JPH04372278A - Picture signal correction device - Google Patents

Abstract

PURPOSE:To obtain a picture signal correction device able to correct shading distortion of a power supply while keeping correction accuracy of a white level. CONSTITUTION:An A/D converter 2 converts an analog picture signal ASIG into a digital picture signal DSIG. A memory 4 stores a reference white level by one line scanning of an image sensor for each picture element. A white level correction circuit 3 receives the digital picture signal DSIG and the reference white level and gives a carry signal CO of '1' to an OR gate 5 through overflow when the digital power supply DSIG is larger than the reference white level. In this case, the OR gate 5 outputs all '1s' regardless of an input from the white level correction circuit 3. Thus, the picture signal V is fixed to a most significant level (2R-1) of the white level. Thus, even when the digital picture signal DSIG is larger than the reference white level, it is avoided that the level of the power supply is swung largely toward the black level.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal correction device for correcting shading distortion in an image processing device such as a facsimile machine.

0002

2. Description of the Related Art In an image reading device using an image sensor, there are two types of distortion: gentle distortion caused by a decrease in the amount of light at both ends of a document due to the characteristics of the light source and lens, and high-frequency distortion caused by the characteristics of the image sensor. Since the image signal photoelectrically converted by such an image reading system contains the above-mentioned distortion, it is necessary to correct the distortion. As a device for correcting this distortion, there has been a shading distortion correction device.

FIG. 2 is a block diagram showing a conventional shading distortion correction device. Signal input terminal 1 receives an analog image signal ASIG from an image sensor (not shown).
is input. A/D converter 2 receives analog image signal AS
IG is converted into an n-bit (n is the number of quantization bits) digital image signal DSIG, which is supplied to the white level correction circuit 3. The memory 4 stores the level of each pixel (hereinafter referred to as the reference white level) for one line scan when a white reference document is actually read by the image sensor, and supplies this reference white level to the white level correction circuit 3. .

[0004] The white level correction circuit 3 performs correction for each pixel of the digital image signal DSIG based on the reference white level given from the memory 4 based on the equation shown below.

DSIG×(2n −1)/Reference white level=V where V
is the image signal after white level shading distortion correction, D
SIG is the value of digital image signal DSIG, 2n −1
is the value of the highest white level.

[0006]

Since the conventional shooting distortion correction device is constructed as described above, the digital image signal DSIG does not originally have a value larger than the reference white level. However, due to disturbances such as noise, A/
When the D converter 2 malfunctions and the digital image signal DSIG becomes a value larger than the reference white level, an overflow occurs in the white level correction circuit 3, and the image signal V after correcting the shading distortion of the white level becomes closer to the black level. There was a problem in that the camera would shake a lot and the white level correction accuracy would drop.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an image signal correction device that can correct shading distortion of an image signal while maintaining white level correction accuracy. purpose.

[0008]

[Means for Solving the Problems] An image signal correction device according to the present invention includes an A/D conversion means for converting an analog image signal from an image sensor into a digital image signal, and a reference for one line scanning of the image sensor. a storage means storing a white level; the storage means is connected to the storage means and the A/D conversion means; and the digital image signal is shaded using the digital image signal and the reference white level read from the storage means. an arithmetic processing means that performs arithmetic processing for performing distortion correction; and an arithmetic processing means that is connected to the arithmetic processing means and takes a logical sum of the arithmetic result from the arithmetic processing means and a carry signal of the arithmetic processing means. We are prepared.

[0009]

[Operation] In this invention, since the arithmetic means is provided to take the logical sum of the arithmetic result from the arithmetic processing means and the carry signal of the arithmetic processing means, even if the arithmetic processing means overflows, the output is white level is output.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of an image signal correction apparatus according to the present invention. The difference from the conventional device shown in FIG. 2 is that an OR gate 5 is newly provided, and the white level correction circuit 3 outputs a carry signal CO. The carry signal CO is “0” when the digital image signal DSIG given to the white level correction circuit 3 is smaller than the reference white level (that is, when no overflow occurs).
", becomes "1" when it becomes larger (that is, when an overflow occurs). One input of the OR gate 5 receives the digital image signal corrected by the white level correction circuit 3, and the other input receives the carry signal CO. The other configurations are the same as the conventional circuit.

Next, the operation will be explained. As before, the A/D converter 2 receives the applied analog image signal ASIG.
is converted into a digital image signal DSIG and provided to the white level correction circuit 3. At this time, the digital image signal DSIG
is smaller than the white reference level stored in the memory 4, no overflow occurs in the white level correction circuit 3;
The carry signal CO becomes "0". A digital image signal DSIG corrected by the white level correction circuit 3 is input to one input of the OR gate 5 . Therefore, the output of the white level correction circuit 3 is output from the OR gate 5 as it is.

On the other hand, when the digital image signal DSIG is higher than the reference white level stored in the memory 4, an overflow occurs in the white level correction circuit 3, and the carry signal CO becomes "1". This "1" is input to the other input of the OR gate 4. Therefore, regardless of the input from the white level correction circuit 3, the output of each OR gate 5 is "
1" is output. Therefore, the image signal V after shading correction has the highest white level (2n -1, that is (11...1)) regardless of the output of the white level correction circuit 3.
, so that the image signal V does not swing significantly toward the black level side as in the conventional case.

[0013]

[Effects of the Invention] As described above, according to the present invention, since the arithmetic means is provided for calculating the logical sum of the arithmetic result from the arithmetic processing means and the carry signal of the arithmetic processing means, the arithmetic processing means does not overflow. However, the highest white level of the digital image signal is output. As a result, it is possible to correct shading distortion of an image signal while maintaining white level correction accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an image signal correction device according to the present invention.

FIG. 2 is a block diagram showing a conventional shading distortion correction device.

[Explanation of symbols]

2 A/D converter 3 White level correction circuit 4 Memory 5 OR gate

Claims (1)

[Claims] 1. A/D conversion means for converting an analog image signal from an image sensor into a digital image signal;
storage means storing a reference white level for one line scan of the image sensor;
arithmetic processing means connected to the D conversion means and performing arithmetic processing for applying shading distortion correction to the digital image signal using the digital image signal and the reference white level read from the storage means; and the arithmetic processing An image signal correction device, comprising: arithmetic means connected to the arithmetic processing means for calculating a logical OR of the arithmetic result from the arithmetic processing means and a carry signal of the arithmetic processing means.