of (b), 
the depicting capability for fine patters were lowered. On the other hand, 
in the cases of (c) and (d), a smooth continuous gradation was obtained 
without the above problems. 
As can be seen from the above results, with the recording conducted so as 
to satisfy the relationship of 0.8.ltoreq.(A/B+C).ltoreq.1.3, continuous 
gradation characteristics were obtained. 
Moreover, an enable signal was changed in accordance with formula (2.sup.n 
T+t) in the generating section of the enable signal for each color, 
wherein "n" is either 0, 1, 2, . . . or 7 and represents bit No. of a 
digital value in the case that the time period of the enable signal was 
converted into a digital value in accordance with the gradation of the 
image data, "T" is a unit of time, and "t" is a time constant of either 
positive or negative value. 
______________________________________ 
t = 3 t = 5 t = 8 
B G R 
______________________________________ 
MSB 1539 2565 5128 
2nd bit 771 1285 2568 
3rd bit 387 645 1288 
4th bit 195 325 648 
5th bit 99 165 328 
6th bit 51 85 168 
7th bit 27 45 88 
LSB 15 25 48 
(Unit: .mu.s) 
______________________________________ 
In this case, since the time period of the enable signal could be adjusted 
individually for each signal for each count value as shown with the wedge 
density characteristics of magenta by the green exposure in FIG. 9, each 
measuring point could be made continuous or equal so that smoother 
gradation recording could be conducted. Incidentally, with regard to the 
cyan wedge by the red exposure and the yellow wedge by the blue exposure, 
the same results as above were obtained. 
In the case that, among a generating period of an enable signal for each 
color, a generating period in the red recording is determined as shown 
below by changing an enable signal in 2.sup.n T+t (n is 0, 1, 2, - - - 11 
and represents a figure of a digital value when an each time width of the 
enable signal is made in the digital value in accordance with the 
gradation of an image data, T is a unit time, and t is a given positive 
time or a negative given time and is 0.4 .mu.sec. in this experiment), 
since the time width of the enable signal can be adjusted respectively for 
each signal for each counter value as shown by a wedge density 
characteristics of a cyan color by a red color exposure in FIG. 16, each 
measuring point becomes continuous or equivalent so that smooth gradation 
recording can be conducted. 
______________________________________ 
MSB 205.2 
2nd bit 
102.8 
3rd bit 
51.6 
4th bit 
26.0 
5th bit 
13.2 
6th bit 
6.8 
7th bit 
3.6 
8th bit 
2.0 
9th bit 
1.2 
10th bit 
0.8 
11th bit 
0.6 
LSB 0.5 
______________________________________ 
As indicated above, in a conventional technique, a neutral color balance 
was slightly changed depending on the density due to the discontinuity in 
gradation depending on the responding characteristics of the recording 
element and the characteristics of the photosensitive material. However, 
in the embodiment of the present invention, the gradation becomes 
continuous and smooth gradation can be obtained, resulting in neutral 
ability being improved and the image quality being enhanced. 
FIG. 7 is a timing chart showing another embodiment for the output signal 
from the printing head controlling section 40. 
In this embodiment, there is provided a "n" order counter (for example "n" 
=256 in the case of 256 gradation) to drive the recording element by the 
number of times in accordance with the density of each pixel. The count 
value is compared with the density value of each pixel. When the density 
value is larger, "1" signal is transmitted to shift register 31 so that 
the driving signal is made in its active condition during that time. On 
the other hand, when the density is smaller, "0" signal is transmitted and 
the active condition is ended so that only the driving signal 
corresponding to the density of the pixel becomes an allowable condition. 
Then, the light emission control is conducted in such a way that a unit 
time during which the driving signal becomes active for each time is 12 
.mu.s for blue, 20 .mu.s for green, and 40 .mu.s for red. In other words, 
in the case of 256 gradations, the gradation is depicted by generating the 
enable signal 256 times for each pixel. With this technique, the test 
result that the same wedge density characteristics of magenta by the red 
exposure as shown in FIG. 8 could be obtained was acknowledged. 
Incidentally, with regard to the cyan wedge by the red exposure and the 
yellow wedge by the blue exposure, the same results were be obtained. 
In this way, according to this embodiment, it is not necessary to set an 
enable signal for each bit, and good gradation can be obtained with rather 
simple construction. 
FIG. 17 is a timing chart showing another embodiment of an output signal 
from recording head control section 40. 
A light emission control is conducted so that a unit time in which a drive 
signal becomes active is 0.3 .mu.sec for blue, 0.3 .mu.sec for green and 
0.1 sec for red for each time. Accordingly, in the case of 256 levels in 
gradation, enable signals are generated 256 times so as to depict the 
gradation. With this method, a wedge density characteristics of magenta 
coloring by a green exposure, a wedge of magenta coloring by a red 
exposure and a wedge density characteristics of yellow coloring by a blue 
exposure are obtained as same as above. 
Further, in cases that a generating period of the enable signal is changed 
for each color in accordance with a count value of the "n" order counter 
in the manner indicated below, the gradation levels in the low density 
become continuous. As a result, test results in which smooth continuous 
gradation can be reproduced as indicated with the wedge density 
characteristics of magenta coloring by green exposure in shown in FIG. 10 
was obtained. 
______________________________________ 
Counter value 
Period 
______________________________________ 
For green 
0 1 .times. 14.5 .mu.s 
1 (10.sup.0.01 - 1) .times. 14.5 
.mu.s 
2 (10.sup.0.02 - 10.sup.0.01) .times. 14.5 
.mu.s 
3 (10.sup.0.03 - 10.sup.0.02) .times. 14.5 
.mu.s 
-- -- 
-- -- 
i (10.sup.0.01i - 10.sup.0.01(i - 1)) .times. 14.5 
.mu.s 
-- -- 
-- -- 
255 (10.sup.2.55 - 10.sup.2.54) .times. 14.5 
.mu.s 
For blue 
0 1 .times. 8.7 .mu.s 
1 (10.sup.0.01 - 1) .times. 8.7 
.mu.s 
2 (10.sup.0.02 - 10.sup.0.01) .times. 8.7 
.mu.s 
3 (10.sup.0.03 - 10.sup.0.02) .times. 8.7 
.mu.s 
-- -- 
-- -- 
i (10.sup.0.01i - 10.sup.0.01(i - 1) .times. 8.7 
.mu.s 
-- -- 
-- -- 
255 (10.sup.2.55 - 10.sup.2.54) .times. 8.7 
.mu.s 
For red 
0 1 .times. 29 .mu.s 
1 (10.sup.0.01 - 1) .times. 29 
.mu.s 
2 (10.sup.0.02 - 10.sup.0.01) .times. 29 
.mu.s 
3 (10.sup.0.03 - 10.sup.0.02) .times. 29 
.mu.s 
-- -- 
-- -- 
i (10.sup.0.01i - 10.sup.0.01(i - 1)) .times. 29 
.mu.s 
-- -- 
-- -- 
255 (10.sup.2.55 -10.sup.2.54) .times. 29 
.mu.s 
______________________________________ 
Incidentally, with regard to the cyan wedge by the red exposure and the 
yellow wedge by the blue exposure, the same test results were obtained. As 
mentioned above, according to the present embodiment, since the width of 
the enable signal can be freely changed, the gradation can be adjusted in 
accordance with the output characteristics of the apparatus and the 
characteristics of the photosensitive material. 
In the case that a generating period of an enable signal was changed for 
the count value of n-order counter with regard to each of green, blue and 
red as shown in Table 5, gradation level in a low density region became 
continuous. As a result, an experiment result reproducing a smooth 
continuous gradation could be obtained as shown by the wedge density 
characteristics of magenta coloring by a green exposure shown in FIG. 18. 
TABLE 5 
______________________________________ 
Count 
value 
of 
n-order 
Enable signal generating period (.mu.s) 
counter 
Green Blue Red 
______________________________________ 
0 1 .times. 2.0 
1 .times. 2.0 
1 .times. 1.0 
1 (10.sup.0.01 - 
(10.sup.0.01 - 
(10.sup.0.01 - 1) .times. 1.0 
1) .times. 2.0 
1) .times. 2.0 
2 (10.sup.0.02 - 
(10.sup.0.02 - 
(10.sup.0.02 - 10.sup.0.01) .times. 1.0 
10.sup.0.01) .times. 2.0 
10.sup.0.01) .times. 2.0 
3 (10.sup.0.03 - 
(10.sup.0.03 - 
(10.sup.0.03 - 10.sup.0.02) .times. 1.0 
10.sup.0.02) .times. 2.0 
10.sup.0.02) .times. 2.0 
i (10.sup.0.011 - 
(10.sup.0.011 - 
(10.sup.0.011 - 10.sup.0.01(i - 
10.sup.0.01(i - 1)) .times. 2.0 
10.sup.0.01(i - 1)) .times. 2.0 
1)) .times. 1.0 
255 (10.sup.2.55 - 
(10.sup.2.55 - 
(10.sup.2.55 - 10.sup.2.54) .times. 1.0 
10.sup.2.54) .times. 2.0 
10.sup.2.54) .times. 2.0 
______________________________________ 
Incidentally, the same results were obtained in a wedge of cyan coloring by 
a red exposure, a wedge of yellow coloring by a blue exposure. 
In the above embodiment, a LED recording head and a VFPH recording head 
were used. However, a head for exposure is not limited to these heads. The 
similar effect may be obtained by a recording head which comprises a 
plurality of recording elements and can turn each recording element On or 
Off independently of others, such as a PLZ recording head using an 
appropriate back light, a light shutter array like a liquid shutter array 
recording head, and a laser array recording head in which semiconductor 
laser are arranged in an array form. 
In the above embodiment, an image is formed by moving a light sensitive 
material for recording elements. However, it may be possible to form an 
image by moving recording elements for a light sensitive material. 
In an image forming apparatus shown in FIG. 19, light emitted from a single 
light source 3 switched On during an image formation is divided by optical 
fibers 36, introduced into PLZT recording heads 37a, 37b and 37c equipped 
with a color filter, and used by recording heads 37a, 37b and 37c so as to 
expose a photographic paper 2 of a silver halide light sensitive material 
conveyed by nipping conveyance rollers in the same way as red, green and 
blue recording heads 38a, 38b and 38c shown in FIG. 1 so that the same 
result can be obtained. 
Further, in an image forming apparatus shown in FIG. 20, a head carrier 38 
on which a small width recording head of red 38a, 38b and 38c are mounted 
is shifted in a width direction by a conveying screw 5 driven by a motor 
4, thereby conducting exposure overall a photographic paper having a large 
width with the small width recording head 38a, 38b and 38c so that the 
same high quality image formation as the image forming apparatus shown in 
FIGS. 1 and 19 can be conducted. 
A recording head 30 shown in FIG. 21 is composed of a recording element 
array 34a in which recording elements are arranged alternately in 
staggered two lines and a Selfoc lens array 35a for focusing light emitted 
from each recording element as an image on a silver halide light sensitive 
material. A recording head 30 shown in FIG. 22 is composed of a recording 
element array 34b in which recording elements are arranged in panel-shaped 
four lines and a Selfoc lens array 35b for focusing light emitted from 
each recording element as an image on a silver halide light sensitive 
material. By using these recording heads 30, an image formation can be 
conducted at a higher speed than the recording head 30 shown in FIG. 6. 
Further, in the time period necessary from the start of the light emission 
to the end of the light emission for one line during which the exposure 
was conducted while the shift and stop of the printing paper was repeated, 
the test was conducted by changing the ratio "r.sub.t " of the time period 
of the shift was changed to 50% and 30% . In the time of "r.sub.t "=30% , 
an irregularity was observed in the image. On the other hand, in the time 
of "r.sub.t "=50% , the density in each pixel region was unified, no 
irregularity was observed, and further, the density, in each pixel region 
did not become the saturated density from the low image density level. 
Accordingly, test results that the responding ability for the gradation 
was improved so as to attain good gradation was obtained. 
As explained above, with Methods 1 and 2 and Structures 1 and 2, on the 
condition that a plurality of recording elements are driven and that the 
recording condition is close to an actual image recording condition, a 
light amount is obtained and correction is conducted, whereby density 
unevenness caused by the deviation in the light emission characteristics 
of each recording element can be reduced, a high resolution continuous 
gradation image can be obtained and a high quality image can be formed, 
without resulting in a complicated expensive apparatus. 
In the invention, since density measurement values can be handled as light 
amount data on condition equal to the condition that the recording 
elements are driven so as to actually output an image, a far better image 
without the density unevenness can be obtained. In the invention, since 
the relationship between the light emission time and the density in the 
case of plural time exposures in which the exposure is conducted plural 
times is obtained and the correction is conducted based on the 
relationship, the density unevenness caused by the discontinuity in the 
relationship between the light emission time and the density can be 
eliminated more precisely and a far better image with less density 
unevenness can be obtained. 
In the invention, since the light amount data are obtained directly on the 
actual image recording condition, the control can be simplified. In 
addition, density unevenness can be reduced so that the high image quality 
can be obtained. 
In the invention, by using the measurement value of a single element 
together, a small density unevenness for each pixel can be reduced in 
addition to the unevenness of a large pitch, so that a high quality image 
can be obtained. 
In the invention, since light measurement for a single element is conducted 
on condition that plural recording elements are emitting light, a 
correction value can be calculated far more precisely, so that a high 
quality image can be obtained. 
In the invention, the driving means conducts the driving for the On-Off 
recording plural times for the silver halide photosensitive material in 
accordance with the time period of the enable signal. Accordingly, 
continuous gradation recording can be conducted so that a high quality 
image can be obtained without causing the apparatus to be complicated and 
a high cost. 
In the invention, since the enable signal for each color can be set to 
conform with the sensitivity and the gradation characteristics of each 
photosensitive layer of the silver halide color photosensitive material, a 
continuous gradation image with a high resolution can be recorded on the 
silver halide color photosensitive material with the utilization of the 
characteristics of the silver halide photosensitive material without 
causing the apparatus to be complicated and a high cost. 
Further, with the effect of the intermittent exposure effect which is the 
characteristics of the silver halide color photosensitive material, the 
difference between the high and low sensitivities becomes large and the 
color cross talk can be reduced so that color separation can be improved. 
In. addition, the spread of dots can be further widened so that the 
density of each dot region can be unified. As a result, a continuous 
gradation recording can be conducted so that a high quality image can be 
obtained without causing the apparatus to be complicated and a high cost 
for the purpose of positional registration for each color. 
In the invention, since the plurality of recording elements arranged in an 
array form of a single line or plural lines is composed of a light 
emitting member comprising an LED array, a vacuum fluorescent tube array 
or a liquid shutter array, the discontinuity of the gradation can be 
reduced. 
As mentioned before, the silver chloride photosensitive material tends to 
cause the density unevenness greatly due to the influence of the 
multi-exposure effect by the plural time exposures or the intermittent 
exposure effect. 
However, in the invention, since the density unevenness is improved 
appreciably, the effect of the present invention for the silver chloride 
photosensitivity material is greater and the developing process can be 
conducted at a high speed. 
In the invention, the enable signal corresponding to the density value of 
the image data can be set without causing the apparatus to be complicated 
at high cost. 
In the invention, since the time period of the enable signal can be 
adjusted respectively by increasing or decreasing "t", the smooth 
gradation recording can be conducted. 
In the invention, the apparatus can be simplified and the similar gradation 
recording can be realized by the simpler structure. 
In the invention, since the time period of the enable signal can be 
adjusted finely, the gradation characteristics can be adjusted in 
accordance with the output characteristics of the apparatus. 
Further, in the invention, more continuous gradation characteristics can be 
obtained. 
In the invention, the gradation characteristics can be controlled with the 
time period of the enable signal. In addition, in cases where the exposure 
is conducted while the shifting is conducted, the unevenness recording 
caused in accordance with the spread of dot in the time of area modulation 
can be reduced. 
In the invention, since the exposure is conducted while the shifting is 
conducted, the density in the dot region can be unified and the responding 
ability in the gradation control can be improved.