JPH0267873A - Picture reader - Google Patents

Abstract

PURPOSE:To facilitate picture processing including color separation by switching the reference voltage of an A/D converter for each color when the analog picture signal of plural colors obtained by color-separation-reading an original picture is A/D-converted. CONSTITUTION:When the analog picture signal of a CCD color image sensor 1 is A/D-converted, the reference voltage of an A/D converter 3 inputted from a reference generating circuit 4 is set for the signal levels of R, G and B respectively, and each time the picture signal is inputted, the reference voltage corresponding to the picture elements of R, G and B is switched. Consequently, all of 3-color digital data corresponding to R, G and B filters respectively outputted from the A/D converter 3 can be handled as a gradation signal whose 32 gradations are equal. Thus, the picture processing including the color separation can be executed with a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device that separates and reads a document by color.

[Conventional technology]

Recently, personal computers, word processors, etc. are equipped with handheld black and white image reading devices for inputting images, but along with the development of inks such as Y, M, and C, color image processing has become possible. This has led to the development of reading devices that convert color images into electrical signals and input them into personal computers, word processors, and the like.

As an image sensor for reading color images, it has a plurality of light receiving elements arranged in a line, and has R in the line direction.
Continuous RGB with GB stripe filter
A CCD color image sensor, etc., which performs color separation of areas corresponding to a document on a document, is known.

Then, by converting the analog color signals from the light-receiving elements corresponding to the R, G, and B filters into digital color signals, and performing color calculations between these digital color signals, a color image signal for full-color image reproduction is generated. is formed.

[Problem that the invention is trying to solve] However,
Generally, R read out from a CCD color image sensor,
The dynamic ranges of G and B signals are not equal. Therefore, in an image reading device that amplifies analog color signals of three colors, performs A/D conversion on the amplified signals, and digitally processes image data, the white of each R, G, and B image is Black from the level! Each novel has a different number of gradations.

This is because the spectral distribution of the illumination light source in the visible region is not uniform, and the light transmittance and C of the R, G, and B filters attached to the CCD color image sensor are also different.
This is due to the fact that CDs have different sensitivities to wavelength ranges.

An example of the spectral distribution of the illumination light source is shown in Figure 6, and R, G
FIG. 7 shows an example of the sensitivity for the wavelength range of 8 pixels.

When a white document is illuminated with a light source having the spectral distribution shown in FIG. 6, the signal levels of R, G, and B are the highest for R, followed by G and H, respectively.

At this time, if the reference voltage of the A/D converter with 5-bit resolution is set to match 2 pixels, 2 pixels will have 32 gray levels, but 6 pixels will have 26 gray levels.

8 pixels have only 20 gradations.

If the number of gradations from the white level to the black level of each R, G, and B pixel differs in this way, it becomes difficult to perform color separation of the document, and thus to perform image processing.

In order to solve this problem, as shown in Figure 8, the CCD
Analog signal amplification units 21 to 23 that input pixel signals of I
are provided, and the respective gains are adjusted to each RGB pixel.

Then, I thought of a method of synchronizing the outputs of the three amplifying sections 21 to 23 with the driving timing of the CCD 1, sequentially selecting them with the selector 24, and sending them to the A/D converter 3, thereby obtaining 32 gray levels for all three pixels. However, the disadvantage is that the circuit scale becomes large.

[Means for solving problems]

The present invention has been made in view of the above points, and makes it possible to perform good color image processing by making the number of gradations of multiple colors approximately equal after digital conversion. reading means for reading and outputting analog image signals of multiple colors; converting means for converting the analog image signals of multiple colors into digital image signals of multiple colors; The present invention provides an image reading device having a control means for switching to.

〔Example〕

FIG. 3 is an electrical block diagram of a color image reading device to which the present invention is applied. 1 is a COD color image sensor with an RGB stripe filter that reads color images.

2 is an amplifier that amplifies the analog image signal of the CCD color image sensor l, and 3 is an A/D that converts the analog image signal amplified by the amplifier 2 into a digital image signal.
The converter is, for example, HA19216 manufactured by Hitachi. 4 is a reference generation circuit that generates a reference voltage for the A/D converter 3;

FIG. 4 shows the configuration of the CCD 1, in which each pixel of a plurality of light receiving elements arranged in the main scanning direction includes an R filter 41°G filter 42. B filters 43 are sequentially and repeatedly applied.

The signal read by the CCD sensor 1 is a serial signal containing a mixture of a plurality of color signals such as R, G, B, R, G, B corresponding to the array of filters. and,
Three consecutive RGB pixels are treated as one set, and YMC data corresponding to an area of three pixels is generated.

Next, the operation of the embodiment will be explained.

A color image illuminated by a white illumination light source is photoelectrically read by a CCD sensor 1, and each color signal R, G, B transmitted through each RGB filter is sequentially output in the main scanning direction, and after being amplified by an amplifier 2. The signal is input to an A/D converter 3 having a resolution of 5 bits. The A/D converter 3 receives two reference voltages VT from the reference generation circuit 4.
and enter VU. That is, when the input signal voltage from the amplifier 2 is VT, the A/D converter 3 outputs 31 (11111), and when the input signal voltage is VU, it outputs O(0000
0) is output. That is, V u = VT (The input voltage between 0 is subdivided in (VT-VB)/31 steps to express 31 gray levels.

Incidentally, the gain of the amplifier 2 is set so that the output voltage of the six pixels becomes Vg when a white original is read. At this time, two pixels from amplifier 2 when reading a white original with this gain.

The output voltages of the eight pixels are Vr and Vb, respectively. The magnitude relationship is Vr>Vg>Vb.

Also, the output voltages when reading a black original are R and G.

B both output voltage Vr.

Reference voltages VU and V input to A/D converter 3
The configuration of the reference generation circuit 9 that generates T is shown in FIG.

11 to 13 are analog switches, such as Toshiba's TC4566F, and control signals R8W, GSW
.

The opening and closing of the switch is controlled by the BSW. Control signal R3 that controls opening and closing of analog switches 11 to 13
The timing pulses of W, GSW, and BSW are as shown in FIG.

The resistance values of the resistors R and ~R7 are set so that the potentials at points X, Y, a, b, and c are Vx, Vy, Vr, Vg, and Vb, respectively, and here, Vx=Vr, Vy=V
It is u.

That is, when A/D converting the signals of two pixels, the analog switch 11 is closed by the control signal R3W,
A voltage Vr is input to the VT input terminal of the A/D converter 3. Similarly, when the signals of 6 pixels are A/D converted, the analog switch 12 is closed by the control signal GSW, and the voltage Vg is closed, and when the signal of 3 pixels is A/D converted, the analog switch 13 is closed by the control signal BSW.
is closed and voltage vb is input to each vT input terminal.

The control signals R3W, GSW, and BSW are shown in Fig. 5 (a).
) is realized by the circuit. 51 is, for example, TI's 74L
This is a 4-bit counter such as 3163. 52 is TI company 7
4L5138 or the like is a 3:8 decoder, and 53 is an inverter such as TI's 74LS04.

The 4-bit counter 751 receives R and G signals from the amplifier 3.

A clock CL K 1 synchronized with each pixel of the B signal is input, and the output terminals QA, Qa, and Qc are respectively connected to the decoder 5.
It is input to the A, B, and C terminals of 2. At this time, output Qo is open. The output of the decoder 52 is γ.

The logic of ``71'' is inverted by the inverter 53.

At this time, outputs 7 to 7 are open. Furthermore, output ■ is input to the LOAD terminal of counter l, and CLK
The load value 0000 is loaded in synchronization with 1.

As shown in FIG. 5(b), the outputs of the inverter 53, R3W, GSW, and BSW, are RlG from the amplifier 3,
The signals are output in correspondence with the B signals.

By performing such control, 3 signals corresponding to each of the R, G, and B filters output from the A/D converter 3 are
All color digital data can be handled as gradation signals of 32 gradations.

This gradation signal is input to, for example, an image processing circuit (not shown), undergoes processing such as complementary color conversion and masking, and is output as Y, M, and C print data to the outside of the apparatus.

As explained above, when A/D converting the analog image signal of the CCD color image sensor, the reference voltage of the A/D converter is set to match the R, G, and B signal levels, and the pixel signal is R, G every time input
, B, all pixel levels can be expressed in 32 gradations by switching the reference voltages corresponding to the pixels.

Note that the setting range of the reference voltage input terminal of the A/D converter is generally allowed to be approximately ±50% of the input dynamic range VT-vu for the recommended setting voltage value.
If the reference voltage is configured to be switched within this range, the conversion accuracy of the A/D converter will not fluctuate.

〔Effect of the invention〕

As explained above, according to the present invention, when A/D converting a plurality of color analog image signals obtained by color-separated decoding of a document image, color Image processing including decomposition can be performed well.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the reference generation circuit, Figure 2 is a diagram showing reference voltage switching, Figure 3 is an electrical block diagram of a color image reading device, and Figure 4 is a diagram showing the configuration of a CCD color image sensor. , FIG. 5(-k) is a blower diagram of the control signal generation circuit, FIG. 5(S) is a timing chart diagram showing the generation of the control signal,
Figure 6 is a diagram showing the spectral distribution of a white illumination light source;
The figure shows the sensitivity to the wavelength range of each RGB pixel of CCD1, and Figure 8 is a block diagram of the correction circuit, where 1 is a color image sensor, 2 is an amplifier, 3 is an A/D converter, and 4 is a reference generator. The circuit includes analog switches 11 to 13, and a selector 24.

Claims (1)

[Claims] a reading means for color-separating a document image and outputting a multi-color analog image signal; a converting means for converting the multi-color analog image signal into a multi-color digital image signal;
An image reading apparatus comprising: a control means for switching the reference voltage of the converter each time each color signal is input.