JPS62230263A - Picture signal processing circuit - Google Patents

Abstract

PURPOSE:To obtain a binary-coding signal where the variation of the sensitivity of a photoelectric transducing cell and the lighting of an original are corrected by generating a threshold data from the combination between a dark reference data and a light reference data so as to store the result in a RAM. CONSTITUTION:A dark original with less glitter is read from an image sensor at first and given to the 1st address input of a ROM 4 via an A/D converter 2 and a latch circuit 3. The data are writen in a RAM 5. Then white paper with high reflectance is read by the image sensor and given to the 1st address input A1 of the ROM 4 similarly as the light reference data. The dark reference data stored in the RAM 5 is given to the 2nd address input A2 of the ROM 4, resulting that the threshold data corresponding to the combination of the dark reference data and the light reference data is outputted from the ROM 4 and written in the RAM 5. The picture data read are subjected to binary coding processing based on the said threshold data.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a circuit that processes image signals output from an image sensor, and particularly relates to a circuit that processes image signals output from an image sensor, and in particular, to prevent variations in the sensitivity of photoelectric conversion cells in the image sensor. The present invention relates to an image signal processing circuit that compensates for variations in illumination.

(Prior art i) The image sensor used to read images on documents in facsimile machines, copying machines, etc. is a CCD.

It is constructed by arranging a large number of photoelectric conversion cells made of CdS, amorphous silicon, or the like. In such an image sensor, variations in sensitivity and variations in illumination among photoelectric conversion cells corresponding to pixels pose problems.

Japanese Unexamined Patent Application Publication No. 12175/1988 discloses an image sensor output correction circuit for compensating for such variations. This correction circuit consists of a memory circuit that stores the dark signal, a subtraction circuit that subtracts the dark signal from the bright signal to generate a sensitivity component, a subtraction circuit that subtracts the dark signal from the image signal to generate a signal component, and a sensitivity component. a memory circuit that stores -
and a division circuit that divides the signal component by the sensitivity component to obtain a normalized image signal. Further, normally, the normalized image signal is further converted into 2111I by a comparator and output.

Here, each of the two sets of memory circuits requires a capacity for one line of digital image signals, and arithmetic circuit parts such as subtraction and division circuits, especially division circuits, generally require a large number of circuit elements. do. Therefore, this correction circuit has a considerably large circuit scale.

(Problems to be Solved by the Invention) As described above, the conventional correction circuit has a problem in that the configuration is complicated and the cost is high.

An object of the present invention is to provide an image signal processing circuit that can obtain a binary image signal in which the effects of variations in sensitivity of photoelectric conversion cells and variations in illumination are corrected, using a simple configuration with a small number of parts. purpose.

- [Structure of the Invention] (Means for Solving the Problems) The present invention provides a first memory whose first address input is the output of an A/D converter that converts an analog image signal from an image sensor into a digital signal. a second storage circuit for storing data applied to a second address input of the first storage circuit, the data being applied from the A/D converter and the second storage circuit in the first storage circuit Threshold data based on the bright reference data and dark reference data and a binarized image signal based on the threshold data are output, and the second storage circuit outputs threshold data based on the bright reference data and the dark reference data. A feature is that threshold data is stored. That is, the arithmetic circuit portion is configured by a first memory circuit <ROM), and the second memory circuit is shared for storing dark reference data or bright reference data and storing threshold data for binarization. It is something.

(Function) In the present invention, before reading an image with the image 4 sensor, dark reference data and bright reference data are created sequentially via the image sensor and the A10 converter. First, the reference data obtained first is written into the second storage circuit via the first storage circuit. Next, threshold data corresponding to the combination of the later obtained reference data of the dark reference data and the bright reference data and the reference data stored in the second memory circuit is sequentially outputted from the first memory circuit; The contents of the second storage circuit are changed according to this threshold value data. , when actually reading an image, the image signal data inputted through the A/D converter and read from the second storage circuit,
A binarized image signal corresponding to the comparison result with the output threshold data is read out from the first storage circuit.

(Embodiment) FIG. 1 is a block diagram showing the configuration of an image signal processing circuit according to an embodiment of the present invention. An analog image signal from an image sensor is input to the input terminal 1, and is converted into a digital signal with an appropriate number of bits by the A/D converter 2.
It will be done.

The output of the A-/D converter 2 is passed through the latch circuit 3 to the first
The first address A1 of ROM4 as a storage circuit of
given to ru. ROjVI4 2nd address human power A
2, the outputs of R, A, M, .

The RAM 5 individually stores dark reference, dark reference data, and threshold data for binarizing image signals at addresses corresponding to each photoelectric conversion cell (pixel) in the image sensor. It is for.

The data read from the RAM 5 is temporarily held in a latch circuit 6, and then transferred to the A/D converter 2 held in the latch circuit 3.
The data is input to the ROM 4 in synchronization with the output data of.

The ROM 4 is used to create threshold data corresponding to the combination of the dark reference data and the bright reference data, and to create a binary image signal that is the comparison result between the threshold data and the image signal data read out from the R''AM 5. The pre-calculated data is held at the address corresponding to the combination of input data of address inputs A1 and A2.The binary image signal outputted from the ROM 4 is outputted via the latch circuit 7. Sent to terminal 8.

Next, the operation of this image signal processing circuit will be explained.

First, prior to reading an image, a black document with low gloss is read by an image sensor, and the signal output from the image sensor at that time is taken out as dark reference data via the A/D converter 2 and sent to the latch circuit 3. via ROM4
The first address of A1 is given to A1. The second address A2 of the ROM4 is connected to the RA via the latch circuit 6.
All rOJ data is given from M5. At this time, data that is the same as the dark reference data or data that corresponds to an appropriately processed version of the dark reference data is read out from the ROM 4.
Written to RAM5.

Next, the white paper with high light reflectance is read by the image sensor, and the signal output from the image sensor at that time is A/
It is taken out as bright reference data via the D converter 2, and is applied to the first address input A1 of the ROM 4 via the latch circuit 3 as before. At this time, the dark reference data stored in the RAM 5 is also read out at the same time and applied to the second address input A2 of the ROM 4 via the latch circuit 6.

As a result, threshold data corresponding to the combination of dark reference data and bright reference data is read from RC)M4. That is, for example, a value obtained by subtracting the dark reference data of the corresponding pixel from the bright reference data and multiplying it by an appropriate coefficient M between O and 1 is read out as threshold data, and this is read out as threshold data.
The dark reference data is written in place of the dark reference data. In the example of FIG. 2, a value obtained by multiplying the difference between the dark reference data and the bright reference data by M=O,'6 is written in the RAM 5 as the threshold value data. 'Figure 2 shows examples of dark reference data, bright reference data, and threshold data that are actually obtained. The horizontal axis corresponds to time, which corresponds to each photoelectric conversion cell, or pixel, of the image sensor, and the vertical axis corresponds to A. /D converter 2 output value is shown.

When threshold value data corresponding to all pixels, that is, all photoelectric conversion cells in the image sensor are written into the RAM 5 in this way, the actual image on the document is read by the image sensor. The analog image signal obtained by this is A
The digital image data is converted into digital image data by the /D converter 2 and is applied to the first address A1 of the ROM 4 via the latch circuit 3. At the same time, the threshold value data of the corresponding pixel is read from the RAM 5 and is transferred to the ROM 4 via the latch circuit 6. The second address of A2 is given to A2. At this time, ROM4
From address input A1. The comparison result of the data input to A2 is read out as 1-bit data, which is outputted to the output terminal 8 via the latch circuit 7 as a binary image signal. That is, if the image data is larger than the corresponding threshold data, "1" is output, and if it is smaller, data rOJ is output.

In addition, in the above configuration, even if some of the many photoelectric conversion sensors in the image sensor are defective, it is possible to easily take a repair position.For example, in the process of obtaining bright reference data. , if the signal level from a specific photoelectric conversion cell is extremely low even though a blank original is being read, the ROM 4 determines that cell to be defective and displays the information in Figure 2. RA'M as shown
5, the full scale value, that is, all "
1”. However, if the cell is determined to be normal, the i value data will be used and the t full scale value will not be used.

Then, during actual image reading, the image signal from the cell determined to be defective is transferred to the A/D converter 2 and the latch circuit 3.
Even if it enters the address A1 of ROM4 through RO
M4 ignores this.

In this case, the ROM 4 controls the latch circuit 7 to maintain the binary image signal corresponding to the image signal from the cell determined to be defective at the same value as the previously obtained binary image signal. Specifically, for example, as the latch circuit 7, J-
It is sufficient to use a flip-flop for , and control the input of the terminal to J.

The input/output logic of the flip 70 tube in J- is shown in the table below.

Therefore, when image data from a cell determined to be defective is input, the output from the ROM 4 to the latch circuit 7 LJ- (flip 70) is set to J=L.

If K-L, the binarized image signal is held at the value of Qn-1, that is, the same value as the binarized image signal obtained immediately before.

Generally speaking, considering the application of image reading devices in facsimiles and the like, when obtaining a binary image signal, the A/D converter 2 for digitizing an analog image signal has a quantization bit number of 4 to 6 bits. A certain degree is used. In that case, the output of RAM5 is assumed to be 6 bits, and RO
The number of address inputs for M4 is 12, which is less than that of a normal 1.6 or 64 memory. Therefore, the circuit of the present invention replaces the arithmetic circuit with one RO.
M, and can be realized with a simple configuration that does not require large-scale digital arithmetic circuits (subtraction circuits and division circuits) as in the past, which is very advantageous in terms of cost. If EPROM, mask ROM, etc. are used, further cost reduction can be achieved.

In addition, since the arithmetic circuit part is a memory, it is possible to change the threshold level for binarization or the data correction method for defective cells depending on the characteristics of the image sensor, the required specifications of the entire system, etc. This can be done more easily than when using random logic such as an ALU.

[Effects of the Invention] According to the present invention, with a simpler configuration than the conventional one mainly consisting of two memory circuits, it is possible to perform binarization that compensates for variations in sensitivity of photoelectric conversion cells, variations in illumination of originals, etc. An image signal can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an image signal processing circuit according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of the embodiment. DESCRIPTION OF SYMBOLS 1...Analog image signal input terminal, 2...A/D converter, 3...Latch circuit, 4...ROM (first memory circuit), 5...RAM (second memory) circuit), 6
...Latch circuit, 7...Latch circuit, 8...Binarized image signal output terminal.

Claims (2)

[Claims] (1) A/A/
A D converter, a first memory circuit whose first address input is the output of the A/D converter, and a second memory which stores data to be applied to the second address input of the first memory circuit. The first storage circuit stores threshold data based on bright reference data and dark reference data provided from the A/D converter and the second storage circuit, and generates binary data based on the threshold data. An image signal processing circuit that outputs a converted image signal, and the second storage circuit stores either the dark reference data or the bright reference data and the threshold value data. (2) The first storage circuit includes a latch circuit that temporarily stores the binary image signal output from the storage circuit when any of the bright reference data is below a predetermined level.
Claims characterized by having a function of performing control to maintain the binary image signal from the corresponding photoelectric conversion cell at the same value as the binary image signal obtained immediately before. The image signal processing circuit according to item 1.