JPH04290068A - Image reader - Google Patents

Abstract

PURPOSE:To correct the output level of a CCD by the sensitivity difference of R, G, and B-as making a circuit into common use. CONSTITUTION:An image reader is comprised of a CCD image sensor unit 30 including a CCD image sensor 9 and plural first emitter-followers 12-14., image signal pre-processing circuits 40B, 40G, and 40R, and A/D converters 45B, 45G, and 45R. Means 18-20, Rba-Rbb, Rga-Rgb, and Rra-Rrb which correct the sensitivity difference of R, G, and B are further provided at the unit 30, which enables the output level to be corrected.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides CC
The present invention relates to an image reading device that optically reads data using a D image sensor, and particularly relates to an image reading device using a 3-line color image sensor.

0002

[Prior Art] A CCD 3-line image sensor has three one-dimensional CCD sensors arranged in parallel, and the glass surface is sequentially colored with R (red), G (green), and B (blue) primary color filters. It is a miniature sensor.

FIG. 4 shows the relative sensitivity to the wavelength of incident light when each one-dimensional CCD sensor is colored with a color filter, assuming that each one-dimensional CCD sensor has the same sensitivity when uncolored. This is called the spectral sensitivity characteristic, and the maximum value of the red filter showing the highest sensitivity is set to 1, and the CC with each color filter corresponds to the wavelength of the incident light.
This is a graph of the sensitivity of D.

FIG. 5 shows the spectral distribution of a daylight fluorescent lamp. The spectral distribution is 2 at wavelengths from 450 nm to 600 nm.
It has two peaks and is attenuated around it. Therefore, when a daylight fluorescent lamp is used as a light source for a copying machine, the sensitivity decreases in the order of green, red, and blue. The difference in sensitivity is twice that between green and blue.

[0005] Therefore, if a white document is read as a reference by a CCD 3-line color sensor, R, G, B
The CCD outputs will not be the same. In terms of the three primary colors of light, when reading white, R, G, and B must originally be at the same level, so somewhere we have to account for the difference in sensitivity between R, G, and B of the CCD and the output level difference due to the spectral distribution of the fluorescent lamp. Must be corrected.

Conventionally, this sensitivity difference between R, G, and B has been corrected by an image signal preprocessing circuit. FIG. 6 shows an outline of the configuration of a conventional CCD image sensor unit 60. 9 is a CCD image sensor having B channel, G channel, and R channel; 12, 13, and 14 are low impedance emitter follower transistors for outputting from the CCD image sensor unit 60; 15;
16 and 17 are capacitors for cutting direct current.

Here, the sensitivity of the CCD image sensor 9 to daylight fluorescent lamps is Sb (blue), Sg (green), and Sg.
CC by defining it as r (red) (V/1x・sec)
The illuminance on the D side is Lc (1x), and the accumulation time is t (sec).
Then, the output (V) from the CCD image sensor unit 60 is Vob=Sb×Lc×t (1)
Blue Vog=Sg×Lc×t
(2) Green Vor=Sr×Lc
×t (3) It becomes red. Here, the accumulation time refers to 1 of the CCD image sensor.
This is the period of reading out the main scanning portion, during which charge is accumulated in the light receiving section.

FIG. 7 shows an outline of the configuration of a conventional image signal preprocessing circuit 70. 71 is an inverting amplifier, 72 is a sample hold circuit, 73 is a DC regeneration circuit, 74
is a variable gain amplifier. Further, 76 is an AD converter. The output from the CCD image sensor 9 is input into an inverting amplifier 71 through AC coupling. Here, by inverting the appropriate gain and polarity, the sample and hold circuit 72
The image signal part is sampled. The output of the CCD image sensor 9 before being sampled and held has a repeating waveform of the CCD clock frequency called reset noise. The DC regeneration circuit 73 regenerates the DC component by fixing the output of a portion of the photodetection section called the light shield section of the CCD, which is masked with aluminum, at zero volts as a black level. The variable gain amplifier 74 corrects changes in the light source over time and changes due to temperature. The above is called an image signal preprocessing circuit 70, and the image signal is converted into a digital value by an AD converter 76.

FIG. 7 is an explanation for one channel, or in the case of a three-line color sensor, it may be expanded to three channels. However, as described above, the output from the three-line color sensor requires correction of the R, G, and B CCD output levels. FIG. 7 shows an example in which this correction is performed by an inverting amplifier circuit 71, and the feedback gain is changed by changing the resistor 75 of the inverting amplifier circuit 71. Here, if the gain of the inverting amplifier circuit is set to 1 for the green CCD output, which has the maximum sensitivity to daylight fluorescent lamps, the gain of the inverting amplifier circuit for the blue and red channels is Gb = Sg ÷ Sb (4)
Blue Gr=Sg÷Sr (5)
It turns red.

0010

On the other hand, there is a demand for converting the image signal preprocessing circuit into an analog one-chip IC in order to reduce costs.

A conventional image signal preprocessing circuit 7 shown in FIG.
If you try to convert the 0 part into an analog one-chip IC,
The external resistor 75 becomes an obstacle and the circuit cannot be shared. The reason for this is that the internal arrangement and structure of the IC are restricted because the IC has elements outside. Further, depending on the material of the external resistor or the routing of the wiring pattern, the characteristics cannot be guaranteed, especially in the case of high-speed operation.

[0012] The present invention aims at commonizing the circuit while
The purpose is to correct the CCD output level due to the difference in sensitivity between G and B.

[0013]

[Means for Solving the Problems] The present invention provides a charge transfer channel having a plurality of charge transfer channels, each of which reads a color-separated original image and outputs an analog image signal for each pixel.
a CD image sensor (9) and a plurality of first emitter followers, each of which receives the output of each of the charge transfer channels with a transistor and outputs it with low impedance.
image reading means (30, 50) including (12, 13, 14)
, image processing means (40B, 40G,
40R) and image processing means (40B, 40G, 40
In an image reading device equipped with an A/D conversion means (45B, 45G, 45R) that converts an analog image signal outputted by the image reading means (30, 5R) into a digital image signal, the image reading means (30, 5
0) each have a plurality of first emitter followers (1
a plurality of correction means (18 to 20, Rba to Rbe,
Rga to Rge, Rra to Rre).

Note that symbols in parentheses indicate corresponding elements or matters in the embodiments shown in the drawings and described later.

[0015]

According to the invention of the present application, the image reading means (30, 50) includes a CCD image sensor (9) having a plurality of charge transfer channels and a plurality of first emitter followers (12, 13, 14). Correction means (18-20, Rba-Rbe, Rga-Rge
, Rra to Rre), there is no need to perform correction by externally attaching a resistor to the image processing means (40B, 40G, 40R) and changing the amplifier gain as in the conventional case.

[0016] Therefore, when the subsequent circuits, that is, the image processing means (40B, 40G, 40R) are made into an analog one-chip IC, for example, each channel can be shared. This reduces costs. In addition, even if an analog one-chip IC is not used, the circuit can be shared.

Other objects and features of the invention will become apparent from the following description of embodiments with reference to the drawings.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic configuration of an image reading apparatus 100 according to an embodiment of the present invention. In the case of a color scanner, basically a CCD has three charge transfer channels corresponding to three colors: R (red), G (green), and B (blue).
An image sensor 9 is provided. A contact glass 1 on which a read original is placed is illuminated by light sources 2a and 2b, and the reflected light from the image surface of the read original is reflected by a mirror 3.
, 4, 5, 6, 7 and lens 8.
The images are respectively formed on the light receiving surface of the sensor 9. Further, the light sources 2a, 2b and the mirror 3 are connected to a traveling body 10 that moves in the sub-scanning direction (horizontal direction in FIG. 1) parallel to the contact glass 1.
The mirrors 4 and 5 are mounted on a traveling body 11 that moves in the sub-scanning direction at 1/2 speed in conjunction with the traveling body 10, and by moving the optical system, the image plane of the read document is is scanned in the sub-scanning direction. Scanning in the main scanning direction (from the front to the back of the paper in FIG. 1) is performed by solid-state scanning of the CCD image sensor 9. In this way, the original image is read one-dimensionally by the CCD image sensor 9, and the entire surface of the original is scanned by moving the optical system.

FIG. 2 shows an outline of the configuration of the electric circuit of the image reading device 100. Note that the same parts as those in the circuit shown in FIG. 6 are denoted by the same reference numerals. CCD image sensor unit 3
In the circuit No. 0, one blue channel will be explained. 12 is a transistor circuit having resistors Rba and Rbb as emitter resistors, and constitutes a first emitter follower. Resistors Rba and Rbb constitute a voltage dividing circuit, the divided voltage becomes an input to the second emitter follower, and the output is outputted at low impedance through the DC cut capacitor 15. Note that the same operation applies to the green channel and the red channel. The purpose of this circuit is to correct and output the difference in the CCD output levels of R, G, and B, so the voltage division ratio of each color is determined so that the CCD image sensor unit output becomes Vob = Vog = Vor. . Now, the sensitivity of the CCD 3 line image sensor to daylight fluorescent light is Sb (blue), Sg (green), S
If r (red), illuminance on the CCD surface is Lc (1x), and accumulation time is t (sec), the output (V) from the CCD image sensor is Vb = Sb x Lc x t (6)
Blue Vg=Sg×Lc×t
(7) Green Vr=Sr×Lc×t
(8) It becomes red. The output (V) from the CCD image sensor unit 30 is divided by the first emitter follower and becomes as follows.

Vob=Vb×Rbb÷(Rba+Rbb)
(9) Blue Vog=
Vg×Rgb÷(Rga+Rgb)
(10) Green Vor=Vr×Rrb÷
(Rra+Rrb) (11)
RedHere, if we decide to output the blue CCD output with the lowest sensitivity at a division ratio of 1/1, Rbb÷(Rba+Rbb)=1
(12) Blue Rgb÷(Rga+R
gb)=Sb÷Sg (13) Green R
rb÷(Rra+Rrb)=Sb÷Sr (14)
Just decide the partial pressure ratio as shown in red. In this way, the output from the CCD image sensor unit 30 is corrected for the difference in sensitivity between R, G, and B and is output at the same voltage level, and the image signal preprocessing circuits 40B and 40G respectively
, 40R, the AD converter 45B,
45G and 45R are converted into digital data.

Image signal preprocessing circuits 40B, 40G, 40
The processing content in R is almost the same as the processing by the circuit shown in FIG.
Since the 0R inverting amplifier circuit 41 does not have an external resistor 75 as shown in FIG. 7, the image signal preprocessing circuit 40B
, 40G, and 40R can be easily integrated into an analog one-chip IC.

FIG. 3 shows an outline of the configuration of an electric circuit of an image reading apparatus 100 according to another embodiment. This circuit consists of the CCD image sensor unit 3 of the electric circuit shown in FIG.
0 is replaced with a CCD image sensor unit 50. One blue channel in the CCD image sensor unit 50 will be explained. 12 is a transistor amplifier in which Rbe is a collector resistance, and Rbc and Rbd are emitter resistances. The resistor Rbd determines the DC offset level, and the resistor Rbc determines the AC gain. Now, if the parallel resistance value of Rbd and Rbc is Rbf, the gain of the amplifier by the first transistor is Gb=Rb
e÷Rbf (15) Blue, however, Rbf=Rbc×Rbd÷(Rbc+Rbd)
It is expressed as 18 constitutes an emitter follower circuit which receives the inverted output of the first transistor as an input. The output of the emitter follower circuit 18 is the DC cut capacitor 1
5 and is output at low impedance. The same applies to the green and red channels. In this circuit as well, the resistance value of the inverting amplifier of the first transistor is determined to correct the difference in the R, G, and B CCD output levels. The output from the CCD image sensor is expressed by equations (6), (7), and (8) as in the case of FIG. Also, the gain by the transistor amplifiers 13 and 14 is as in the case of blue, Gg=Rge÷Rgf (16)
Green However, Rgf=Rgc×Rgd÷(Rgc
+Rgd)Gr=Rre÷Rrf (1
7) Red However, Rrf=Rrc×Rrd
It is expressed as ÷(Rrc+Rrd). That is, the output (V) from the CCD image sensor unit 50 is amplified by the first transistor amplifier and becomes as follows.

Vob=Vb×Rbe÷Rbf
(18) Blue Vog=Vg×Rge÷
Rgf (19) Green
Vor=Vr×Rre÷Rrf (
20) Red Here, if we output the green CCD output with the highest sensitivity with a gain of 1, Rbe÷Rbf=Sg÷Sb (21) Blue Rga÷Rgb=1 (22)
Green Rra÷Rrb=Sg÷Sr (23)
Just decide the resistance value and set the gain as shown in red. In this way, the output from the CCD image sensor unit is output at the same voltage level with the sensitivity difference between R, G, and B corrected. Thereafter, the image signals are processed by image signal preprocessing circuits 40B, 40G, and 40R similar to those shown in FIG. 2, and then converted into digital data by AD converters 45B, 45G, and 45R.

[0024]

As described above, according to the present invention, the image reading means (30, 50) includes the correction means (18 to 50) for correcting the unevenness of the output signal level due to the sensitivity difference between the respective charge transfer channels. 20, Rba~Rbe, Rga~
Rge, Rra to Rre), the subsequent circuits, that is, image processing means (40B, 40G, 40R)
For example, if it is made into an analog one-chip IC, each channel can be shared. This reduces costs. In addition, even if an analog one-chip IC is not used, the circuit can be shared.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an outline of the configuration of an embodiment of the present invention.

2 is a block diagram showing an outline of the configuration of an electric circuit of the image reading device 100 shown in FIG. 1. FIG.

3 is a block diagram schematically showing another electrical circuit configuration of the image reading device 100 shown in FIG. 1. FIG.

FIG. 4 is a graph showing the spectral sensitivity characteristics of a CCD.

FIG. 5 is a graph showing spectral distribution characteristics of a fluorescent lamp.

FIG. 6 is a block diagram showing an outline of the configuration of a conventional CCD image sensor unit 60.

FIG. 7 is a block diagram showing an outline of the configuration of a conventional image signal preprocessing circuit 70.

[Explanation of symbols]

1: Contact glass 2a, 2b
: Light source 3, 4, 5, 6, 7: Mirror
8: Imaging lens 9: CCD image sensor (CCD image sensor) 1
0, 11: Running body 12, 13, 14: Transistor circuit (first emitter follower) 15, 16, 17: DC cut capacitor 18, 19,
20: Emitter follower circuit (correction means) 30, 50:
CCD image sensor unit (image reading means) 40B, 40G, 40R: Image signal pre-processing circuit (image processing means) 45B, 45G, 45R: AD converter (A/D conversion means) 100: Image reading device Rba to Rbe, Rga ~Rge, Rra~Rre: Resistance (correction means)

Claims (3)

[Claims] 1. A CCD image sensor having a plurality of charge transfer channels, each of which reads a color-separated original image and outputs an analog image signal for each pixel, and each of which has a transistor that receives the output of each of the charge transfer channels. An image reading means including a plurality of first emitter followers outputting at low impedance; an image processing means for performing image processing on an analog image signal outputted by the image reading means; and an analog image signal outputted by the image processing means. In the image reading device, the image reading means includes a charge transfer channel, each of which is connected to a plurality of first emitter followers and corrects the output signal level thereof. An image reading device further comprising a plurality of correction means for correcting sensitivity differences between the images. 2. The correction means includes a voltage dividing circuit that divides the output of the first emitter follower using a resistor corresponding to a sensitivity difference between the charge transfer channels; 2. The image reading device according to claim 1, comprising: a second emitter follower that outputs an output. 3. The correction means includes an amplifier circuit that amplifies the output of the first emitter follower with an amplification factor corresponding to a sensitivity difference between the charge transfer channels; and a low impedance circuit that receives the amplified output. The image reading device according to claim 1, further comprising: a second emitter follower that outputs an output.