JPH02179069A - Correction method for picture read signal - Google Patents

Abstract

PURPOSE:To obtain a dark current in response to a read state and to attain accurate correction by obtaining the output signal of a blind picture element for each read line of a line sensor and correcting the read signal of the line by a mean value. CONSTITUTION:The read signal of a line sensor 1 is converted into a digital signal RS and inputted to an adder 4 and a subtractor 7. A sum signal AS of the adder 4 is inputted to a latch circuit 5, the added result LS by 8-bit is inputted to the latch circuit 6 synchronously with a picture element clock PC, the addition result LS is set according to the sum result set pulse SP and the average data LAS is inputted to the subtractor 7. The mean value ALS is subtracted from the read signal RS at the subtractor 7 to correct the dark current and the result is outputted as a picture read signal PR.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial Application Field) The present invention relates to a method for correcting an image reading signal when an image is optically read by a line sensor such as a CCD.

(Prior Art) As a method of correcting the dark current of a solid-state image sensor such as a line sensor, there is a method described in Japanese Patent Application Laid-Open No. 53-123617. In this method, the light source is turned off and the gf4
The current is determined and stored in a memory, and thereafter the light source is turned on and the stored striking current value is subtracted from the signal at the time of image reading to obtain a corrected image reading signal. In addition, in the correction method described in Japanese Patent Application Laid-open No. 180377/1984, the 01N current is obtained by representing the data of one gummy pixel, and this IQ current value is subtracted from the image reading signal to obtain the image reading signal. .

(Problems to be Solved by the Invention) The former method described above (Japanese Unexamined Patent Publication No. 53-123617) involves the complexity of turning off and turning on the light source, and - Since it is used as a correction standard, there is a drawback that accurate correction cannot be performed when the brightness of the light source changes. In addition, in the latter method (Japanese Patent Application Laid-open No. 180377/1983), the dark current value is determined using one pixel, so it is incompletely able to deal with variations in each pixel and measurement errors due to noise, and the dark current value is However, there is a drawback that accurate correction cannot be made.

As described above, the photoelectric characteristics of conventional solid-state image sensors have large variations in the characteristics at dark levels, so correct correction is not performed, and in the case of line sensors, streaks appear especially in the sub-scanning direction. There are drawbacks.

This invention was made due to the circumstances mentioned above,
The purpose of this invention is to accurately determine the dark current value using multiple blind pixels each time one line of the line sensor is read.
It is an object of the present invention to provide a method for correcting an image reading signal, which allows accurate correction to be performed on an image signal for each line at all times.

Structure of the Invention: (Means for Solving the Problems) The present invention relates to a method for correcting an image reading signal, and the above object of the present invention is to correct a plurality of lines of the line sensor when reading an image line by line with a line sensor. This is achieved by determining the average value of the blind pixels, and using the average value to calculate and output the reading signal of the image.

(Function) As shown in FIG. 3, the line sensor 1 made of a CCD, etc. has blind pixels BG for several pixels (for example, 155 pixels) from both ends, which do not have a sensor function, and several pixels toward the inside thereof. (For example, it has a dummy pixel OC area with a 155-pixel light blocking mask IA arranged on the surface, and the other central part is the reading pixel RP. Normally, the reading pixel RP is used to capture images. It outputs an image reading signal according to the amount of reading light received.

Conventionally, 9f4 TLQ was measured using a dummy pixel DC placed on the surface of the mask I, and this dark current was used to correct the read signal. The signal of the blind pixel BC, which is provided at both ends and does not have a sensor function, is used as a signal for correcting the u total current, and the average value of a plurality of blind pixels is used.This average value data is used to determine the reading pixel R.
The image reading signal from P is corrected and output. Since the output of the blind pixel BC is a signal in a state where light is completely blocked and is an average value, it is possible to accurately correct image reading, and it also prevents streaks from appearing in the sub-scanning direction when reproducing images. do not have.

(Embodiment) Fig. 1 shows an example of a device for realizing the method of this invention, in which the read signal of the line sensor l is passed through an amplifier 2 and output to ^/D.
The converter 3 converts it into a digital signal R5 (for example, 8 bits), outputs it, and inputs it to an adder 4 and a subtracter 7.

The addition signal ^S (for example, 11 bits) from the adder 4 is input to the latch circuit 5, and is added by 8 bits in synchronization with the pixel clock PC as shown in FIG. 2 from the timing generation circuit 8. This addition result tS (for example, 11 bits) is input to the latch circuit 6 at the next stage. The latch circuits 5 and 6 are each cleared by a shift pulse LSP, and the latch circuit 6 sets the addition result LS of the latch circuit 5 in the latch circuit 6 in accordance with the addition result set pulse SP shown in FIG. , average value of added data,
That is, the upper 8 bits of the signal ALS are input to the subtracter 7.

Here, the pixel state of the line sensor 1 is as shown in FIG.
Output data for several pixels of C can be read and added, and the latch circuit 6 outputs an average value ALS for eight pixels of blind pixels BC every time one line is scanned. Then, the read signal when the image is read by the read pixel RP of the line sensor l is inputted to the subtracter 7 via the D/D converter 3, and the average value ALS is subtracted from the read signal +is to correct the dark current. This will be output as an image reading signal PR.

In the above embodiment, at the beginning of reading one line of the line sensor, the average value of the blind pixels is calculated and the reading signal of the reading pixel RP of the line is corrected. The dark current may be corrected by calculating the average value in the blind pixel BG and subtracting it when reading the next line. Further, the number of pixels for which the average value of the blind pixels is determined may be arbitrary, and the correction may be performed by determining the average value of several pixels. Furthermore, although the solid-state imaging device has been described using a line sensor as an example, it is also applicable to an area sensor in principle.

Effects of the Invention: As described above, according to the correction method of the present invention, the average value of the output signals of the blind pixels is obtained for each line read by the line sensor, and the read signal of the line is corrected using this average value. As a result, the bright current can be determined accurately according to the reading condition, since the correction is not affected by measurement errors due to pixel-by-pixel variations or noise, and it is possible to calculate the bright current accurately according to the reading condition. It is also possible to perform accurate corrections.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an apparatus for realizing the method of the present invention, FIG. 2 is a timing chart showing an example of its operation, and FIG. 3 is a diagram showing an example of the pixel arrangement of a line sensor. 1...Line sensor, 2...Amplifier, 3...^1
0 conversion 4...Adder, 5.6...Latch circuit, 7.
...Subtraction 8...Timing generation circuit.

Claims (1)

[Claims] 1. When reading an image line by line with a line sensor, find the average value of a plurality of blind pixels of the line sensor,
A method for correcting an image read signal, characterized in that the image read signal is calculated and output using the average value.