JPS6163160A - Picture signal reading device - Google Patents

Abstract

PURPOSE:To converge to a specified gain in a short time by finding the difference between a value obtained by shading correcting a part that becomes a standard of white level of an original and data corresponding to correct white level, and changing rates of variation of the gain according to magnitude of the difference. CONSTITUTION:An image of light from an illuminating light source 2 reflected by a white reference plate 1 is formed on a CCD image sensor 4 by a lens 3, photoelectrically converted by the sensor 4 and amplified by an amplifier 5. An output of this amplifier 5 is converted to digital data for each picture element by an A/D converter 6, converted to a coefficient of correction by a ROM, and stored in a RAM 9. Then, 1 line of a part that becomes standard of white level in the original is photoelectrically converted by the sensor 4 and the picture signal is amplified by an initial gain and A/D-converted. The rate of variation of gain is determined for each picture element of the picture signal. When adjustment of gain is started, adjusting is made quickly by making the rate of variation of the gain large, and as target gain draws near, the rate of variation of the gain is made small, and the stability of the gain is heightened. The original is read under this optimum condition, and shading distortion is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image signal reading device used in a reading section of a facsimile machine or the like.

Configuration of the conventional example and its problems As shown in FIG. 13
, gain control voltage generation circuit 11, analog-digital converter 6, digital-digital multiplier, correction coefficient ROM 8.1 line of RAM 9, and white reference plate 1
The analog-to-digital converter 6, the digital-to-digital multiplier 7, the correction coefficient ROMs 5 and 1
A shading distortion correction device is configured by the RAM 9 for lines.

The operation of this reading section is performed as follows. First, the light reflected from the illumination light source 2 by the white reference plate 1 is imaged by the lens 3, photoelectrically converted by the COD image sensor 4, and the signal amplified by the amplifier 5 is sent to the peak hold circuit 12.
The comparator 13 compares that value with the set value, and the gain control voltage generation circuit 11 lowers the gain if the ratio is large, and increases the gain if it is small. make it work. In this way, the peak level of the signal on the white reference plane is constantly maintained at the 7I scale level of the analog-to-digital converter 6, and the signal of After data conversion, it is written to one line of RAM 9 at the specified address. Here, the correction coefficient RO
The role of M is to always make the input image signal within the shading distortion correction range a constant output image signal, that is, v
inx;1=v0°t (constant). Here, V. is an input image signal, vout is an output image signal, N is a quantization number, and M is a correction coefficient, for example, V-factor. =sV, VOut==2.
5v (constant), N=8 bits, M is 128 (
80), 6, and this value is written to 1 line/RAM 9 at the address designated by the input image signal 6V. Thereafter, data for 1 rai/min is written by similar calculations.

Next, the reference portion of the white level of the original is photoelectrically converted using the same method, and the peak hold circuit 12, comparator 13,
The gain control voltage generation circuit 11 and the amplifier 5 perform the same processing as described in ml to match the peak level of the reference value of the white imprint of the original to the full scale level of the analog-to-digital converter 6, and then The gain of amplifier 5 is fixed.

Next, the original is read, amplified by an amplifier 5 with a gain determined in the above processing, and then transferred to an analog-to-initial converter 6.
At the same time, the data written to the I'tAM 9 of 1 rai/in which the correction coefficient has been written by the above processing is quantized and input to the digital-digital multiplier 7. A digital image signal is obtained in which the level fluctuation and shading distortion of the original signal are corrected.

In the reading section of this facsimile machine, the white V/<
) The rate of gain change when adjusting the peak level of the reference portion of V to the full scale of the analog-to-digital converter is set to a low value so that the level changes little by little over the scanning time of one line. There is. Therefore, the time it takes to reset the gain according to the document's white level standard must be at least several tens of lines, taking into consideration cases where the difference from the previous value is large. In addition, there are inconveniences such as having to stop the document at a portion that serves as a reference for the white level.

This problem can be solved by increasing the rate of change of the gain so that the peak level of the reference portion of the white level of the document approaches the full scale level of the analog-to-digital converter in a short period of time. but,
In that case, the problem arises that the gain is not stable and may deviate from the correct gain value depending on the timing at which the gain is fixed.

Purpose of the Invention The present invention solves the above-mentioned conventional problems and provides an image signal that can converge to a predetermined gain in a short time without the gain becoming unstable when automatically adjusting the gain of an original. This was done for the purpose of providing a reading device.

Structure of the Invention The present invention corrects the shading of a portion of the document that serves as a reference for the white level, and uses the difference between the digital data obtained as a result and the digital data corresponding to the correct white level to correct the gain when the difference is large. Increase the rate of change of
On the other hand, when the rate of change is small, the above objective is achieved by making the rate of change small. That is, the image signal reading device of the present invention includes a shading correction means for correcting shading distortion by scanning a white reference plate before scanning information on a document, and 4r; Before scanning 5, a portion of the original that serves as a reference for the white level is scanned and the shading distortion correction is performed by the shading correction means, and the first value obtained as a result is compared with a predetermined correct white level. A rate of change selection means detects a difference from a reference and selects a rate of change in the gain according to the difference, and a gain of the original is inputted to the shading correction means according to the rate of change selected by the rate of change selection means. It has a gain variable means for increasing and decreasing the gain.

DESCRIPTION OF EMBODIMENTS Hereinafter, details of the structure of the present invention will be explained based on embodiments shown in the drawings.

FIG. 2 is a block diagram showing a schematic configuration of an embodiment of a reading section of a facsimile machine according to the present invention, in which parts denoted by the same reference numerals as those in FIG. 1 are the same parts. It is. That is, 1 is a white reference plate, 2 is an illumination light source,
3 is a lens, 4 is a COD image sensor, and 5 is a gain variable means whose gain can be changed by a control voltage, that is, an amplifier. 10 is a means for correcting shading distortion, and its correction circuit includes an analog-digital converter 6, a multiplier 7, a correction coefficient ROM 5, and an R for one line.
It consists of AM9. 14 is a change rate selection means that uniquely determines the change rate of the output voltage according to the input digital value, that is, a variable gain control voltage generation circuit;
6 indicates a digital input signal, and 17 indicates a gain control voltage output signal.

Figure 3 shows the variable gain/control voltage generation circuit 1 in Figure 2 above.
FIG. 4 is a circuit diagram showing an example of No. 4; In the figure, 12 is a decoder that converts a 4-bit digital signal into 16 signals, and each decoded signal turns ON10.
Analog switches 81 to S16 that perform FF are connected at one end to each terminal of the resistors R1 to R8, and at the other end to the power supply or ground. Control voltage output 1γ
One of the terminals of capacitor G is connected to G, and the other terminal is connected to ground.

Next, the operation of this embodiment will be explained. First, as a first operation, a shading distortion correction coefficient is written into the RAM 9 as a reference value. In this first operation, the light reflected from the illumination light source 2 by the white reference plate 1 is imaged on the CCD image sensor 4 by the lens 3, photoelectrically converted by the COD image sensor 4, and then transferred to the amplifier 5. amplify by. At this time, the gain of the amplifier 5 is
After the white level output value is amplified, it is fixed at a value that satisfies the input level condition of the analog-to-digital converter 6. The amplified signal is converted into digital μm data by an analog-to-digital converter for each pixel, and then converted into a correction coefficient by a correction coefficient ROM 5. The relationship between the digital input data and the correction coefficient data at this time is Vinx7: K Here, V. is the digital input value of the white reference plate, N is the correction coefficient data, N is the number of bits, and K is the corrected data of the white reference plate and is a constant value. Now, if we use an 8-bit analog-to-deinterlacer converter and set the input full scale to 5V, the value of the white reference plate of 2.5V is V. =8
Q16 (128,.) to a constant value: 80.6 (12
8, o), then M = 10016 (2661o), and this value is the 1 line RA of the specified address of the input image signal.
Caught in M9.

Next, as a second operation, one line of the white level reference portion of the document is photoelectrically converted by the COD image sensor 4 in the same manner, and the image signal is amplified by the amplifier 5 at an initial gain. The image signal is converted pixel by pixel into digital data by an analog-to-digital converter 6. The data and the value read from the address corresponding to each pixel in the RAM 9 are used in the multiplier 7 to perform the calculation shown in the following equation.

vout ” vin Assuming that the value is larger than the board data 8016 (1281o), and V = BO,, (176, .), the corrected output vout ” Bo+b (17610)
Therefore, the signal level of the white reference plate is 30,6 (48,
. ) You can see that it is large.

This V. Of the data of ut, the upper 4 bits are input to the variable gain control voltage generation circuit 14, decoded, and
One of the six analog switches 81 to S16 is selected, and as a result, whether to charge or discharge the capacitor C1 and the time constants T20 and R at that time are determined. C is the capacitance of the capacitor C4, and R is the combined resistance value of the resistors formed by the selected switches. The relationship between the upper 4 bits of the vout data, the selected analog switch, the charging/discharging of the capacitor, and the time constant is shown in the table below. That is, vout of the corrected output value of the white reference plate =
As the difference from s 0.6 becomes smaller, the time constant becomes larger and the voltage change rate of the control voltage output 17 becomes smaller. This voltage uniquely determines the gain of the amplifier 5. The rate of change becomes smaller. Conversely, the larger the difference from vout = s 0.6, the larger the rate of change in gain.

(Margin below) In this way, the rate of change in gain is determined for each pixel of the image signal of one line of the part that serves as the reference for the white level of the original, and when gain adjustment starts, the rate of change in gain is much faster. Adjustment is performed, and as the gain gradually approaches the target gain, the rate of change in the gain becomes smaller, increasing the stability of the gain. When the gain stabilizes to the target value, gain hold signal 1
6 to ON, analog switches 81 to S, and all 6 to O.
The control voltage is held as an FF, and as a result, the gain is fixed.

In this optimum gain state, as a third operation, the original is read and amplified using the same method, and shading distortion correction is performed using the method described above.

゛ Effects of the Invention As is clear from the above explanation, according to the present invention, when the difference between the auto gain control gain and the correct gain is large, the gain change rate is large, and when the difference is small, the gain change rate is small. Since the ratio becomes small, it is possible to perform automatic gain control in which the time it takes for the gain to converge to the correct target value is short and the gain is stable at the time of convergence. Therefore, it has the remarkable effect of shortening the gain adjustment time that occurs when reading a document in a facsimile machine.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the structure of a reading section of a conventional facsimile machine, FIG. 2 is a block diagram showing the structure of an embodiment of the reading section of a facsimile machine according to the present invention, and FIG. 3 is a block diagram showing the structure of a reading section of a facsimile machine according to the present invention. FIG. 1 is a circuit diagram showing an example of a circuit. 1...White reference plate, 2...Illumination light source, 3
... Lens, 4 ... COD image sensor, 5 ... Amplifier (gain variable means), 6.
...Analog-digital/' converter, 7...
Yu-Digita! Radial digital multiplier, 8...Correction coefficient ROM, 9...RAM, 10...
・Shading correction means, 11...Gain control voltage generation circuit (change rate selection means), 12...
Peak hold circuit, 13...Comparator, 14.
...Variable gain control voltage generation circuit, 15...
...gain hold signal, 16...digital input signal, 1 completion...gain control voltage output signal,
S1~S16... Analog switch, R1-
R8...Resistor, C4...Capacitor.

Claims (1)

[Claims] shading correction means for correcting shading distortion by scanning a white reference plate before scanning information on a document; and shading correction means for scanning a portion of the document serving as a white level reference before scanning the document. A change rate that performs shading distortion correction, detects a difference between a first value obtained as a result of the shading distortion correction and a reference value for a predetermined correct white level, and determines a gain change rate according to the difference. An image signal reading device comprising: a selection means; and a gain variable means for increasing or decreasing the gain of the document input to the shading correction means according to the change rate selected by the change rate selection means.