JPS63316567A - Color image reader - Google Patents

Abstract

PURPOSE:To attain easy gain control independently of the sort of an original by reading out also a white reference plate arranged adjacently to the original and controlling the A/D conversion of an original reading output in each line. CONSTITUTION:The white reference plate arranged adjacently to an original is read out by a line image sensor 11 together with the original, the output of a W and Ye element string is supplied to an A/D converter 23 through an amplifier 21 and the output of the W element is simultaneously held in a sample holding circuit 25. The held value is converted into a reference voltage through an amplifier 27 and the converter 23 is controlled to automatically adjust gain in a density range. Since the output of G and Cy elements are similarly processed, gain control can be easily executed in each line independently of the sorts of originals, a uniform color image can be obtained and color reproducing can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device for reading color images.

[Conventional technology]

FIG. 5 is a perspective view showing a conventional image reader. In the figure, 11 is a line image sensor, 12 is a light source,
13 is a rod lens array, and 14 is a document. In this image reader, a document 14 illuminated by a light source 12 is used.
The image enters the sea line image sensor 11 through the rod lens array 13.

Furthermore, sub-scanning usually takes about several seconds, but if the amount of light from the light source 12 changes during that time, the output signal of the line image sensor 11 changes, making it impossible to obtain a uniform color image.

Therefore, conventional image readers are provided with an automatic gain control circuit (hereinafter referred to as an AGC circuit).

FIG. 6 is a block connection diagram showing a conventional AGC circuit disclosed in, for example, Japanese Unexamined Patent Publication No. 60-169273. In the figure, 41 is a differential amplifier, 42 is an amplifier, and 43 is a pyrovoltage peak detection circuit. , 44 is a white voltage peak detection circuit, 4
5 is a variable resistor.

Next, the operation will be explained. The image signal X read by the line image sensor 11 shown in FIG. 5 is input to the non-inverting input terminal of the differential amplifier 41 shown in FIG. The pyrovoltage peak detection circuit 43 compares the black part peak value of the image signal y amplified by the amplifier 42 and the first reference voltage Vrefl for each reading line, and holds the difference. This difference is input to the inverting input terminal of the differential amplifier 41. As a result, the differential amplifier 41 subtracts the difference signal from the image signal X, and the peak of the pyroelectric voltage of the amplifier 42 becomes equal to the first reference voltage Vrefl.

On the other hand, the peak value of the white voltage in the image signal y is input to the amplification factor adjustment circuit 44, and the amplification factor adjustment circuit 44 serving as a white peak voltage detection circuit compares the peak value of the white voltage with the second reference voltage Vref2. and output the difference voltage. Then, with this differential voltage, the value of the variable resistor 45 is set so that the white voltage peak value for each line of the image signal y becomes the second reference voltage Vref2.
Adjust so that it is equal to

With the above configuration, the amplitude between black and white of the image signal y is corrected to be constant, and the background density of the original is removed.

[Problem that the invention seeks to solve]

Since the conventional color image reading device is configured as described above, it is necessary to detect and store the density range in the document 14 and perform gain control.

In addition to difficulty in controlling the gain as described above for color originals with few black areas, there are also problems such as poor color reproducibility for color originals with no white or black areas.

This invention was made to solve the above-mentioned problems, and it is possible to easily perform gain control regardless of the type of original, thereby making it possible to obtain a uniform color image. An object of the present invention is to obtain a color image reading device that can improve color reproducibility.

[Means for solving problems]

A color image reading device according to the present invention includes a white reference plate provided next to a document, and a line image sensor having a plurality of rows that reads this white reference plate every time one line of the document is read, and samples each output. The output of the line image sensor is held by a hold circuit, and the output of each column of the line image sensor is converted into digital data by an analog/digital converter using the held output as a reference voltage.

[For production]

The analog/digital converter of the present invention uses a white reference plate as a white level reference, and converts the obtained reference voltage to multiple image signals read by multiple rows of line image sensors at a rate equal to that of the image signals. This makes it possible to easily adjust the gain in response to changes in the amount of light from a light source even for originals with few white areas, thereby preventing deterioration of color reproducibility.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 11 is a line image sensor, 12 is a light source, 13 is a rod lens array, 14 is an original, and 15 is a nine-white reference plate arranged adjacent to the original 14. Here, the line image sensor 11 is connected to the original 14 and the white reference plate 15.
Use a length that allows both to be read at the same time.

FIG. 2 shows an automatic gain control circuit in the color image reading device of the present invention. In the figure, 11 is a line image sensor, 21 and 22 are amplifiers, and 23 and 24 are analog
Digital converter (hereinafter referred to as A/D converter), 25
．． 26 is a sample and hold circuit, and 27 and 28 are amplifiers.

The line image sensor 11 is composed of two rows of image sensors, each row consisting of white (W), yellow (Ye), green (G), and cyan (Cy) elements. The image signals are output in the above order. In this way, one pixel is made up of these four elements.

Next, the operation of this embodiment will be explained.

First, in FIG. 1, an image of an original 14 and a white reference plate 15 illuminated by a light source 12 is an image of a rod lens array 1
3, the image is formed on the silhouette image sensor 11. In FIG. 2, the image signal output from the line image sensor 11 is sent to an amplifier 21 in a column having W and Ye elements.
Further, the columns having G and Cy elements enter the amplifier 22 and are amplified, respectively.

Output 5(1) of amplifier 21 is input to A/D converter 23. Further, as for the image signal of the white reference plate, only the image signal of the W element is sampled and held by the sample and hold circuit 25, and this is used as a reference voltage of the A/D converter 23.

Furthermore, the signal flow of the output 5(2) of the amplifier 22 is similar to the signal flow of the image signal 5(1). However, 5(2
), the sample and hold circuit 26 samples and holds the image signal of the G element.

FIG. 3 shows signal waveforms at major locations in FIG. 2. In FIG. 3, Sα) is the image signal input to the A/Il converter 23, S/H is the pulse that samples and holds only the image signal of the W element of the white reference plate, and ref (1) is the A/D
Reference voltages to converter 23 are shown respectively.

Further, as shown in FIG. 3, the image signal 5(1) has a lower level near both ends than the center of one line due to the shading effect of the light source 12. Therefore, as shown in FIG. 2, the reference voltage ref(1) input to the A/D converter 23 is set by multiplying the output of the sample and hold circuit 25 by an appropriate multiplying factor (for example, Ai times (Ai>1)) by the amplifier 27. ) so that the image signal for one line falls within the A/D conversion range.

Even if the number changes from 5(1) to S'(1), A
The reference voltage ref(1) input to the /D converter 23 changes at the same rate as the image signal. That is, ref'(1) = raf(1) ・(S'(1
)/5(1) ). Therefore, although the method of optical gain control for the output of the A/D converter 23 has been described, in the case of the output S (2) of the amplifier 22, the image signal of the 9G element is sampled and held by the sample and hold circuit 26. , the operation is exactly the same except that the reference voltage ref(2) of the A/D converter 24 is used.

In this way, reference signals ref(1)e ref(2) of separate systems are obtained from the image signal of the KXW element and the image signal of the G element.
), and based on these, 1) Since each of the AID converters 23 and 24 reads white, the white reference reading υ is more accurate than in the case of one system, and changes in the amount of light are Regardless, the outputs of the A/D converters 23 and 24 are uniform.

In the above embodiment, the line image sensor 11 has four elements W, Ye=G, C)', but other element configurations, for example W.

An image sensor having primary color elements of R (red), G (green), and B (blue) may be used.

Furthermore, in the above embodiment, the white reference plate 15 was placed on the right side of the original 14 as shown in FIG.
The change in the light amount of the light source 12 causes the line image sensor 11 to
If the line reading time is slow enough, the white reference plate 15
may be placed on the left side of the document 14.

Further, in the above embodiment, a case has been described in which the line image sensor 11 having a two-row configuration is used. Sample hold output ref (i) (
The reference voltage of the first A/D converter may be obtained by multiplying Ai (Ai≧1) by Ai (Ai≧1), where i is an integer and l≦1≦N, and the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, a white reference plate is provided next to a document, and a plurality of lines of line image sensors are used to read the white reference plate in multiple systems for each line of the document. Since the gain is adjusted based on the output of the light source, it is possible to perform gain control with high precision regardless of the type of document, even when the document has few white areas, and even when the light intensity of the light source changes. The effect is that a color image with good color development property can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of a color image reading device according to an embodiment of the present invention, FIG. 2 is a block connection diagram showing an automatic gain control circuit of the power 2-image reading device, and FIGS. FIG. 2 is a signal waveform diagram of each part of the circuit to explain the operation of the automatic gain control circuit, FIG. 5 is a schematic perspective view of a conventional color image reading device, and FIG. 6 is a circuit diagram showing the conventional automatic gain control circuit. It is. 11 is a line image sensor, 14 [iil, 15 is a white reference plate, 23.24 is an analog/digital converter,
25.26 is a sample hold circuit.

Claims (2)

[Claims] (1) A white reference plate placed adjacent to the document, a line image sensor having a plurality of rows having a width that allows simultaneous reading of the white reference plate and the document, and each row of the line image sensor connected to the white reference plate. A color image reading device comprising a plurality of sample and hold circuits that hold outputs obtained by reading a board, and a plurality of analog/digital converters that digitally convert the outputs of each column of the line image sensor. (2) The output of the i-th (i is an integer, 1≦i≦N) sample and hold circuit is multiplied by Ai (Ai≧1) and used as the reference voltage of the i-th analog/digital converter. A color image reading device according to claim 1.