JPH058620B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a method for correcting an input image signal in a facsimile device, an image scanning recording device for plate making, etc. The present invention relates to an image signal correction method for correcting the influence on an image signal caused by.

(Description of Background Art) For example, in a conventional image scanning recording device for plate making, a light beam from a reading laser is converted into scanning light by a scanning optical system, and the reflected light of this scanning light from a document is converted into scanning light by a scanning optical system. The light is collected by an optical fiber, and then incident on a photomultiplier tube for photoelectric conversion to obtain an image signal. After that, the image signal is clocked into the A/D by the clock signal generated from the clock signal generation circuit.
The converter is operated to digitize the above image signal.

The digital image signal obtained in this way is subjected to image processing such as gradation correction and sharpness correction, and then converted to a halftone signal.Based on this signal, the recording laser beam is modulated to produce a plate-making film. It is now being scanned and recorded.

(Problems to be Solved) The drawback of the image information reading device in the image scanning and recording device as described above is that, as illustrated in FIG. For example, since the length of the optical fiber 4 condensing light onto the photomultiplier tube 3 is not uniform in the main scanning direction Due to the difference in sensitivity depending on the image quality and the unevenness of the sensitivity distribution on the light receiving surface of the photomultiplier tube 3, unevenness occurs in the reading sensitivity in the main scanning direction X even when scanning originals with the same density. .

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems in an image reading device used in an image scanning reading/recording device, etc., and to solve the problem of the sensitivity distribution of the input system including the optical scanning system and the light receiving system. It is an object of the present invention to provide an image reading sensitivity distribution correction method that can obtain a digitized image signal in which the influence of uniformity is corrected.

(Means for Solving Problems) The basic principle of the present invention is that in an N-bit A/D converter to which a reference voltage is externally applied, the reference voltage is VR, the input analog signal voltage is VI, and the output digital value is Letting DO be the reference voltage ^VR .
By inputting a voltage VR (x) corresponding to the image reading sensitivity with respect to the position x of the light beam in the main scanning direction in synchronization with the main scanning of the image of the document, etc., the sensitivity unevenness is corrected. A digitized image signal is obtained from the output of the A/D converter.

Therefore, in order to achieve the object of the present invention, the image reading sensitivity distribution correction method of the present invention scans an image and digitizes a time-series image signal according to the scanning order using an A/D converter. To do this, set the data _A1 corresponding to the peak output value of the A/D converter with respect to the reference voltage input, pre-scan the reference document in advance, and calculate each of the information values obtained by scanning multiple times in the main scanning direction. Each average value A for each pixel is determined, and when the peak value of each average value A determined for each pixel position is set to A ₀ , each average value A is multiplied by A ₁ /A ₀ to calculate the scanning plane of the image. By calculating and storing a reading sensitivity distribution correction value for the digitized image signal, reading it out in synchronization with the scanning, and using it as the reference voltage of the A/D converter, it is possible to eliminate the difference in the digitized image signal due to uneven reading sensitivity. It is characterized by correcting the influence.

(Description of Embodiment) FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, an analog image signal VI having non-uniform reading sensitivity is inputted to an analog image signal input terminal 11 from the photomultiplier tube 3 of the image information reading device shown in FIG. . The image signal VI is digitized by an A/D converter 12 operated by a clock signal from a reference clock generating circuit 13 and stored in a line memory 14. As the line memory 14, for example, when the method of the present invention is applied to the image scanning recording device described above, it is preferable to use a line memory device provided for guiding the image information signal to the image sharpness correction circuit. suitable.

Writing and reading of image signals to and from the line memory 14 are controlled by an address counter 15 using the clock signal from the clock generation circuit 13 as a reference.
address designation or by the central processing unit 16, and these are switched by the address multiplexer 17. When preparing to correct the reading sensitivity distribution, image signals are written into the line memory 14 by addressing the address counter 15 and read by addressing the central processing unit 16. A correction value for reading sensitivity is calculated by the processing device 16 and stored in the correction memory 18. Writing and reading control of the correction memory 18 is performed by the central processing unit 16 at the time of writing.
Address designation and readout are performed by address designation of the address counter 19 based on the clock signal /N from the clock generation circuit 13, and these are switched by the address multiplexer 20. The latch circuit 21 is the correction memory 1
The correction value read from 8 is latched by the /N clock signal. This latch value is determined by the D/A converter 22.
The analog output VR of this D/A converter 22 is led to the reference voltage input terminal as the reference voltage of the A/D converter 12. In addition,
When the present invention is applied to an image scanning recording device, a part of the beam light for scanning the image of the original is divided, and a grating or the like is scanned with the divided scanning light to achieve the main scanning speed. By supplying a grid signal with a corresponding period to the clock generation circuit 13 and driving it, a clock signal synchronized with the grid signal is generated, and this clock signal is used to control the A/D.
Converter 12 and address counter 16 are driven. At the same time, a clock signal of /N (N is an integer) is generated, and this clock signal is guided to the address counter 19 and the latch circuit 21, so that the operation period of these is set as the operation period of the A/D converter 12 and the address counter 15. /N times.

FIG. 2 is a flowchart for explaining the procedure for correcting uneven sensitivity.

When the operation starts in step 30, the central processing unit 16 outputs the peak value ^2N according to a predetermined program.
The data A1 corresponding to ₁ is written into the correction memory (step 31).

Next, an original having a uniform reference density, for example a white original, is scanned multiple times by the image reading device (step 32). The image signal VI of multiple lines obtained by this scanning is led to the A/D converter 12, and in synchronization with it, the data _A1 is read out from the correction memory 18, and the latch circuit 21 and the D/A converter 22 are The reference voltage VR is supplied to the A/D converter 12 via the reference voltage VR, and A/D conversion is performed in sequence (step 33). The image signal thus digitized is written into the line memory 14. This is taken into the central processing unit 16, and the average value of the information values obtained by scanning multiple times is determined for each pixel in the main scanning direction, and the peak value initially determined is determined using this average value.
_A1 is calibrated for each pixel position to determine a sensitivity distribution correction value (step 34). This calibration is performed by calculating the peak value of each average value obtained for each pixel position.
When A ₀ , this is done by multiplying each average value A by A ₁ /A ₀ .

By writing the sensitivity distribution correction value calculated in this way into the correction memory 18 (step 35), preparations for correction of sensitivity unevenness are completed (step 36).
do.

After completing the preparation in this way, the image signal is led from the image reading device to the A/D converter 12, and the image information of the pixels in the scanning direction of the image signal is sent from the correction memory 18 via the latch circuit 21. At a timing corresponding to digitization, the correction value for the position corresponding to the pixel position is stored in the correction memory 18.
The digitized image signal guided to the line memory 14 by being read from the digitized image signal and applied as a reference voltage to the A/D converter 12 has been corrected for sensitivity distribution unevenness in the document reading system.

In this embodiment, the operation of the correction memory 18 and the latch circuit 21 is driven by a clock signal having a frequency of /N. Since the reading sensitivity distribution characteristic of a document reading device is a curve that changes with relatively smooth characteristics in the main scanning direction, when obtaining correction values at each position in the scanning direction by high-speed sampling, Since there is a possibility that the correction value may include a noise component on a white document and fluctuate greatly, the purpose is to suppress this influence to a minimum. In addition, the reference original is not limited to a white original, and may be a black original. However, when a white original is used, an image signal with a good S/N can be obtained, so reading sensitivity distribution information can be obtained. This method is more convenient than other monochrome originals in that it can be taken out with high precision.

Once the reading sensitivity correction value is stored in the correction memory in this way, a desired original is placed in place of the white original, main scanning is performed as described above, and the original is moved perpendicular to the main scanning direction. A two-dimensional scan is performed with a secondary scan. When reading out the original image, if the writing and reading control of the line memory 14 is performed sequentially by specifying the addresses of the address counter 15, the line memory 14 functions as a line memory for the sharpness correction device as described above. , it is possible to introduce an image to the image recording device that is not affected by unevenness in reading sensitivity with respect to an image such as a document, and it is also possible to correct sharpness with high precision.

Note that the method of the present invention is not limited to the above-described embodiments, and can be implemented for correction of reading sensitivity with respect to image scanning position in any image reading device.

Additionally, if the reading sensitivity changes over time, you can calculate multiple reading sensitivity correction values in advance, store them in the correction memory, and change the correction values as time passes. It is possible to appropriately correct the reading sensitivity distribution.

(Effects of the Invention) As explained in detail above, according to the method of the present invention, an image can be obtained in which unevenness in reading sensitivity due to differences in image scanning positions in the image reading device is corrected, regardless of the image scanning method in the image reading device. I can get a signal. In particular, when applied as part of the image processing system of the image scanning and recording device described above, the line memory device for sharpness correction can also be used to implement the method of the present invention, so it can be implemented extremely economically. Moreover, recording plate making can be performed without reducing the quality of the recorded image due to uneven sensitivity of the original reading device in the main scanning direction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the method of the present invention, FIG. 2 is a flowchart for explaining the operation when setting a correction value in the embodiment shown in FIG. 1, and FIG. FIG. 4, which is an explanatory diagram of problems of an image reading device in an image scanning recording device, etc., is an example of the distribution characteristic of the amount of light received in the main scanning direction in an optical scanning reading device. 11... Image signal input terminal, 12... A/D converter, 13... Clock generation circuit, 14... Line memory, 15, 19... Address counter, 16... Central processing unit, 17, 20... Address multiplexer, 18... Correction memory , 21...Latch circuit, 22
...D/A converter.

Claims (1)

[Claims] 1. When an A/D converter digitizes a time-series image signal according to the scanning order by scanning an image, the peak output of the A/D converter with respect to a reference voltage input is Set the data _A1 corresponding to the value, pre-scan the reference document in advance, find the average value A for each pixel in the main scanning direction of the information values obtained by scanning multiple times, and find it for each pixel position. The peak value of each average value is
When A ₀ , a reading sensitivity distribution correction value for the scanning plane of the image is calculated and stored by multiplying each average value A by A ₁ /A ₀ , and read out in synchronization with the scanning to An image reading sensitivity distribution correction method characterized in that the influence of non-uniform reading sensitivity on a digitized image signal is corrected by using the voltage as a reference voltage of an A/D converter.