JPH0545110B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] In a sizing correction method that corrects the non-uniformity of the light source between the center and the periphery of a reading area by controlling the gain of an image signal, the white level in the center is adjusted to a predetermined value. A sizing correction method is provided in which gain data is obtained to match the voltage, and this is set as the initial value of the gain to correct the offset.

[Industrial application field]

The present invention relates to an improvement in a sagging correction method in a facsimile machine or the like.

In reading devices such as facsimile machines, a fluorescent lamp is used as a light source, and a sagging correction means is provided to correct sagging of the image signal due to uneven illuminance between the center and peripheral areas of the reading area. It is being

As a method of shading correction, a white plate is irradiated in advance, the white level in the center is amplified to a predetermined voltage, and the difference between the predetermined voltage value and the white level in the reading area is detected to adjust the gain of the automatic gain control section. However, if the white level decreases due to aging of the fluorescent lamp, etc., and an offset from the specified voltage value occurs, a correction delay will occur and readjustment will be required. There is a problem.

Therefore, there is a need for a sagging correction method that does not require the above-mentioned readjustment.

[Conventional technology]

FIG. 5 is a block diagram of a conventional sagging correction section in a facsimile machine, FIG. 6 is an explanatory diagram of a sagging correction method, and FIG. 7 is an explanatory diagram of correction delay due to offset.

FIG. 5 shows the main parts of the reading section of the facsimile apparatus, in which 1 is a fluorescent lamp, 2 is a light shielding plate, 5 is a sensor CCD, 6 is an amplifier, and 7 is a saging correction section.

In the above configuration, the document 3 sub-scanned along the white board 4 is illuminated by the fluorescent lamp 1, and its image is
Accumulated in CCD5.

This CCD 5 is read out in the line direction by a read clock CLK and amplified by an amplifier 6 to a predetermined level.

Here, the fluorescent lamp 1 is used for reading scanning (line direction).
However, since the length is finite, there is a difference in illuminance between the center and the periphery of the document 3.
Shading occurs in the image signal.

This shading can be corrected by gain control to keep the white level constant within the reading area, and one example of this will be explained below.

A light shielding plate 2 is arranged in front of the fluorescent lamp 1, and the illuminance is corrected so that the illuminance at the center of the reading area and at a predetermined position on the periphery (a position larger than the maximum document width) is the same [Fig. 6-] be done.

When the white board 4 is irradiated with this corrected light source and the area between the predetermined positions is read, the gain is controlled by the amplifier 6 so that the image signal (white level) at the center of the white board 4 becomes a predetermined voltage A (V). An amplifier output as shown in FIG. 6 is obtained.

With this amplifier output, correction data 51 for the initial value of gain is stored in the memory 13 so that the output of the automatic gain control section 8 is kept constant, and the automatic gain control section 8 is controlled to gain based on this correction data 51 when reading a document. to correct the image signal.

The details of the sagging correction will be explained below.

In the sizing correction section 7, 8 is an automatic gain control section whose center gain is approximately 1, and 9 is a comparator that compares the output voltage of the AGC 8 with a reference voltage A (V), in which the output voltage of the AGC 8> The correction data 51 is "1" when A, and "0" when the output voltage of AGC8<A.

11 is a saging counter (SD counter) composed of an up-down counter; 12 is a D/A converter that converts the output data of the saging counter 11 into an analog voltage;
A gain control signal 53 is output to the AGC 8.

13 is correction data 51 output from the comparator 9.
The memory that stores , is .

With the above configuration, the following correction operation is performed.

(1) Adjuster so that the central output of the white board 4 in the amplifier 6 becomes a predetermined voltage (reference voltage A volt)
Adjust the gain using VR.

(2) At the start of the correction operation, the saging counter 11
Initial value data 50 is set in advance so that the white level at a predetermined position on the periphery (or in the center), which is the correction start position, becomes a predetermined voltage A at the output of the AGC 8, and is used as a gain control signal 53.
Output to AGC8.

(2) When the white board 4 is read, voltages as shown in FIG. 6 are sequentially input to the AGC 8;
The output of the AGC 8 is compared with the reference voltage A, and correction data 51 representing the magnitude is output.

(3) The saging counter 11 is clocked based on the [“1”, “0”] data of this correction data 51.
CLK is counted up or down to correct the initial value data 50, and the result is output to the D/A converter 12 (FIG. 6-) to control the gain of the next pixel.

(4) If the above operation is performed for each clock CLK used for line scanning and reading, and the gain control width of AGC8 and the white level change width are approximately the same, then
The white level output of the AGC 8 is corrected to be substantially flat as shown in FIG.

(5) In the above process, the correction data 51 is the address counter 1 that counts the clock CLK.
4 is stored in the memory 13.

(6) When reading a document, the switching unit 10 is switched, the correction data 51 in the memory 13 is output to the sizing counter 11, and the gain of the AGC 8 is controlled in accordance with the reading position.

[Problem that the invention seeks to solve]

In the conventional saging correction method described above, fixed initial value data 50 is given as the initial value of the gain of the automatic gain control section, that is, the initial value of the saging counter 11.

Therefore, when the fluorescent lamp, CCD, amplifier, etc. change over time and the white level decreases, an offset occurs between the white level and the reference voltage at the time when the sizing correction is started (at a predetermined position in the periphery).

For this reason, if the gain control width for each pixel is smaller than the offset, as shown in Figure 7, offset correction requires multiple pixels, causing a correction delay, and the amplifier gain must be readjusted. The problem arises that this is not the case.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a sagging correction method that does not require offset adjustment due to aging or the like.

[Means for solving problems]

For the above purpose, the sagging correction method of the present invention compares the white level at the center with a predetermined voltage A, as shown in FIG. An initial value data setting section 15 is provided to acquire gain data 52 to match the voltage A of , and to set the gain data 52 in the sizing correction section 7 as the initial value data 50 of the automatic gain control section 8 .

[Effect]

Prior to the shading correction, the white board is read to obtain gain data 52 that makes the output voltage at the center match a predetermined voltage value (reference voltage) A, and is set as initial value data 50 of the automatic gain control section 8.

Since the illuminance at the predetermined position in the periphery where the shading correction starts and the central part are corrected to be the same,
If the acquired gain data 52 is the initial value data 50, the white level at the predetermined position matches the reference voltage,
Offset is eliminated.

〔Example〕

Embodiments of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 2 is an explanatory diagram of the operation, FIG. 3 is a block diagram of the sagging correction section of the embodiment, and FIG. 4 is an explanatory diagram of the sagging correction procedure of the embodiment.

In the initial value data setting section 15 shown in FIG. 3, 16 is an offset counter composed of an up-down counter, 17 is a comparator for comparing the reference voltage A (volt V) and the output voltage of the AGC 8, If the output of AGC8 is <A, it is "1"; if the output of AGC8 is >A, it is "0"; the up-down control data 54 is output.

Reference numeral 18 denotes a setting control section, which sets the gain data setting area, controls the output of the offset counter 16 to the D/A converter 12 through the saging counter 11 during the acquisition operation, and controls the output of the offset counter 16 during the saging correction. Preset the counter 11.

The same reference numerals represent the same objects throughout all other figures.

The operation of setting the initial value to the automatic gain control unit AGC8 will be explained below. Refer to FIGS. 2 and 4 (1) Prior to reading the original, the white board 4 is irradiated.

(2) The first line (FIG. 4) is read, and the setting control section 18 counts the read clock CLK.

When the predetermined setting area (center) is reached, the up-down control data 54 output by the comparator 17
Based on the offset counter 16, the clock
Count up (or down) CLK.

The value of the offset counter 16 is outputted to the A/D converter 12 via the sizing counter 11, and increases (or decreases) the gain of the AGC 8.

(3) The next pixel based on the set gain is compared with the reference voltage A, and the gain is further controlled, and after matching with the reference voltage A (V), it is balanced.

(4) After the reading of one line is completed, the gain data 52 counted by the offset counter 16 is transferred to the saging counter 11 as the initial value data 50.
The conventional sagging correction operation described above is performed in the next white board reading line (FIG. 4).

Although the initial value of the offset counter 16 is arbitrary, it usually counts from "0".

As described above, the difference (offset) between the reference voltage and the white level at the starting point of the sizing correction is obtained by acquiring the gain data that matches the center white level with the reference voltage and setting this as the initial value of the automatic gain control section 8. ) is corrected, and the sagging correction delay is eliminated.

〔Effect of the invention〕

Since the present invention provides a sagging correction method that includes means for detecting and eliminating offset in advance, it is extremely effective in eliminating correction delays in reading devices.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of operation, Fig. 3 is a block diagram of the sagging correction section of the embodiment, Fig. 4 is an explanatory diagram of the sagging correction procedure of the embodiment, and Fig. 5 is a block diagram of a conventional sagging correction unit in a facsimile machine, FIG. 6 is an explanatory diagram of a sagging correction method, is an explanatory diagram of correction using a light-shielding plate, is an illustration of correction in a sagging correction unit, and FIG. 7 is a diagram of correction using an offset. In the diagram, 1 is a fluorescent lamp, 2 is a light shielding plate, 3 is an original, 4 is a white board, 5 is a sensor CCD, 6 is an amplifier, 7 is a sizing correction section, and 8 is an automatic gain control section. , 9 is a comparator, 10 is a switch, 11 is a sizing counter (SD counter), 12 is a D/A converter, 13 is a memory, 14 is an address counter, 15 is an initial value data setting unit, 16 is an offset 17 is a comparator, 18 is a setting control unit, 50 is gain initial value data, 51 is correction data, 52 is gain data,
53 is a gain control signal, 54 is up-down control data, and A is a reference voltage (predetermined voltage).

Claims (1)

[Claims] 1. A light-shielding plate 2 that matches the illuminance at a predetermined position in the central part of the reading area and a predetermined position on the periphery of the reading area, and an automatic gain control section 8, which sets the gain at the predetermined position to predetermined initial value data 50. correction data 51 for the initial value data 50 based on the difference between a predetermined voltage value A corresponding to the white level of the predetermined position and the white level of the reading area;
In a reading device equipped with a sizing correction unit 7 that acquires a value corresponding to a reading position and controls the gain of an image signal, the white level of the central portion is compared with the predetermined voltage A, and the white level of the central portion is An initial value data setting unit 15 is provided to acquire gain data 52 that makes the level match the predetermined voltage A, and to set the gain data 52 in the sizing correction unit 7 as the initial value data 50. A sagging correction method characterized in that sagging correction is performed by correcting an offset between the white level and the predetermined voltage A.