JPH04160870A - Output level correction device for image sensor - Google Patents

Abstract

PURPOSE:To attain reproduction of a picture with fidelity and expression of intermediate tone by reading a correction data of a relevant picture element from a memory synchronously with the scanning of an image sensor at read scanning and adding and subtracting a picture signal output of the image sensor and the correction data. CONSTITUTION:The image sensor 30 is provided with a memory 33 storing in advance a correction data corresponding to deviation from a black level for each picture element of one line when the image sensor 30 reads and scans an original of all black levels, a timing control means 32 to read a correction data of a relevant picture element from the memory 33 synchronously with the scanning of the image sensor 30 at read and scanning, and a correction means 35 to eliminate deviation from a black level by adding or subtracting the picture signal output of the image sensor 30 and the correction data. Then the deviation from a black level due to a stray light caused mechanically or optically is eliminated by electric processing corresponding to each picture element on one line and a proper picture signal without deviation from a black level is obtained. Thus, reproduction of a picture with fidelity and expression of intermediate tone are attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an output level correction device for an image sensor used in facsimiles and the like.

Conventional technology Figure 2 shows a CCD using a reduction optical system, which has been widely used in the past.
A waveform diagram showing the output voltage level of the image sensor.
a indicates the image signal level when an all-white original is read, and b indicates an image signal level when an all-black original is read. Ideally, the image signal level b when reading an all-black original is Ov, but in addition to the reflected light from the original, stray light enters the image sensor due to various mechanical and optical reasons. , some output is produced as shown in the figure. This is the so-called black level floating. This black level floating has a particularly large effect on the reproduction of halftone image defects.

Figure 3 is a waveform diagram showing the output voltage level of the image sensor when reading a grayscale original (several gray colors with different densities arranged so that the difference in density is visually evenly spaced). However, in the actual output, compared to the ideal waveform C (solid line) in which the black level does not float, the black level floats by about 20- as shown by the minimum voltage level C of the waveform d (broken line). In order to suppress such floating black levels and reproduce originals containing halftones with high image quality, electrical processing less than conventional methods has been applied.

FIG. 4 is a schematic block diagram showing a conventional image sensor output level correction device. 1 is an image sensor, 2 is a differential amplifier, 3 is a potentiometer for obtaining an arbitrary DC voltage, and 4 is a facsimile side This is an image processing circuit.

The output f of the image sensor 9-1 is an analog image signal including a floating black level, and is input to the differential amplifier 2. Since the voltage corresponding to the floating black level (Fig. 4 e) is applied from the potentiometer 3 to the other input terminal of the differential amplifier 2, the output g has an ideal waveform with no apparent heat level floating. The signal is then input to the image signal processing circuit 4 on the facsimile side.

Conventional image sensor level correction devices subtract the voltage corresponding to the black level floating from the output of the image sensor, thereby obtaining image information without apparent heat level floating and producing good halftone originals. I realized the reproduction of .

Problems to be Solved by the Invention However, although the conventional image sensor output level correction device is capable of sufficient correction when the black level float is constant over one line, in reality The black level drop in the image is not necessarily constant. Furthermore,
In the so-called contact image sensor of the same-magnification imaging type that has been widely used in recent years, the black level deviation in one line varies considerably, so the conventional technology has a problem in that the reproducibility of halftone originals is poor.

The reason why black level variation is not constant within the width of one line in a contact image sensor will be explained below.

FIG. 5 is a schematic cross-sectional view of a reading section of a contact image sensor using a CdS photoelectric conversion element. A support lath 11 is placed on a base 10 that integrates the whole, and a sensor glass 12 and a spacer are placed on the support glass 11 on a lath 13.
is located.

A light-shielding layer 15 is provided on the sensor glass 12 to regulate incident light from the LED array 14. On the light-shielding layer 15, Cd8 photoelectric conversion elements 16 are arranged at a density of 8 pieces/h in the main scanning direction. are arranged in

A window 17 for entry is provided in a pair with the CdS photoelectric conversion element 16. Further, a thin plate glass 18 is bonded thereon as an abrasion resistant layer using a UV adhesive resin 19. The original 20 is conveyed over the thin glass 18 while being pressed by a platen roller 21 .

The light that enters the CdS photoelectric conversion element 16 from the LED array 14 is mainly that shown by the solid line L1, and if there is no other incident light, the Cd8 photoelectric conversion element 16 will output an appropriate output according to the density of the original. can get. However, in reality, the light that enters after being reflected on the base 2 (broken @L2), the light that enters from between the sensor glass 12 and the spacer glass 13 (
broken line L3), light that leaks through the light shielding layer 15 and enters (broken line L4), and light that enters from the outside (broken line L5).
There are stray lights such as these, and it is impossible to completely eliminate them.

Since the image sensor has a large-area, same-magnification structure, the intensity of these stray lights is affected by variations in mechanical accuracy (for example, non-linearity of the LED array, bending of the base, cutting condition of the glass, etc.). It can be said that it cannot be uniform at each position in the main scanning direction.

The present invention has been made in view of the above-mentioned problems, and is an image sensor output level correction that enables obtaining an appropriate image signal without black level floating, and enables highly faithful image reproduction and halftone expression. The purpose is to provide equipment.

Means for Solving the Problems In order to achieve the above-mentioned objects, the present invention provides an image sensor and a correction corresponding to the black level deviation of each pixel in one line when the image sensor reads and scans an all-black original. a memory for storing data in advance; a timing control means for reading correction data of a corresponding pixel from the memory in synchronization with the scanning of the image centimeter during reading scanning; and adding the image signal output of the image sensor and the correction data. or a correction means for removing black level floating by performing subtraction.

Operation Since the present invention has the above-described configuration, the floating black level caused by stray light generated mechanically and optically is removed by electrical processing for each pixel on one line, and the black level is removed by electrical processing corresponding to each pixel on one line. As a result of being able to obtain an appropriate image signal without level floating, more faithful image reproduction and halftone expression are possible.

Embodiment FIG. 1 shows a schematic configuration of an image sensor output level correction apparatus according to an embodiment of the present invention.

In the figure, 30 is a contact image sensor, 31 is an address counter, and these operate under the timing control of a timing circuit 32. A memory (ROM) 33 stores correction data corresponding to each pixel of the photoelectric conversion elements arranged in the main scanning direction of the contact image sensor f30. This correction data is written in advance in the manufacturing process by scanning an all-black document for each image sensor and checking the black level deviation for each digital conversion element. Furthermore, 34 is a digital/analog converter (D/A converter), 35 is a differential amplifier, and 36 is an image signal processing circuit on the facsimile side, which includes a sintering circuit, a halftone processing circuit, and the like.

This device configured as described above operates as follows.

First, the contact image sensor 30 and address counter 3
1 is shuffled by the start pulse S1 from the timing circuit 32 and becomes ready to start reading scan. Next, scanning is started, and the contact image sensor 30
sequentially scans one line pixel by pixel. At the same time, the address counter 31 also counts the clock pulse S2 and sequentially outputs the counted value to the memory 33. The output of the address counter 31 is an address input port of the memory 33, and the memory 33 reads out the correction data stored at the designated address corresponding to each pixel of the output of the contact image sensor 30.

The output of the memory 33 is converted into an analog signal by a D/A converter 34 at the next stage, and is input to a differential amplifier 35 in synchronization with the image signal output of the contact image sensor f30 for each pixel. The differential amplifier 35 connects the image signal output of the contact image sensor 30 and D
/A converter 34 output black level float signal, and 1
Since the image signal is amplified and outputted, the image signal outputted to the image signal processing circuit 36 including a binarization circuit etc. becomes an appropriate signal with black level floating removed.

Effects of the Invention As is clear from the above description, the present invention provides an image sensor and correction data corresponding to the black level deviation for each pixel in one line when the image sensor reads and scans an all-black original. a memory for storing, a timing control means for reading correction data of a corresponding pixel from the memory in synchronization with the scanning of the image sensor during reading scanning, and adding or subtracting the image signal output of the image sensor and the correction data. The device is equipped with a correction means for removing black level floating by performing a mechanical adjustment, and electrically corrects the black level floating caused by optically generated stray light for each pixel on one line. As a result of the processing, it is possible to obtain an appropriate image signal with no floating black level, and as a result, it is possible to reproduce an image with high fidelity and to express halftones.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an image sensor output level correction device according to an embodiment of the present invention, FIGS. 2 and 3 are signal waveform diagrams showing the output level of an image sensor according to a conventional device, and FIG. 4 is a conventional image sensor output level correction device. FIG. 5 is a schematic block diagram of an output level correction device for an image sensor, and FIG. 5 is a schematic sectional view of a reading section of a contact image sensor using a CdS light conversion element. 30... Contact image sensor, 31... Address counter, 32... Timing circuit, 33... Memory, 34... D/A converter, 35... Differential amplifier. Name of agent: Patent attorney Akira Okaji and 2 others
Figure 6 Figure 4

Claims (1)

[Claims] an image sensor, a memory that stores in advance correction data corresponding to black level deviation for each pixel of one line when this image sensor reads and scans an all-black original, and a memory that is synchronized with the scanning of the image sensor during reading and scanning. an image comprising: timing control means for reading out correction data of the corresponding pixel from the memory; and correction means for removing black level floating by adding or subtracting the image signal output of the image sensor and the correction data. Sensor output level correction device.