Image reading apparatus

An image reading apparatus comprising a lighting control means, an analog shift means, a transfer control means and a clock pulse control means. According to the controlling operation of a lighting control means for lighting the light source during a given time period, the output of the CCD sensor is prohibited from being fed to the analog shift means while the light source is turned on, with the output of the CCD sensor being adapted to be fed to the analog shift means and to shift to an output circuit while the light source is turned off, thus preventing the accumulation of light electric-charges, caused by light leakage within a light-source lighting period, and preventing mixed color reading through the remaining electric charges, with the result that the color resolution of the red, green, blue can be performed with accuracy.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image reading apparatus and more 
particularly, to an image reading apparatus applied to a color scanner, a 
color facsimile or the like, which uses a unit CCD sensor to flash 
sequentially three fluorescent lamps of red, green and blue lights as 
light sources in accordance with the scanning period of the CCD sensor, 
and to detect by the CCD sensor the reflected lights from the image to 
perform the color resolution. 
2. Description of the Prior Art 
Conventionally, FIG. 1 through FIG. 3 show an optical system in an image 
reading apparatus which is the background of this invention, and to which 
one embodiment of the present invention is applied. In an example shown in 
FIG. 1, there are provided an R fluorescent lamp 2 which transmits a red 
light to a color manuscript 1, a G fluorescent lamp 3 which transmits a 
green light thereto, and a B fluorescent lamp 4 which transmits a blue 
light thereto. The reflected lights from the color manuscript 1 in 
accordance with the lights from the fluorescent lamps 2 through 4 are 
focused with a lens 6 from a mirror 5 and are input into the CCD sensor 7. 
In an example shown in FIG. 2, only a fluorescent lamp 8 of ordinary light 
is provided for the color manuscript 1. The reflected light from the color 
manuscript 1 in accordance with the light from the fluorescent lamp 8 is 
reflected by the mirror 5 and is separated into the respective light 
components of the red, green, blue of the color manuscript 1 by a filter 
disk 9 so as to be input into the CCD sensor 7 through the lens 6. 
In an example shown in FIG. 3, a dichroic mirror 10, instead of a filter 
disk 9 shown in FIG. 2, is disposed behind the lens 6 to separate the 
light of the color manuscript 1 into the light components of the red, 
green, blue thereof so as to be respectively input into an R reading CCD 
sensor 11, a G reading CCD sensor 12 and a B reading CCD sensor 13. 
The CCD sensors 7, 11 through 13 shown in the above-described FIG. 1 
through FIG. 3 output light electric-charge from the light incidence. The 
light electric-charge not shown is loaded on an analog shift register and 
is sequentially shifted in accordance with a clock pulse. The electric 
charge caused due to some light leakage is added later while the content 
loaded on the analog shift register is being shifted. Namely, the electric 
charge from the sensor portion to the analog shift register is not 
completely transferred by one shift, thus resulting in some short shipment 
of the remaining load. The above-described two facts are responsible for 
deterioration in the accuracy of the color resolution in the conventional 
image reading apparatus, and measures against them have not been taken at 
all or have been neglected. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide an 
improved image reading apparatus, which is free from the above-described 
problems so that the color resolution of the red, green, blue may be 
performed with accuracy. 
In accomplishing the object of the present invention, according to one 
preferred embodiment of the present invention, there is provided an 
improved image reading apparatus which is adopted to detect by the use of 
a CCD sensor the lights from a light source reflected by images, 
comprising: a lighting control means for lighting said light source only 
during a given period; an analog shift means which receives a plurality of 
analog signals for output in parallel from said CCD sensor and shifts them 
in accordance with a clock pulse; a transfer control means which prohibits 
the CCD sensor outputs from being fed to said analog shift means while 
said light source is turned on, and feeds the CCD sensor outputs to said 
analog shift means while said light source is turned off; a clock pulse 
control means which feeds the clock pulse to said analog shift means to 
perform a control operation for shifting the contents of the analog shift 
means. With this construction, in accordance with the control of the 
lighting control means for turning on a light source only during a given 
period, the output of the CCD sensor is prohibited from being fed to an 
analog shift means while the light source is on, while the transfer is 
controlled so that the output of the CCD sensor may be fed to the analog 
shift means while the light source is off, and the control is performed 
such that a clock pulse is given to the analog shift means to shift the 
contents of the analog shift means.

DETAILED DESCRIPTION OF THE EMBODIMENT 
The entire construction of an image reading apparatus in one embodiment of 
the present invention will be described with reference to FIG. 4. In FIG. 
4, an R fluorescent lamp 13, a G fluorescent lamp 14 and a B fluorescent 
lamp 15 are adapted to illuminate the red, green, blue lights respectively 
on the images. The fluorescent-lamp lighting circuit 16 alternately 
lights, at a constant period, the R fluorescent lamp 13, the G fluorescent 
lamp 14 and the B fluorescent lamp 15 respectively in accordance with 
lighting control signals FLR, FLG and FLB given from a control circuit 17. 
The image reading portion 18, which will be described in detail in FIG. 5 
to be described later, is adapted to read the reflection lights by a CCD 
sensor, which are lights from the R fluorescent lamp 13, the G fluorescent 
lamp 14, and the B fluorescent lamp 15 reflected by the images. A start 
pulse .phi..sub.T, cross pulses .phi..sub.1, .phi..sub.2 and a reset pulse 
.phi..sub.R are fed to the image reading portion 18 from the control 
circuit 17. An image signal VO read out by the image reading portion 18 
is fed to a sample hold circuit 19. A sampling pulse SH is fed from the 
control circuit 17 to the sample hold circuit 19. The sample hold circuit 
19 holds by samples a reading signal VO from the image reading portion 18 
in accordance with this sampling pulse SH. An output signal vo sample-held 
is given to the control circuit 17. 
The detailed construction of the image reading portion 18 shown in the 
above-described FIG. 4 will be described hereinafter with reference to 
FIG. 5. The CCD sensor 181 outputs light electric-charges in accordance 
with the reflected lights from the images. The light electric-charges are 
fed to a transfer gate 182. A start pulse .phi..sub.T is fed to the 
transfer gate 182. The transfer gate 182 transfers to an analog register 
183 the light electric-charges coming from the CCD sensor 181 in 
accordance with the start pulse .phi..sub.T. Clock pulses .phi..sub.1, 
.phi..sub.2 are fed to the analog shift register 183. The analog shift 
register 183 sequentially outputs in accordance with the clock pulses 
.phi..sub.1, .phi..sub.2 the light electric-charges of the CCD sensor 181 
transferred from the transfer gate 182 to feed them to an output buffer 
184. The output buffer 184 sequentially outputs the image data. The light 
electric-charge is reset by the reset pulse and the following light 
electric-charge is received. 
The operation of an image reading apparatus shown in FIG. 4 and FIG. 5 will 
be described hereinafter with reference to FIG. 6 and FIG. 7, showing 
wave-forms of each portion of FIGS. 4 and 5, respectively. A fluorescent 
lamp lighting circuit 16 sequentially flashes an R fluorescent lamp 13, a 
G fluorescent lamp 14, and a B fluorescent lamp 15 in accordance with 
lighting control signals FLR, FLG and FLB to be fed from the control 
circuit 17. Namely, when the lighting control signal FLR becomes "1", the 
R fluorescent lamp 13 lights, when the lighting control signal FLG becomes 
"1", the G fluorescent lamp 14 lights, and when the lighting control 
signal FLB becomes "1", the B fluorescent lamp 15 lights. The reflected 
lights from the images in accordance with the lights from the R 
fluorescent lamp 13, the G fluorescent 14 and the B fluorescent lamp 15 
are detected by the CCD sensor 181. Namely, when the R fluorescent lamp 13 
lights on during a period of a scanning period M shown in FIG. 6, the 
light electric-charges corresponding to the R information of the image are 
accumulated among each regions S.sub.1, S.sub.2, S.sub.3 . . . , 
S.sub.N-1, S.sub.N in the CCD sensor 181. And the light electric charges 
accumulated among the regions S.sub.1, S.sub.2, S.sub.3 . . . , S.sub.N-1, 
S.sub. N of the CCD sensor 181 by a start pulse .phi..sub.T in the 
following scanning period M+1 are loaded on the regions SR, SR.sub.2, 
SR.sub.3 . . . SR.sub.N-1, SR.sub.N of an analog shift register 183 by the 
transfer gate 182. 
The analog shift register 183 transfers the loaded contents to an output 
buffer 184 in accordance with the clock pulses .phi..sub.1, .phi..sub.2. 
The output buffer 184 converts in photoelectricity the light 
electric-charge transferred from the analog shift register 183 and outputs 
it as a CCD output signal VO. It is to be noted that the light 
electric-charges to be transferred sequentially from the analog shift 
register 183 are reset each time within the output buffer 184 by a reset 
pulse .phi..sub.R. Accordingly, as shown in FIG. 6, CCD output signals 
VO.sub.1, VO.sub.2, VO.sub.3 . . . , VO.sub.N corresponding to the light 
electric-charges accumulated on the regions S.sub.1, S.sub.2, S.sub.3 . . 
. S.sub.N are output as shown within the scanning period M+1 of the start 
pulse .phi..sub.T. They are the normal CCD output signals. 
The CCD output signal should be basically "0" in the scanning period M in 
the start pulse .phi..sub.r shown in FIG. 6. However, if the lights are 
illuminated on the chip of the CCD sensor even while the light 
electric-charges are being transferred to the output buffer 184 by an 
analog shift register 183 disposed within the image reading portion 18, 
some lights are incident into the analog shift register 183 to cause light 
electric-charges to add them to the normal light-electric charges, with 
the result that some CCD output signals come. The CCD output signals are 
different in level within the period of the scanning period M. Namely, 
VO.sub.N shows a considerable level of additive light-electric charges 
while the VO.sub.1 is almost "0". This is because it takes a short time 
for the light electric-charge accumulated on the region S.sub.1 of the CCD 
sensor 181 to be transferred to the region SR.sub.1 of the analog shift 
register 183 and to reach the output buffer 184, while for VO.sub.N, it 
takes a time T.sub.1 in FIG. 6 for the light electric-charge accumulated 
on the S.sub.N of the CCD sensor 181 to reach the output buffer from the 
transfer of the light electric-charge to the region SR.sub.N of the analog 
shift register 183 so that the additive effect of the light 
electric-charge due to the light leakage into the analog shift register 
183 is large. It is costly to completely remove such an adding effect as 
described hereinabove. 
In FIG. 5, the accumulated light electric-charges on the sensor portion 181 
are not completely transferred to the analog shift register portion by one 
time period of start pulse .phi..sub.r, thus 3 through 4% of the light 
electric-charges remain. The present invention is provided to prevent 
deterioration in the accuracy of the color resolution, which is caused 
through the adding effect caused by the light electric-charges of the 
incident light which remain in the analog shift register portion and the 
incomplete transfer to the analog shift register portion. 
The operation of one embodiment of the present invention will be described 
hereinafter with reference to FIG. 8 and FIG. 9, showing respectively 
wave-form views of an image reading apparatus. Referring to FIG. 8, the 
control circuit 17 operates at the scanning periods of B.sup.2.sub.M-1, 
R.sup.1.sub.M, M.sup.2.sub.M, G.sup.1.sub.M, G.sup.2.sub.M, B.sup.1.sub.M, 
B.sup.2.sub.m, R.sup.1.sub.M+1, R.sup.2.sub.M+1, G.sup.1.sub.M+1. At the 
scanning periods of R.sup.1.sub.M, G.sup.1.sub.M, and B.sup.1.sub.M, the R 
fluorescent lamp 13, the G fluorescent lamp 14 and the B fluorescent lamp 
15 are sequentially flashed by the fluorescent lamp lighting circuit 16. 
At this time, the output of the CCD sensor 181 is neglected. In the 
embodiment of the present invention, the output signals of the CCD sensor 
181 including the respective pure R information, G information, B 
information which appear at the scanning periods R.sup.2.sub.M, 
G.sup.2.sub.M and B.sup.2.sub.M are used. 
More details will be give with reference to FIG. 9. Among clock pulses for 
transferring the light electric-charges to the output buffer 184 from the 
analog shift register 183 in FIG. 9, a clock pulse at the scanning period 
of a luminous timing is rendered faster than a clock pulse of the reading 
period. The output signal level v.sub.1 of the CCD sensor 181 which 
appears at the scanning period R.sub.M is a short-shipped portion of the 
light electric-charge corresponding to the B information at the former 
period. Also, the level v.sub.2 is an output corresponding to the light 
electric-charge caused by the light leakage into the analog shift register 
183. Light electric-charges caused by some light leakage which remains in 
the regions SR.sub.1, SR.sub.2, . . . SR.sub.N of the analog shift 
register 183 at a time the fluorescent lamp 13 has turned off in the 
scanning period R.sub.M, i.e., at the N+n.sub.2 of the time of the reset 
pulse .phi..sub.R is discharged. This level is SR.sub.1 &gt;SR.sub.2 
&gt;SR.sub.3 &gt; . . . &gt;SR.sub.N .apprxeq.0. To discharge it from the analog 
shift register 183, transfer clock pulses are sent by n.sub.3 portions in 
excess (n.sub.3 =N in this invention) from it even after the R fluorescent 
lamp 13 has been turned off. In addition, to make this time period short, 
the period of the transfer clock pulse in this time period is rendered 
faster. The clock pulse of the scanning period in the respective luminous 
timings of not only the R fluorescent lamp 13, but also the G fluorescent 
lamp 14 the B fluorescent lamp 15 is rendered faster than the clock pulse 
of the reading period. In a time period during which the R fluorescent 
lamp 13, the G fluorescent lamp 14 and the B fluorescent lamp 15 are 
respectively turned on, the light electric-charges from the CCD sensor 181 
are prohibited from being transferred to the analog shift register 183, 
and in a time period during which they are turned off, the light 
electric-charges from the CCD sensor 181 are transferred to the analog 
shift register 183 so that the period of the transfer clock pulse in a 
given time period after the lamps have been turned off is rendered faster 
to discharge the light electric-charges caused by the light leakage 
accumulated on the analog shift register 183, with the result that the 
pure R, G, B which are not mixed in color are outputted as output signals 
corresponding to the R information, G information and B information. 
Thus, in accordance with the present invention, it is so arranged that 
according to the controlling operation of a lighting control means for 
lighting the light source during a given time period, the output of the 
CCD sensor is prohibited from being fed to the analog shift means while 
the light source is turned on, and the output of the CCD sensor is adapted 
to be fed to the analog shift means so as to shift while the light source 
is turned off, thus preventing the accumulation of the light 
electric-charges, which is caused by light leakage within a light-source 
lighting period, and preventing mixed-color reading through the remaining 
electric charges, with the result that the color resolution of the R, G, B 
can be performed with accuracy. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.