JPS6096076A - Device for correcting shading distortion - Google Patents

Abstract

PURPOSE:To execute shading correction, which is easy to be realized as a comparatively inexpensive integrated circuit and has high accuracy and stability by adopting an MOS type A/D convertor using a small chopper comparator of offset voltage as circuit constitution. CONSTITUTION:Prior to reading an original, reading and scanning of a white reference plate 5 is executed by a scanner 2 and a white reference scan signal is inputted in an A/D convertor 9, a correction coefficient M is read out from an ROM10 address which is designated by the white reference scan signal changed into a digital, and wrote in an address which is in correspondence to a picture element of an RAM11. Then an original 4 is transferred to a read position, and an original scan signal is inputted in a device 1 for correcting shading strain from the scanner 2. At this time, the RAM11 is operated in a read mode and outputs a correction coefficient by synchronizing with a read scan. An operator 12 performs multiplication of said correction coefficient and the original scan signal which is changed into digitals by the A/D convertor 9 and outputs the original picture information whose shading strain is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shading distortion correction device used in a document reading section of a facsimile machine.

Conventional configuration and its problems Signals obtained by scanning a document with a scanner used in the document reading section of a facsimile machine (referred to as a document scanning signal) are generally affected by uneven light intensity of the document illumination light source and light intensity of the optical system. It is subject to distortion due to unevenness, sensitivity variations in the image sensor, etc. (hereinafter, these distortions are collectively referred to as shading distortion). Therefore, in a document reading section of a facsimile machine, a shading distortion correction device is placed after the scanner to correct the shading distortion of the document scanning signal.

Such shading distortion correction devices are generally configured to convert an analog document scanning signal input from a scanner into a digital signal using an A/D converter, and then execute correction calculations. be. However, since such conventional devices employ bipolar A/D converters, they have the problems of high power consumption, high cost, and difficulty in integration.

The present invention solves the above-mentioned conventional problems, and aims to provide a complete shading distortion correction device that can be easily realized as a relatively inexpensive integrated circuit and that can perform highly accurate and stable shading distortion correction.

Structure of the Invention The present invention converts the A/D converter, which had been difficult to integrate in conventional devices, into a MOS, making it easier to integrate, and at the same time achieving sufficient performance comparable to when using a bipolar MU/D converter. The main feature is that an MO8 type A/D converter with a circuit configuration using a chopper type comparator with a small offset voltage is used so as to obtain correction accuracy.

More specifically, the shading distortion correction device of the present invention has a circuit configuration using all chopper type comparators.
It has an s-type A/D converter, ROM, RAM, and calculation 2g, and the white reference plate scanning signal 1 inputted from an external scanner is digitized by the above A/D converter, and the above R
By inputting the address signal to OM, the above RO
outputting an M direction correction coefficient, storing the same correction coefficient in the RAM, and then digitizing the original scanning signal input from the scanner with the A/D converter and inputting it to the arithmetic unit; At the same time, the correction coefficient is read from the RAM and input to the arithmetic unit, and the arithmetic unit calculates the original scanning signal and the correction coefficient, thereby correcting shading distortion on the original scanning signal.

Description of examples Embodiments of the present invention will be described below with reference to the drawings.

The figure is a schematic block diagram of a shading distortion correction device according to an embodiment of the present invention, and also shows a schematic configuration of a scanner. In this figure, 1 is a shading distortion correction device, and 2 is a scanner.

To explain the scanner 1, numeral 3 is a lamp for illuminating an original 4 or a white reference plate 5, and an image of the original 4 or white reference plate 5 illuminated by this lamp 3 is sent to a CCD via a lens 6. An image is formed on the light receiving surface of the image sensor 7, and an analog image signal (
The signal is photoelectrically converted into an original scanning signal (original scanning signal or white reference plate scanning signal). Main scanning for reading the original 4 or white reference plate 5 is performed by the CCD image sensor 7, and sub-scanning is performed by moving the original (sub-scanning for the white reference plate 5 is not performed.C, CD image sensor 7 The analog white reference plate scanning signal or original scanning signal outputted from the shading distortion correction device 1 is amplified by the amplifier 8 and then inputted to the shading distortion correction device 1 .

If the configuration of the shading distortion correction device 1 is explained, 9
is an MO8 type A/D with a circuit configuration using a chopper type comparator.
This converter converts the white reference plate scanning signal or original scanning signal input from the scanner 2 into a digital double signal.

10 is a ROM, 11 is a RAM, and 12 is an arithmetic unit.

The output signal of the A/D converter 9 is input to the ROM 10 as an address signal, and is also input to the arithmetic unit 12 as one operand data. The output signal (correction coefficient) of ROM10 is inputted to RAM1t as write data,
The output signal (correction coefficient) of the RAM 11 is input to the arithmetic unit 12 as the other operand data.

Next, the operation will be explained. Before reading the original, scanner 2
The white reference plate 6 is read and scanned, and a white reference plate scanning signal is input to the A/D converter 9.

A correction coefficient M determined by the following equation (1) is read from the address in the ROM 10 specified by the white reference plate scanning signal digitized by the A/D converter 9, and written to the address corresponding to the pixel in the RAM 11. .

Win x M/2n -C ・・・・・・・・・・・・・・・ (1) Here, Vin
is the value of the white reference plate scanning signal, n is the number of quantization bits, and C is a constant. This C corresponds to the lower limit value of the shading distortion correction range.

In this way, the correction coefficients for each pixel are sequentially determined, and the RA
The correction coefficients for one line are finally stored in the RAM 11. The white reference plate scanning signal is subjected to shading distortion determined by the state of the scanner 2 at that time, and the shading distortion is reflected in the correction coefficient in the RAM t1.

Thereafter, the original 4 is conveyed to the reading position, reading scanning of the original 4 is started, and an original scanning signal is input from the scanner 2 to the shading distortion correction device 1 .

At this time, the RAM 11 operates in the read mode and outputs the correction coefficient in synchronization with the read scan. This correction coefficient and A/
Multiplication with the original scanning signal digitized by the D converter 9 is executed in the computing unit 12, and the original scanning signal (original image information) subjected to shading distortion correction is sent to the computing unit 12.
It is output from

In general, the shading distortion characteristics of the scanner 2 tend to fluctuate considerably over time immediately after the lamp 3 is turned on, but the correction coefficients in the RAM 11 are determined from the white reference plate scanning signal immediately before the start of document reading. , which faithfully reflects the shading distortion characteristics of the scanner 2 when reading a document. Therefore, stable shading distortion correction is always performed. In addition, the MO8 type A/D converter has
There are circuit configurations that use a direct-coupled comparator and circuit configurations that use a chopper-type comparator.The former has a large input offset voltage, generally around csmV, and it is difficult to obtain quantization accuracy of 5 bits or more. However, in the latter case, high quantization precision of 5 bits or more can be easily obtained. However,
The A/D converter 9 has a circuit configuration using a chopper type comparator, and can obtain a quantization accuracy of 5 bits or more, so that highly accurate 7-edding distortion correction is possible.

Furthermore, in the past, the existence of a bipolar type MU/D converter with high power consumption was an obstacle to integration, but since the A/D converter 9 is a MOS type, the present shading distortion correction device 1 The entire structure or parts other than the RAM 11 can be easily integrated on one semiconductor chip.

Effects of the Invention As described above, according to the present invention, an MO8 type A/D converter with a chopper type comparator configuration that is suitable for integration and can obtain high quantization accuracy is used, so integration is easy and high precision is achieved. 7
It is possible to provide a shading distortion correction device capable of correcting aging distortion, and since the correction coefficients stored based on the white reference plate scanning signal input prior to reading the original are used for correction, stable shading distortion correction is always possible. Effects such as being made possible can be obtained.

[Brief explanation of the drawing]

The figure is a schematic block diagram showing a shading distortion correction device according to an embodiment of the present invention. 1... Shading distortion correction device, 2...
Scanner, 3...Lamp, 4...Document, 6...
...White reference plate, 6...Lens, 7...COD image sensor, 8...Amplifier, 9...M
O3 type A/D converter, 1o...ROM, 11...
...RAM, 12... Arithmetic unit.

Claims (1)

[Claims] It has an MO8 type A/D converter with a circuit configuration using a chopper type comparator, a ROM, a RAM, and an arithmetic unit.
The correction coefficient is output from the ROM by digitizing it with a converter and inputting it as an address signal to the ROM, and the correction coefficient Fl'f is stored in the RAM, and then input from the scanner. The original scanning signal is digitized by the A/D converter and inputted to the computing unit, and at the same time, the correction coefficient is read from the RAM and input to the computing unit 1.The computing unit converts it into the original scanning signal. By multiplying the above correction coefficient,