JPS5834677A - Mtf compensating system of picture information reader - Google Patents

Abstract

PURPOSE:To reduce the deterioration of picture quality in areas high in spatial frequency, by detecting the level difference between the one-element preceding and one-element succeeding picture elements of a corresponding picture element at every picture element of picture signals read and by operating corresponding compensating values. CONSTITUTION:An analog signal VIN obtained through an image sensor is converted into a digital signal (a) at an AD converter 1 and latched for every picture element by a latch circuit 2. Moreover, the preceding picture element of each picture element is latched at another latch circuit 3. The output of the latch circuit 2 is transferred to an up-down counter 4, and the counter 4 executes up-counting or down-counting so as to equalize the output of the counter 4 to the output of the latch circuit 3. In this way, level differences between two adjacent picture elements are obtained from a counter 6 as digital values and they are latched in a latch circuit 7. When the outputs of the counter 6 and the latch circuit 7 are inputted into an ROM 8, corresponding correction values stored in the ROM 8 are read out and compensated picture signals are obtained from an adder 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for solving the problem of M T F (ModuI
a-tion Transfer Function)
The present invention relates to an MTF correction method for an image information reading device that corrects a decrease in .

As shown in the opening of Figure 1, each pixel of image information on the manuscript is
B. In the case of a black and white pattern such as /, the image signal obtained from the image sensor of the image information reading device that reads this pattern has a high amplitude response in a high spatial frequency region where black and white patterns appear alternately, as shown in Figure A. becomes worse, and the white picture is usually a V of rep....

yA without responding until yA, and the black pixel also goes to ground potential GND
% lvB.

Here, the MTF of the image information reading device is expressed by the following formula: % As shown in FIG. 2, the MTF decreases as the spatial frequency becomes higher. In FIG. 2, ``open'' indicates a black and white pattern on the document, ``A'' indicates an image signal corresponding to each pixel of the black and white pattern, and . . . indicate an ideal image signal obtained when the reduction in MTF is removed.

The reason why the MTF of the image information reading device decreases as the spatial frequency increases as described above is due to the MTF of the optical system such as the image sensor and lens in the image information reading device.

Now, as described above, if a reproduced image is obtained from an image signal with a reduced MTF in a high spatial frequency region, the image quality will deteriorate in the high spatial frequency region.

That is, for example, when obtaining a black and white binary reproduced image,
This results in defects such as fine line parts becoming blurred or not being reproduced.

However, conventionally, no countermeasures have been taken against such image quality deterioration.

The present invention has been made in view of these circumstances, and is intended to electrically correct the decrease in MTF of an image information reading device caused by the optical system, and reduce the deterioration of the image quality of reproduced images in a high spatial frequency region. An object of the present invention is to provide an MTF correction method for an image information reading device that can perform the following steps.

In the present invention, attention is paid to the fact that the amount of decrease in MTF due to the optical system is an amount determined by calculation, and the MTF is corrected based on the principle shown in FIG.

That is, in FIG. 3, A is an image signal before correction, and v, , VB, and vo indicate the levels of three consecutive pixels, B and C, respectively. Now, when correcting pixel B, the level difference between the pixel B and the previous pixel (vA-II) and the level difference between the pixel B and the next pixel C (VCVB ) is detected. Since these level differences have a correlation with the spatial frequency of the original image, it is possible to know the amount of reduction in MTF caused by the optical system from these level differences. Therefore, by calculating a correction value corresponding to the amount of decrease in MTF and calculating this correction value with respect to the level VB of the currently targeted pixel B, the decrease in MTF due to the optical system can be electrically corrected. Can be done.

The image signal after this correction is shown at the beginning of Figure 3, and the level of pixel B is corrected to vB' (the calculation using the correction value is
(This is done in the direction of increasing the level difference between each pixel).

Next, the present invention will be explained in more detail based on embodiments shown in the drawings.

FIG. 4 shows an embodiment of a circuit for implementing the correction method according to the present invention. 1 is an analog image signal output output from an image sensor (not shown) of an image information reading device;
2 is a latch circuit that latches the output of the A/D converter 1, and 3 is a latch circuit that latches the output of the latch circuit 2. 4 is an up/down counter to which the contents of latch circuit 2 are transferred; 6 is latch circuit 3
A digital converter terminal that compares the output of the up/down counter 4 with the output of the up/down counter 4. 6 is a counter that counts the output of the comparator 5; 7 is a latch circuit that latches the output of the counter 6; 8 is the counter 6 and the latch 7;
ROMf,l, the above (
Correction values corresponding to various values that vA-VB) Oyohi (VCVB) can take are written. 9 is a digital adder that adds the output of the ROM 8 and the output of the launch circuit 3. Next, the operation of this circuit will be explained.

When the image sensor reads a document, the analog image signal VIN obtained from the sensor is converted into a digital image signal a by the A/D converter 1, and this digital image signal a is 11I! 0 is latched in the latch circuit 2 for every j pixel, and a certain pixel of the digital image signal a latched in the launch circuit 2 is transferred to the latch circuit 3 when the next pixel of the 4-pixel signal O is read, Same latch circuit 3
is latched to. Therefore, the latch circuit 3 latches a pixel that is one pixel before the pixel latched by the launch circuit 2.

Further, the contents latched by the latch circuit 2 are transferred to the up/down counter 4, and the comparator 5 compares the output of the up/down counter 4 with the output of the latch circuit 3. This comparison result is fed from the comparator 6 to the up/down counter 4, so that the four counters 4 count up or count down until the output of the counter 4 and the output of the latch circuit 3 become equal. This operation is repeated.

The counter 6 counts the number of steps until the output of the up/down counter 4 and the output of the latch circuit 3 become equal by counting the output of the comparator 6. Therefore, the latch circuit 3 now has pixel A1.
Assuming that the latch circuit 2 latches the image signal a of the pixel B, the level difference (vA-vB) between the pixel and the pixel B is obtained from the output of the color/receiver 6 as a differential value.

This level difference (VAVB) is then latched by the latch circuit 7.

Next, when the analog picture signal V of pixel C, which is one pixel after pixel B, arrives, the latch circuit 2 latches the digital picture signal a of pixel C, while the latch circuit 3 receives the digital picture signal of pixel B. Signal a is latched. Then, in the same manner as described above, from the output of the counter 6, the level difference (vcVn
) is obtained. Furthermore, by inputting the output of the counter 6 and the output of the launch circuit 7 to the ROMB as address inputs, the above (vA-vB) and (' VcVB
) is read from the ROMB.

Then, the correction value and the digital image signal a of pixel B output from the latch circuit 3 are added by the adder 9, so that the image signal of pixel B that has been corrected for MTF becomes V. Obtained as uT.

Thereafter, by repeating the same operation, correction to the MTF is successively performed for pixels after pixel C one after another.

In this embodiment, since various correction values are stored in the ROM, it is easy to set the correction values, and depending on the purpose of the reading device, correction values that emphasize the outline of the image may be It is also possible to calculate and store it in ROM.

In addition, in this embodiment, correction is performed by adding a correction value to the image signal to be corrected, but depending on how the correction value is set, the image signal to be corrected may be multiplied by the correction value, or the image signal to be corrected may be multiplied by the correction value. It goes without saying that correction can be performed by dividing the image signal to be corrected by the correction value.

Furthermore, although the two embodiments have shown the case of binary values of white and black, the present invention can also be applied to the case of reproducing halftones, and in this case, it is possible to obtain a reproduced image with density faithful to the original image. be able to.

As described above, the MTF correction method of the image information reading device according to the present invention calculates the novel difference between each pixel of the image signal obtained from the image information reading device and the pixel immediately before and after the pixel. By detecting these level differences and calculating a correction value corresponding to the level of the pixel, the decrease in MTF caused by the optical system can be electrically corrected, and the reproduction image r phenomenon in the high spatial frequency region can be corrected. This provides an excellent effect of reducing deterioration in image quality.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams showing the responsiveness of an image signal obtained from an image sensor to the spatial frequency of an original image, and FIG. 3 is an image information reading device according to the present invention: a mu/D converter; 2, 3...Latch circuit, 4...Up/down counter, 5...Digital comparator, 6...Counter, 77"...Latch Circuit, 8...ROM, 9...Digital adder. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Museum 2 Figure WA 3 rM

Claims (1)

[Claims] For each pixel of the image signal obtained from the image information reading device, the level difference between the pixel immediately before and after the pixel is detected, and the correction value corresponding to these level differences is calculated as the level of the pixel. M of the image information reading device is calculated for
M of an image information reading device characterized by correcting TF
TF correction method.