KR0138153B1 - A shading compensation circuit - Google Patents

Abstract

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Description

Shading phenomenon correction device

1 is a circuit diagram of a shading correction device according to the prior art,

2 is a block diagram of a shading correction device according to the present invention;

3 is a detailed circuit diagram used to understand the operation of the shading corrector block diagram shown in FIG.

* Description of the symbols for the main parts of the drawings *

10 ... CCD sensor part 20 ... Sample / hold circuit part

30. Peak value detector

40.Shading Correction

The present invention relates to a shading correction device, and more particularly, to the document reading with an image scanner and a facsimile using a fluorescent lamp as a light source, the COS ⁴ ? The present invention relates to a shading phenomenon correcting apparatus which obtains a clearer and more accurate image signal by correcting a shading phenomenon in which the amount of ambient light is lower than that of a fluorescent lamp due to its own characteristics and illuminance hunting.

The shading phenomenon correction apparatus generally used constitutes a circuit as shown in FIG. Detecting a white level of the image signal from the white level detecting means (10) to the white level detecting means 10 outputs the comparison by the comparator to remove the shading component and the image signal (V _S) through (20). The back level detecting means 10 is composed of a diode D, a capacitor C and a resistor R. The time constant Z during charging is reduced and the time constant Z during discharge is converted to the capacitor C. And resistance (R).

However, the shading phenomenon correction apparatus when the black level range of the image signal (V _S) is small, but sikijineun impair the effective ingredient of the image signal (V _S) the black level range of the image signal (V _S) larger capacitor and a resistor If the discharge time constant Z of (R) is small, the effective component of the image signal is damaged and only the shading component cannot be removed accurately.

In addition, manufacturers are manufacturing one-chip image processors that customize the image preprocessing unit consisting of shading correction circuits, sample / hold circuits, A / D conversion circuits, and S / P conversion circuits. There was a problem with constraints.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object thereof is to obtain a clear and accurate image signal by correcting shading phenomena which occur during illuminance hunting or fluorescent imaging of fluorescent lamps used in an image scanner and a facsimile.

In addition, since shading correction is performed before conversion from an analog signal to a digital signal, there is another object to construct a shading correction device at a very low price since no restriction is applied to the subsequent signal processing of the shading correction device.

In order to achieve the above object, the present invention provides a CCD sensor unit for reading a shading distortion signal, a sample / hold circuit unit for converting a shading distortion signal, which is an analog signal, to a voltage which is maintained at a constant level for a gate time; A peak value detection unit for increasing the shading distortion signal until a peak value of a constant level voltage through the sample / hold circuit unit is detected to have an output value of various levels from a white level to a black level; And a shading correction unit configured to detect a peak value from the peak value detection unit and compare the image signal with a video signal to synchronize the video signal with the peak value to correct a shading phenomenon. Shading phenomenon correction device.

Hereinafter will be described in detail with reference to the accompanying drawings.

As shown in FIG. 2, which shows a block diagram of the present invention, the shading phenomenon correction apparatus according to the present invention includes a CCD sensor unit 10 for reading out shading distortion signals based on a completely back level. The sample / hold circuit unit 20 converts the shading distortion signal, which is an analog signal, to a voltage maintaining a constant level for the gate time, and increases the shading distortion signal that has passed through the sample / hold circuit unit 20. A peak value detector 30 having a plurality of output values from level to black level, and a peak value detected by the peak value detector 30 to compare with the video signal A shading correction unit 40 stores a counter output when two inputs are the same and synchronizes and corrects a shading phenomenon when an image signal when scanning is input.

3 is a circuit diagram of an embodiment shown in order to explain the second diagram in more detail. The CCD sensor unit 10 reads the shading distortion signal based on the full back level, and converts the shading distortion signal, which is an analog signal, to the constant level voltage during the gate time in the sample / holder circuit unit 20 by using a comparator ( At the same time, the output of the comparator 35 increases the count value of the counter 31, thereby degrading the CMOS switch 33 connected to the resistance string 34 by the decoder 32. They are switched in turn. First, the outputs of the resistor string stage 34 resistors R ₀ , ..., R _n-1 , R _n , R _{n + 1} on the black level VBL side are sequentially is changed toward the white level by the comparator 35 operates when the same as the image signal (V _S) to stop the count of counter 31. The resistor string (string) output at this time is a peak (尖頭) values of the image signals (V _S). After detecting the peak value of the off-set voltage of the comparator 35 using the OP amplifier 36 to zero the off-set error, the shading correction circuit unit 40 reads the Beck-level original. The CMOS switch 44 is switched so that the shading distortion signal obtained by the step is equal to the output of the resistance string 45.

That is, when the shading distortion signal and the resistance string (45) output are compared by the comparator 46, and the shading distortion signal is large, the NAND gate 48 is activated and up counted so that the resistance string (45) output is output. If the shading distortion signal is small and the shading distortion signal is small, the up / down counter 41 is operated to make the OR gate 49 active and down count to reduce the resistance string 45 output. (44) is switched.

At this time, the shading distortion signal is resistor string (string), (45) and then sewn to remember the output when equal the output up / down counter 41 to the RAM (42), when the image signal (V _S) input the up / reference of the down counter 41 outputs the image signal (V _S) synchronous to read (read) the RAM (42) for the resistor string (string), (45) a comparator (46) reproduces the shading distortion signal to the output of the ( reference) to perform shading correction.

The reproduced distortion signal includes the off-set voltage of the comparator 46, but the off-set error can be zeroed by using the OP amplifier 47 as in the peak value detector 30. .

As described above, an apparatus for correcting the shading phenomenon in reading an original using a fluorescent lamp as a light source may be regarded as an essential condition.

Of course, a light source without shading can be used, such as a halogen lamp, but since there is a significant difference in price, OA devices that require a light source use fluorescent lamps.

In addition, semiconductor manufacturers are customizing the image preprocessing unit into a single chip, but they are expensive and have a lot of limitations on the configuration of peripheral circuits.

The shading phenomenon correction apparatus of the present invention can be configured at a very low price, and since shading correction is performed before converting an analog video signal into a digital signal, resistance is not applied in performing signal processing at the rear end of the shading phenomenon correction apparatus. Since the string output value is also adjustable in arbitrary steps, there is an advantage in that accurate and precise shading correction can be performed without damaging the effective component of the image signal.

Claims (2)

A CCD sensor unit reading a shading distortion signal; A sample / hold circuit unit for converting a shading distortion signal, which is an analog signal, to a voltage maintaining a constant level for a gate time; A counter, a decoder, a CMOS switch, a resistance string stage, and a comparator, and decodes a count value that is sequentially increased to select the CMOS switch to sequentially increase the output of the resistance string stage via the selected CMOS switch, A peak value detector for detecting a peak value of the output of the resistance string stage when the output of the string stage and the input signal through the sample / hold circuit unit match; And The shading correction unit compares the peak value detected by the peak value detection unit with the shading distortion signal based on the full back level, stores the comparison information in the memory, and corrects the input image signal using the comparison information. Shading phenomenon correction apparatus characterized in that. The shading corrector of claim 1, wherein the shading corrector A counter, a decoder, a CMOS switch, a resistance string stage, a RAM, and a comparator, and compares the peak value detected by the peak value detector with a shading distortion signal based on a full back level, and if the shading distortion signal is large, When the shading distortion signal input to the comparator coincides with the output value of the resistance string terminal while increasing the output value of the input signal and increasing the output value of the resistance string stage, the shading distortion signal is small. And storing an up / down count value in the RAM and performing shading correction using an up / down count value stored in the RAM when an image signal is input.

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