JPH0815309B2 - Image signal correction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal correction device that corrects sensitivity variations and light amount variations included in image signals obtained by scanning a document.

2. Description of the Related Art As shown in FIG. 3, a conventional device of this type has a document 1, a white reference surface 2, a light source 3 for irradiating them, a document 1 and a white reference surface 2. Image sensor 4 for scanning, A / D converter 5 for multi-level quantizing the sensor output, ROM 6 for receiving the output of the converter 5 and outputting a correction coefficient according to the input level, and the white reference RAM7 that stores the one line complement coefficient obtained by scanning surface 2
And a multiplier 8 which receives the output of the A / D converter 5 and the output of the RAM 7 and performs a multiplication process. Its behavior is
First, before illuminating the original 1 with the light source 3 and scanning it, the white reference surface 2 is scanned, and the obtained image signal A / D converter 5
After quantizing with, it is input to the ROM6.

Here, assuming that the image signal as shown in FIG. 4 (a) is obtained by scanning the white reference plane 2, the V ₁ level signal of the first pixel has a level of V _P / V ₁ . The coefficient is stored in the first pixel of the RAM 7.

Similarly, the coefficient of V _P / V _N is stored in the RAM 7 for all the pixels in one line.

On the other hand, the image signal obtained by scanning the original 1 is input to the X terminal of the multiplier 8, and at the same time, the correction coefficient signal (V _P / V _N ) of the same pixel output from the RAM 7 is output to the Y terminal. Is input to the device, where the multiplication process is performed.

Thus, for example, when the image signal obtained by scanning the original 1 has a waveform similar to that shown in FIG. 4A, when a signal having the waveform is input to the X terminal, the image signal shown in FIG. It is output from the multiplier 8 as a signal having a uniform waveform as shown in b).

In this way, the image signal in which the sensitivity variation and the light amount variation are corrected is taken out from the multiplier 8.

However, according to such a configuration, when dust or the like adheres to the white reference surface, the correction coefficient under the adhered state is calculated, so that the sensitivity difference is far greater than the actual sensitivity variation. Correction is applied, and white lines and black lines appear in the reproduced image,
There was a problem of causing deterioration of image quality.

As a solution to that problem, transfer the calculated correction coefficient to another jig without directly inputting it to RAM7, burn it to ROM, and connect that ROM to RAM7 There is a method in which correction can always be performed with a value such as calculation.

However, according to this method, when the light source, the image sensor, or the like causes a change over time, the correction coefficient cannot follow the ROM except to remake the ROM by using a jig.

The present invention has been made in view of the above problems, and can be immediately dealt with when a change with time occurs without being affected by dust or the like and without using a special jig. An object is to provide a signal correction device.

Means for Solving the Problems Reading means for reading a reference plate before scanning an original to obtain a reference image signal for image signal correction, and a rewritable memory for storing the reference image signal read by the reading means. If the level difference of the corresponding pixel between the previous reference image signal before being rewritten in this memory and the current reference image signal obtained by the reading means is within a predetermined value, the previous reference image signal stored in the memory is The current reference image signal is rewritten, the image signal is corrected based on this, and when the level difference is equal to or more than a predetermined value, an error is notified and the writing operation of the current reference image signal is enabled again, and the writing is performed. When not performed, a control means for correcting the image signal with the reference image signal stored in the memory is provided.

The present invention notifies an error when the level difference of the corresponding pixel between the previous reference image signal stored in the memory and the current reference image signal obtained by the reading means is equal to or more than a predetermined value. At the same time, the writing operation of the current reference image signal is enabled again, and when the rewriting is not performed, the image signal is corrected by the reference image signal stored in the memory.

Embodiment FIG. 1 is a schematic block diagram showing an embodiment of an image signal correction apparatus according to the present invention, in which 20 is an original and 21 is an original.
Is a reference plate for reading a reference image signal for image signal correction (for example, a white reference plate or a reference plate such as a white reference document paper (hereinafter referred to as a white reference plate), 22 is the original document 20 and the white reference plate. (White reference surface) Light source for illuminating 21, 23 is the original 20 and white reference plate
21 is an image sensor for scanning, 24 is a multi-value quantization of the sensor output signal obtained by the scanning of the image sensor 23
It is an A / D converter.

25 timing controller, an electrically rewritable non read only memory unless erasing information is stored 26 (electrically erasable rewriting read only memory), a memory 26, for example E ² PROM ( Electrically Erasabl
e and Programmable ROM) is suitable.
It is represented by E ² PROM.

The E ² PROM 26 writes the reference image signal (white reference image signal for image signal correction) obtained by scanning the white reference plate 21 only when specified by the timing control unit 25, and writes ( In the normal state where rewriting is not performed, the already written reference image signal is output without change. The reference image signal is not erased even when the power of the device is turned off.

An image signal (quantized signal) 27 obtained by scanning the document 20 is input to the X terminal and an output reference image signal of the E ² PROM 26 is input to the Y terminal 27, and sensitivity variations and This is an arithmetic unit that performs a correction calculation of the light amount variation.

28 compares the level difference between the reference signal already stored in the E ² PROM 26 and the current reference image signal obtained by scanning the white reference plate 21, and if the level difference exceeds a certain value, it is abnormal. It is a comparator that outputs a signal.

Reference numeral 29 is a display for displaying an abnormal state (to the effect that the reference image signal should be rewritten to the E ² PROM 26) in response to the input of the abnormal signal from the comparator 28.

Regarding the image signal correction device configured as described above,
The operation will be described below.

First, the white reference plate 21 under the condition that no dust is attached.
Is scanned by the image sensor 23. The output of the sensor 23 (reference image signal) is multi-valued quantized by the A / D converter 24 and input to the E ² PROM 26 at the following writing timing.

Here, an example of so-called writing timing in which the reference image signal is stored in the E ² PROM 26 is shown in FIG. In the figure, A to F show respective signals in the main part of FIG. 1, A is a clock synchronized with the reference image signal, B is a one-line synchronization signal, and both are timing control units. Entered in 25. Further, C is an output signal of the image sensor 23. D is an A / D conversion clock output from the timing control unit 25 to the A / D converter 24, E is an A / D converted reference image signal input from the A / D converter 24 to the E ² PROM 26, and F is It is an E ² PROM write pulse from the timing control unit 25. The write pulse width is generally longer than the reference image signal clock in many cases.

The timing control unit 25 performs the timing matching as shown in FIG. Then, the E ² PROM 26 writes and stores the reference image signal E only when the write pulse F is input from the timing control unit 25.

In the example of FIG. 2, one pixel is written by three reference image signal clocks. Therefore, in order to write the reference image signal to the E ² PROM 26, the first line is 1, 4,
The pixel lines of 7, ..., The second line is A / D converted to the pixel lines of 2, 5, 8, ..., The third line is the pixel lines of 3, 6, 9 ,. The reference picture signal E is sequentially written into the E ² PROM 26. Therefore, in this case, conversion of the reference image signal obtained by scanning the white reference plate 21 with the image sensor 23,
Writing requires a time of 3 lines.

In this way, after the A / D converted reference image signal E (corresponding to the correction coefficient) E is stored in the E ² PROM 26 for one line, the document 20 is actually scanned.

In the computing unit 27, the image signal (quantized signal) obtained by scanning the original document 20 is supplied to the X terminal, and the E ² PROM 26
The reference image signal E stored in is input to the Y terminal, and correction calculation of Z = X · V _P / Y (correction of sensitivity variation and light amount variation) is performed. Here, Z is the corrected image signal (output signal of the arithmetic unit 27), X is the image signal (quantized signal) input to the X terminal, and Y is the reference image signal E, V _P input to the Y terminal. Is the maximum level signal of the reference image signal E.

In this way, the image signal obtained by scanning the document 20 is corrected (correction of sensitivity variations and light amount variations) by the calculator 27 and output.

On the other hand, when the white reference plate 21 is scanned again before the original document 20 is scanned, the comparator 28 detects that the reference image signal of the same pixel is currently being scanned.
If the level difference with the reference image signal already stored in the E ² PROM is compared and the level difference is a certain value or more,
The abnormal signal is output to the display unit 29.

The display 29, which has received the abnormal signal, notifies the operator of the abnormal state. According to the notification, the operator cleans the white reference plate 21 and then again writes the reference image signal E to the E ² PROM 26.

Unless the above rewriting (rewriting) is performed, the E ² PROM
Reference numeral 26 indicates the number of times the original 20 is scanned thereafter, even if dust adheres to the white reference plate 21 or changes over time (of course, when these abnormalities occur, the display device 29
The reference image signal (correction coefficient) already stored is output to the computing unit 27 without being affected by any of them. Therefore, the calculator 27
It is possible to obtain a more stable output signal (an image signal in which variations in sensitivity and variations in light amount are corrected).

Further, as described above, when the abnormality occurs, the abnormal situation can be immediately dealt with by rewriting the reference image signal E to the E ² PROM 26 based on the notification from the display 29.

EFFECTS OF THE INVENTION As is apparent from the above description, according to the present invention, when the reference plate with dust or the like is read, the correspondence between the current reference image signal obtained here and the previous reference image signal stored in the memory is obtained. Since the level difference between the pixels is large, by notifying the error without rewriting the memory to the current reference image signal, without performing correction based on the reference image signal with dust or the like attached to the reference plate, It is possible to prevent white stripes, black stripes, and the like in the reproduced image due to such a reference plate, and it is possible to immediately take measures such as cleaning the reference plate.

Then, after cleaning the reference plate, it is possible to write the reference image signal again, so the reference image signal on a clean white reference plate after cleaning can be taken in, and the reproduction image caused by the reference plate can be reproduced. We can prevent weeping.

[Brief description of drawings]

FIG. 1 is a schematic configuration block diagram showing an embodiment of an image signal correcting apparatus according to the present invention, FIG. 2 is a signal waveform diagram (writing timing diagram) of a main part in FIG. 1, and FIG. 3 is a conventional image. 4 is a block diagram showing a schematic configuration of a signal correction device, FIGS. 4 (a) and 4 (b) are diagrams for explaining an operation of a main part of a conventional device, and FIG. 4 (a) is an image signal waveform diagram before correction. FIG. 3B is a waveform diagram of the image signal after correction. 20 …… Original, 21 …… Reference plate (white reference plate), 22 …… Light source,
23 …… image sensor, 24 …… A / D converter, 25 …… timing control unit, 26 …… electrical erasure rewritable read-only memory, 27 …… arithmetic unit, 28 …… comparator, 29 …… display vessel.

Claims (1)

[Claims] 1. A reading means for reading a reference plate before scanning an original to obtain a reference image signal for image signal correction, a rewritable memory for storing the reference image signal read by the reading means, and this memory. When the level difference of the corresponding pixel between the previous reference image signal before rewriting and the current reference image signal obtained by the reading means is within a predetermined value, the previous reference image signal stored in the memory is changed to the current reference image signal. The signal is rewritten, the image signal is corrected based on the signal, and when the level difference is equal to or larger than a predetermined value, an error is notified and the writing operation of the current reference image signal is enabled again, and writing is not performed. An image signal correction apparatus, which sometimes comprises a control unit for correcting an image signal with a reference image signal stored in a memory.