JPS63200676A - Shading correction system - Google Patents

Abstract

PURPOSE:To eliminate the need for offset adjustment due to secular change by acquiring a gain data making a white level at midposition coincident with a prescribed voltage and setting it to the gain initial value so as to correct the offset. CONSTITUTION:The white level at the middle part and a prescribed voltage A are compared and the white level of the middle part is made coincident with a prescribed voltage A by a gain data 52 and the gain data 52 is set to the shading correction section 7 as an initial data 50 of an automatic gain control section 8 by an initial data setting section 15. Prior to the shading correction, a white board is read and the gain data 52 making the output voltage of the middle part coincident with a prescribed voltage (reference voltage) A is acquired and set as the initial data 50 of the automatic gain control section 8. Thus, the illuminance of the prescribed position at the peripheral position starting the shading correction and the middle part is corrected identically, then using the acquired gain data 52 as the initial data 50, the white level of the prescribed position is made coincident with the reference voltage and the offset is eliminated.

Description

[Detailed Description of the Invention] [Summary] In a shading 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 matched to a predetermined voltage. A shading correction method is provided that acquires gain data that causes an increase in gain, sets this as an initial value of gain, and corrects offset.

[Industrial application field]

The present invention relates to improvements in shading correction methods for facsimile machines and the like.

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

As a shading correction method, 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 and the gain of the automatic gain control section is adjusted. Although a method of controlling has been adopted,
If the white level decreases due to aging of the fluorescent lamp or the like and an offset occurs between it and a predetermined voltage value, there is a problem that a correction delay occurs and readjustment is required.

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

[Conventional technology]

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

Figure 5 shows the main parts of the reading section of a facsimile machine, where 1 is a fluorescent lamp, 2 is a light shielding plate, 5 is a sensor CCD, and 6 is a light shielding plate.
is an amplifier, and 7 is a shading correction section.

In the above configuration, the original 3 is sub-scanned along the white board 4.
is irradiated by the fluorescent lamp 1, and its image is stored on the CCD 5.

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

Here, the fluorescent lamp 1 is arranged in the reading scanning (line direction) direction, but since its length is finite, there is a difference in illuminance between the center and peripheral parts of the document 3, causing shading in the image signal. Occur.

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

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

When the white board 4 is irradiated with this corrected light source and the area between the predetermined positions is read, an image signal (white level) at the center of the white board 4 is obtained.
By the amplifier 6 whose gain is controlled so that the voltage 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 the gain is stored in the memory 13 so that the output of the automatic gain control section 8 is kept constant.
1, the automatic gain control unit 8 is gain controlled to correct the image signal.

The details of the above shading correction will be explained below.

In the shading correction section 7, 8 is an automatic gain control section whose center gain is approximately l, and 9 is an AG
This is a comparator that compares the output voltage of C8 and a reference voltage A (V), and outputs correction data 51 which is "1" when the output voltage of AGC8>A and 0 when the output voltage of AGC8 is less than A.

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

A memory 13 stores the correction data 51 output from the comparator 9.

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

(11 Adjust the gain with the regulator R so that the output from the center of the white board 4 in the amplifier 6 becomes a predetermined voltage (reference voltage A volt).

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

(2) When the white board 4 is read, the voltages shown in FIG. 6 (If)-0 are sequentially input to the ACCB, but the comparator 9 compares the output of the AGC 8 with the reference voltage A, and generates correction data representing the magnitude. 51 is output.

(3) The shading counter 11 uses the clock CLK based on the [1”, “0”] data of the correction data 51.
The initial value data 50 is corrected by amplifying or down-counting, and the result is output to the D/A converter 12 (see Fig. 6).
It)-■) 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 AGC 8 and the width of change in white level are approximately the same, the white level output of AGC 8 will be As shown in FIG. (II)-■, it is corrected to be substantially flat.

(5) In the above process, the correction data 51 is stored in the memory 13 based on the address counter 14 that counts the clock CLK.

(6) When reading a document, the switching unit 10 is switched, the correction data 51 in the memory I3 is output to the shading 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 shading correction method described above, the initial value of the gain of the automatic gain control unit, that is, the shading counter 1
Fixed initial value data 50 was given as the initial value of 1.

Therefore, when the fluorescent lamp, COD, 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 shading correction is started (at a predetermined position in the peripheral area).

Therefore, if the gain control width for each pixel is smaller than the offset, as shown in Figure 7, multiple pixel bones are required for offset correction, 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 problems, it is an object of the present invention to provide a shading correction method that does not require offset adjustment due to aging or the like.

[Means for solving problems]

For the above purpose, the shading correction method of the present invention compares the white level at the center with a predetermined voltage (A) and determines the white level at the center, as shown in FIG. Gain data (5) to match the predetermined voltage (A)
2) and sets the gain data (52) in the shading correction unit (7) as the initial value data (50) of the automatic gain control unit (8).
) will be established.

[Effect]

Prior to 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 peripheral area where shading correction is started and the central area are corrected to be the same, if the acquired gain data 52 is used as the initial value data 50, the white level at the predetermined position matches the reference voltage, Offset is canceled.

〔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 shading correction section of the embodiment, and FIG. 4 is an explanatory diagram of the shading 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 that compares the reference voltage A (volt V) and the output voltage of the AGC 8, and the AC , C8 outputs the amplifier down control data 54 (“1” if A; output of AGC8; “0” if A).

Reference numeral 18 denotes a setting control section, which sets the gain data setting area, and converts the output of the offset counter 16 through the shading counter 11 to the D/A converter 1 during the acquisition operation.
2, and precents the shading counter 11 during shading correction.

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. See FIGS. 2 and 4. (1) Prior to reading the original, the white board 4 is irradiated.

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

When the predetermined setting area (center portion) is reached, the offset counter 16 counts up (or counts down) the clock CLK based on the up/down control data 54 output from the comparator 17.

The value of offset counter 16 is shading counter 1
1 to the A/D converter 12, and increases (or decreases) the gain of the AGC 8.

(3) The next pixel based on the gain set above is compared with the reference voltage A to further control the gain, and the reference voltage A (
Equilibrate after matching V).

(4) After reading one line, offset counter 1
Gain data 52 counted to 6 is initial value data 50
The above-mentioned conventional shading correction operation is performed at the next white board reading line [FIG. 4 (It)].

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

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

〔Effect of the invention〕

The present invention provides a shading correction method that includes means for detecting and eliminating offsets in advance.
The effect of eliminating the correction delay in the reading device is extremely large.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the principle of the present invention, Figure 2 is a diagram explaining the operation, Figure 3 is a block diagram of the shading correction section of the embodiment, Figure 4 is a diagram explaining the shading correction procedure of the embodiment, and Figure 5 is a facsimile. A block diagram of a conventional shading correction unit in the device. Figure 6 is an explanatory diagram of a shading correction method. (1) is an illustration of correction using a light shielding plate, (II) is an illustration of correction in the shading correction unit, and Figure 7 is an illustration of a correction method using an offset. FIG. 4 is a correction delay explanatory diagram. In the figure, 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 shading correction section, 8 is an automatic gain control section, 9 is a comparator, 10 11 is a shading 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 counter, 17 is a comparator, 18 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; A is a reference voltage (predetermined voltage).

Claims (1)

[Scope of Claims] 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, and an automatic gain control unit (8), which sets the gain at the predetermined position to a predetermined initial value. It is set based on the data (50), and a predetermined voltage value (A
) and a white level of the reading area, a shading correction unit that acquires correction data (51) for the initial value data (50) corresponding to the reading position and controls the gain of the image signal; Comparing the white level of the center portion with the predetermined voltage (A) and obtaining gain data (52) for making the white level of the center portion coincide with the predetermined voltage (A); , an initial value data setting section (15) that sets the gain data (52) as the initial value data (50) in the shading correction section (7);
A shading correction method comprising: providing a shading correction method, and correcting an offset between the white level at a predetermined position and the predetermined voltage (A) to perform shading correction.