JPH0456477A - Method for correcting read picture signal - Google Patents

Abstract

PURPOSE:To execute an exact correction at all times by calculating a mean value in the case of reading the plural lines of plural blind picture elements in a line sensor, calculating and outputting the red signal of a picture by using the mean value. CONSTITUTION:According to a timing signal SRC from a timing generation circuit 8, the data of blind picture elements before 5 lines is outputted from a shift register 10 and subtracted from a current blind picture element output RS by a subtracter 14. This subtracted value is inputted to an adder 15 and an added signal AS is inputted to a latch circuit 16. Then, only the blind picture elements are added with the circuit 16 according to an integration clock GPC from the circuit 8, and the mean value ALS of an added data LS is held by a latch circuit 17 and subtracted from picture element signals, which are read out of line memories 11-13, by a subtracter 7 so as to correct an output signal PR. Thus, a dark current can be exactly calculated and exact correction is available.

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 dark current is corrected by turning off the light source. The dark current value is determined and stored in a memory, and thereafter the light source is turned on and the stored dark current value is subtracted from the signal at the time of image reading to obtain a corrected image reading signal. However, with this method, it is complicated to turn off and turn on the light source, and since the previously memorized dark current value is used as the reference for subsequent corrections, the dark current value fluctuates due to changes in environmental temperature, etc. In some cases, there is a drawback that accurate correction cannot be performed.

Furthermore, in the correction method described in Japanese Patent Application Laid-open No. 180377/1984, the dark current is obtained by representing the data of one dummy pixel, and this @current value is subtracted from the image reading signal to obtain the image reading signal. . However, since this method calculates the dark current value for one pixel, there are variations from pixel to pixel,
It has the disadvantage that it is incomplete in dealing with measurement errors due to noise, and it is not possible to accurately compensate for dark current.

In this way, the photoelectric characteristics of conventional solid-state image sensors vary widely 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 some drawbacks.

(Problems to be Solved by the Invention) Figure 3 shows an example of a device that solves the above problems (Patent Application No. 63-333839), in which the read signal of the line sensor 1 is passed through the amplifier 2 and converted into an A/D converter. digital signal R at device 3
5 (for example, 8 bits) and output, and adder 4
and is input to the subtracter 7. Addition signal AS of adder 4
(for example, 11 bits) is manually input to the latch circuit 5,
8 bits are added in synchronization with the pixel clock PC as shown in FIG. 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. , the average value of the added data, that is, the signal ALS of the top eight hits, is manually input to the subtracter 7.

Here, the pixel state of the line sensor 1 is as shown in FIG. 5, and if the latch circuit 5 reads only 8 pixels from the beginning of one line, the blind pixel 8
Output data for several pixels of G can be read and added, and the latch circuit 6 outputs the average value ALS for 8 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 1 is inputted to the subtracter 7 via the A/D converter 3, and the average value ALS is subtracted from the read signal R5 to correct the dark current. This will be applied as the image reading signal PR.

However, in the above method, if a measurement error occurs due to noise, it will be visually marked as streaks in the sub-scanning direction.

This invention was made due to the circumstances mentioned above,
The purpose of this invention is to accurately obtain the @current value using the average value of multiple pixels of the blind pixels every time multiple lines of the line sensor are read, and always based on the several lines before and after the image signal of each line. An object of the present invention is to provide a method for correcting an image reading signal, which allows accurate correction.

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 finding an average value when reading a plurality of lines of blind pixels, and using the average value to calculate and output a reading signal of the image.

(Function) As shown in FIG. 5, the line sensor 1 made of a CCD, etc. has blind pixels BC that do not have a sensor function by several pixels (for example, 155 pixels) from both ends, and has blind pixels BC that do not have a sensor function by several pixels toward the inside. (For example, it has a dummy pixel DC area with a 155-pixel light blocking mask IA arranged on its surface, and the other central part is a reading pixel RP. Normally, the reading pixel RP reads the image, It outputs an image reading signal corresponding to the amount of received light.

Conventionally, the dark current was measured using a dummy pixel DC arranged on the surface of the mask l^, and this dark current was used to correct the read signal, but in the present invention, the line sensor 1 The signal of the blind pixel BG, which is provided at both ends and does not have a sensor function, is used as a signal for dark current correction, and the average value of the blind pixels of multiple lines is used, and this average value data is used to determine the reading pixel RP. The image reading signal from the camera is corrected and output.

Since the pressure of the blind pixel BG is a signal in a state where light is completely blocked and is an average value of multiple lines, it is possible to accurately correct image reading and eliminate streaks in the sub-scanning direction when reproducing images. It does not occur.

(Embodiment) In the present invention, an average value is obtained when a plurality of lines of a plurality of blind pixels are read, and an image reading signal is corrected and output using this average value. For example, as shown in Figure 2, the output of the nth line is the output of the previous two lines (n-1, n-2).
), the average value of the blind pixels BG for five lines (n+1°0÷2), and the current line (n), to correct the image reading signal.

FIG. 1 shows an embodiment of an apparatus for implementing the method of the present invention, corresponding to FIG. 3, and this example shows a case where the average value of 8 pixels for each line of 5 lines is used. A/
The digital signal R5 (8 bits) output from the D converter 3 is input to the shift register 10, and is also manually input to one of the line memories 11-13 in synchronization with the timing signal TS. The shift register 10 outputs the data of the blind pixel BG five lines before based on the timing signal SRC from the timing generation circuit 8, and subtracts it from the current blind pixel output R5 by the subtracter 14. This subtracted value is inputted to the adder 15, and then inputted to the latch circuit 16 as the addition signal AS (4 bits). Then, the integrated clock GPC from the timing generation circuit 8
Accordingly, the latch circuit 16 adds the number of blind pixels BC, and the average value ALS (upper 8 bits) of the added data LS (chibits) is held in the latch circuit 17 at the next stage. The output signal PR is corrected by subtracting this average value ALS from the pixel signals read from the line memories 11 to 13 in the subtracter 7. As a result, the average value A of the blind pixels BC of 5 lines before and after including the target line
The line memories 11 to 13 are for three lines, and the read/write is sequentially controlled by the timing signal TS from the timing generation circuit 8. It has become.

Note that the number of pixels for calculating the average value of blind pixels may be arbitrary, and in the above explanation, a line sensor was used as an example of the solid-state image sensor, but in principle, it is also applicable to an area sensor.

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 for a plurality of lines is determined for each line read by the line sensor, and the read signal of the line is calculated using this average value. Since the correction is made, l
The dark current can be accurately determined according to the reading condition without being affected by measurement errors due to variations in each line pixel or noise, and accurate correction can be performed even in response to changes in environmental temperature, etc. It becomes possible to do it. Furthermore, even if a measurement error occurs in the blind pixel output of a certain line due to noise, the influence can be minimized and streaks can be prevented from occurring.

FIG. 5 is a timing chart showing an example of the operation, and FIG. 5 is a diagram showing an example of the pixel arrangement of the line sensor.

1... Line sensor, 2... Amplifier, 3... A/
D converter, 4.15... Adder, 5, 6, 16.17
...Latch circuit, 7゜I4...Subtractor, 8...Timing generation circuit, 10...Shift register, 11~
13...Line memory.

Claims (1)

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