JPH03126373A - Black level correction means - Google Patents

Abstract

PURPOSE:To obtain sufficient picture quality with simple constitution and less capacity required for a memory by providing a correction data memory for each picture element of odd order number and even order number of photoelectric conversion elements. CONSTITUTION:Plural outputs of a light shield section of a line sensor 1 are read by an A/D converter 3 and the data is subject to proper processing (averaging processing for odd and even number order) at a correction data generating circuit 6 and the data is stored in a memory 7 storing an odd number correction data and in a memory 8 storing an even number correction data by odd and even number. When an original is read, an odd number correction data is selected to an odd number picture element and an even number correction data is selected to an even number picture element by an odd/even number selection circuit 9, the data is subject to subtraction or addition to correct the black level. Thus, the characteristic specific to odd and even number picture elements is absorbed and sufficient picture quality is obtained with a simple method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to black level correction of a document reading device using a line sensor or the like.

[Prior Art] FIG. 3 is a block diagram of a conventional black level correction circuit. When this circuit is applied to a document reading device that irradiates light onto a document and detects the reflected light using a photoelectric conversion element, the analog signal from the photoelectric conversion element 1 is transmitted to the operational amplifier 21.
etc. to a predetermined signal level, and then AD converter 3
It is common to have a configuration in which input is made to Here, since the photoelectric conversion element 1, operational amplifier 21, etc. have temperature characteristics and change over time, the lowest and highest level signals input to the AD converter 3 are higher than the (-) reference voltage of the AD converter 3, or (+) ) The level is adjusted by offsetting it to a level lower than the reference. Since the digital output of the AD converter 3 also has an offset for the reason mentioned above, subsequent processing is performed by subtracting or adding this offset value (correction data) stored in advance. This pre-stored data here is the dark output without any light input to the sensor 1, but conventionally this data has been taken as a representative value of the output of the limited light shield part of the sensor 1, or as a representative value of the output of the limited optical shield part of the sensor 1, or If the situation permitted, the dark output values of all pixels were sampled.

[Problems and Objectives to be Solved by the Invention] However, if the representative output value of a limited light shield section is used for all pixels, for example, in a dual channel CCD line sensor, the transfer section is used separately for odd and even pixels. Therefore, each has different characteristics and a unique tendency. This has the problem that streaks appear on the image at every other pixel in the sub-scanning direction, which significantly impairs the image quality.

Furthermore, since a large-capacity memory is required to store correction data for all pixels of the sensor, the circuit configuration becomes complicated, leading to an increase in cost.

SUMMARY OF THE INVENTION The present invention is intended to solve these conventional problems, and it is an object of the present invention to provide a black level correction means that requires less memory capacity and can obtain sufficient image quality with a simple configuration. be.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes a photoelectric conversion element for converting light reflected on a document surface into an electrical signal, and has a low and uniform reflectance by the photoelectric conversion element. The correction data obtained from the photoelectric conversion data of the reflected light on the reflective surface, the photoelectric conversion data when the light source is turned off, or the photoelectric conversion data of the optical shield part of the sensor is stored in the memory, and when actually reading the document, In black level correction in which image data from the photoelectric conversion element is corrected using correction data stored in the memory, a memory for correction data is provided on each side of odd-numbered and even-numbered pixels of the photoelectric conversion element. It is characterized by

[Operation] As described above, by having correction data for odd and even pixels, characteristics peculiar to odd and even pixels can be absorbed and sufficient image quality can be obtained with a simple method.

[Example] Examples of the present invention will be described below based on the drawings. 1st
The figure is a block diagram of the main components of the present invention. In FIG.
A photoelectric conversion element (line sensor) such as an OD, 2 a sensor control circuit that generates a driving pulse for the line sensor 1, 3 an A/D converter that converts the photoelectric conversion output of the line sensor 1 into digital data for each pixel; 6 is a circuit for creating correction data for odd and even pixels, 7 is a memory that stores the odd number correction data created in 6, 8 is also stored in the memory for even numbers, and 9 is used to read odd and even numbers. A selection circuit 10 selects which correction data to use, and a correction circuit 10 performs addition and subtraction for black level correction. Furthermore,
5 is a clock generation circuit that generates clock pulses used in this system, and 4 is a control circuit that receives the output of the clock generation circuit 5 and performs various controls. The operation of the embodiment configured as described above is as follows.

First, the procedure for determining correction data will be explained.

A plurality of outputs from the optical shield section of the line sensor 1 are read by the A/D converter 3. This data is subjected to appropriate processing (for example, averaging processing for each odd number and each even number) in the correction data creation circuit 6, and is stored on the odd and even numbers side.

Next, when actually reading the original, the odd-even selection circuit 9 selects correction data for odd numbers for odd-numbered pixels and for even-numbered pixels for even-numbered pixels, and performs subtraction or addition to correct the black level.

The correction explained above is based on the use of the light shield part of the sensor, but it is also possible to use the effective pixel output of the sensor due to the light reflected from the low-reflectance uniform reflective surface or the effective pixel output of the sensor when the lamp is turned off. The present invention is also effective when obtaining data.

FIG. 2 is a block diagram of the entire document reading device using the present invention, in which the correction data creation circuit is the CPU 16.
It also controls the entire document reading device. 1
5 is an image processing circuit such as binarization processing, 11 is a light source for reading the original, 12 is a control circuit for the light source 11, 18 is a system RAM, and 17 is an R containing programs and various data.
OM, 19 is an interface with an external computer, etc.
Reference numeral 14 denotes a control unit for controlling the sub-scanning direction of the document and the sensor.

Reference numeral 13 denotes a black level correction circuit which internally has a memory for correction data for odd and even numbers as a register.

In this example, more flexible processing is possible. For example, when creating correction data using reflected light from a low-reflectance uniform reflecting surface, instead of using the same location, you can use reflected light from a different location. The effects of dirt on the uniform reflective surface can also be reduced.

[Effects of the Invention] As described above, the present invention has the advantage that sufficient image quality can be obtained with a simple configuration that requires less memory capacity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main components in the present invention. FIG. 2 is a block diagram of a document reading device according to the present invention. FIG. 3 is a block diagram of a conventional black level correction circuit. 1... Photoelectric conversion element (line sensor) 2... ３　・・ ４　・・ 5　・・ 6 ・・ 7・・・ 8・・・ 9　・・ 10・ 11・ 12・ 13・ 14・ 15・ 16・ 17・ 18・ l　9　・ 20・ 21. Sensor drive circuit A/D converter Control circuit for the entire correction circuit clock generation circuit Correction data creation circuit Correction data memory for odd numbered pixels Correction data memory for even pixels Odd/even correction data selection circuit Black level correction circuit lamp Ramp system #circuit Black level correction circuit & control section Sub-scanning control section Image processing section pu System RAM Program & data ROM Interface with external circuit Correction data memory Operational amplifier

Claims (1)

[Scope of Claims] It has a photoelectric conversion element for converting light reflected from the document surface into an electrical signal, and photoelectric conversion data of the light reflected by the low reflectance uniform reflection surface by the photoelectric conversion element, or the light source is turned off. The correction data obtained from the photoelectric conversion data of the time or the photoelectric conversion data of the optical shield part of the sensor is stored in the memory, and when actually reading the document, the image data from the photoelectric conversion element is stored in the memory. In black level correction using correction data, a black level correction means comprising correction data memories separately for odd-numbered and even-numbered pixels of the photoelectric conversion element.