JPS63224475A - Color image reader - Google Patents

Abstract

PURPOSE:To receive a color image with good color reproducibility by providing a white reference plate adjacently to an original, reading the white reference plate by a line image sensor every time one line of an original is read, and performing AGC based upon the output. CONSTITUTION:Images of the original 14 and white reference plate 15 which are lighted by a light source 12 are formed on the line image sensor 11 through a rod lens array 13. An image signal outputted by the line image lens array 13 is amplified by an amplifier 21 and inputted to an AD converter 22. Further, the image signal of the white reference plate is supplied to a sample holding circuit 23 to sample and hold only the image signal of a W element, and the resulting signal is inputted as a reference voltage to an AD converter. The reference voltage ref inputted to the A/D converter is generated by amplifying the output of the sample holding circuit by an amplifier 24 with a proper amplification factor so that an image of one line is within the A/D conversion range. Consequently, even if the quantity of light from the light source varies in the middle of subscanning, the reference voltage ref inputted to the A/D converter varies at an equal rate.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention... The present invention relates to an automatic gain graphic circuit (AGC circuit) I of an image reading device that reads color images.

[Conventional technology]

FIG. 3 is a perspective view showing a conventional general image reader. In the figure, Uυ is a line image sensor. α is a light source, 113 is a rod lens array, and ■ is a manuscript. The image of document A4 illuminated by light source [IX5 is
It enters the line image sensor αD from the rod lens array Q311.

Sub-scanning normally takes several seconds, but if the light source α3 changes during that time. The output signal of the line image sensor Qυ changes. Uniform color images cannot be obtained. For this reason, conventional image readers are provided with an AGC circuit.

FIG. 4 shows a conventional AGC circuit disclosed in, for example, Japanese Unexamined Patent Publication No. 169273/1982. In the figure, I is a differential amplifier, 0 is an amplifier, 13 is a black voltage peak detection circuit, 1
441 is a Hakudeno peak detection circuit, and 441 is a variable resistor.

Next, the operation will be explained. The image signal X thus read by the line image sensor a in FIG. 3 is input to the non-inverting input terminal of the differential amplifier 3I+tl in FIG. The black voltage peak detection circuit o3 compares the black part peak value of the image signal y amplified by the amplification 9o and the first reference voltage Vref' for each reading line, and holds the difference. This difference is input to the inverting input terminal of the differential amplifier UU. As a result, the differential amplifier t4D subtracts the first difference signal from the one image signal X, and the peak of the black voltage of the amplifier A3 becomes equal to the first reference voltage Vref l.

On the other hand, the peak value of the white voltage is manually input to the amplification factor adjustment circuit +441, and the 1vl1 width factor adjustment circuit I compares the peak value of the white voltage with the second reference voltage Vref 2 and outputs the difference voltage. . Then, the value of the variable resistor (c) is adjusted using the differential voltage so that the white voltage peak value for each line of the image signal y becomes equal to the second reference voltage Vref2.

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

[Problem to be Solved by the Invention 3 The above AGC circuit detects and stores the density range in the document and performs AGC, so it is difficult to adjust the AGC for color documents with few white and black areas. be. Furthermore, there is a problem in that color reproducibility deteriorates for color IJλ documents that have no white or black portions.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a color image reader that can easily perform AGC regardless of the type of document and has good one-color reproducibility.

[Means for solving problems]

In the AGC circuit according to the present invention, a white reference plate is provided next to one document, the white reference plate is read by a line image sensor every time before reading one line of the document, and AGC is performed using the output as a reference. This is what I did.

[For production]

In the present invention, by using a white reference plate as a reference for the white level, AGC can be easily performed in response to changes in light from a light source even on an original with few white areas.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In Figure 1, αυ is a line image sensor.

The eel is a light source, (13 is a rod lens array, (141
is the manuscript.

αS is a white reference plate. Here, the line image sensor aυ used has a length that allows it to simultaneously read both the document α and the white reference plate a9.

Figure 2 shows an example of the AGC circuit, where συ is a line image sensor, and c! υ is 4 width 3a, cn is A/D conversion 3
．． c! 3 is a sample hold circuit that holds the white reference voltage, and c24 is an amplification 3t+.

In addition, the line image sensor has one pixel that is white (Wl).
, red (R), green (G), and blue (B).

Next, the operation of this embodiment will be explained.

In Figure $1, an image of the original I and the white reference plate α9 illuminated by the light source a2 is formed on the line image sensor αυ by the rod lens array Q3.

In FIG. 2, both signals output from the line image sensor are amplified by an amplifier 15aQ, and then input to an AD converter 4. Also, the image signal of the white reference plate is as follows.

The sample bold circuit @ samples and holds only the image signal of the W element, and inputs it as a reference voltage to the AD converter.

FIG. 5 shows signal waveforms at major locations in FIG. 2. In Fig. 5fa), S is the image signal manually input to the A/D converter, and in Fig. 5+1)), S/H is W of the white reference plate.
Pulse 5th to sample and hold only the image signal of the element
In the diagram (C), ref indicates a reference voltage to the A/D converter. Further, as shown in FIG. 5C, the image signal S has a lower level near both ends of one line than in the center of one line due to the shading effect of the light source. Therefore the second
As shown in the figure, the reference type EE re is manually input to the A/D converter.
f amplifies the output of the sample and hold circuit by an appropriate magnification by amplifier B4 so that one line of image signal falls within the A/D conversion range.

From the above configuration, even if the light base of the light source changes during sub-scanning and the image signal changes from S to S' as shown in FIG. 6 [a) (1)), the A/D The reference voltage ref applied to the converter changes at a rate equal to the image signal. That is, ref' = reL (S'/S). Therefore, a uniform output from the A/D converter can be obtained regardless of changes in the amount of light.

Note that in the above embodiment, W is used as the line image sensor.
, R, G, and B, but other element configurations 9 such as W, Y (yellow), and C (
An image sensor having complementary color elements of 1M (cyan) and 1M (magenta) may be used.

In addition, in the above embodiment, the white reference plate was placed on the right side of the document as shown in Figure 1, but the change in light distribution of the light source was sufficiently slower than the one line reading time of the line image sensor. If so, the white reference plate may be placed on the left side of the document.

〔Effect of the invention〕

As described above, according to the present invention, stable AGC can be easily performed regardless of the type of document.

You can receive color images with good color reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a color image reader according to an embodiment of the present invention, FIG. 2 is a diagram showing an AGC circuit according to the same embodiment, FIG. 3 is a perspective view of a conventional image reader, and FIG. 4 is a perspective view of a conventional image reader. Diagram showing the AGC circuit, Figure 5 (all)) [C]
6 is a signal waveform diagram of each part of an AGC circuit according to an embodiment of the present invention, and FIG. 6(a) (1)) is a diagram for explaining the relationship between a change in an image signal and a change in a reference voltage. αυ is a line image sensor, α4 is an original, α9 is a white reference plate, 4 is an A/D converter, ﾆ is a sample and hold circuit, and @ is a term ranger. In addition, in FIG. 1, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A white reference plate placed adjacent to the original, a line image sensor having a width that can read the white reference plate and the original at the same time, and the line image sensor holding the output from reading the white reference plate. A color image reading device comprising: a sample and hold circuit for converting the output of the line image sensor; and an A/D converter for converting the output of the line image sensor from analog to digital. (2) The output of the sample hold circuit is A (A≧1)
2. The color image reading device according to claim 1, wherein the reference voltage of the A/D converter is multiplied by the reference voltage of the A/D converter.