JPS6149871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image signal amplitude correction device for correcting the amplitude of an image signal in response to changes in the light amount of a light source and the density of the background of a document in a facsimile transmitter or the like.

Generally, in facsimile transmitters, the amplitude of the image signal is corrected in order to eliminate the effects of the rise characteristics of a light source such as a fluorescent lamp that illuminates the original, changes in light intensity due to aging, and changes in the density of the original's background. There is a need.

FIG. 1 shows a conventional image signal amplitude correction device.
In this conventional device, an analog image signal a output from an image sensor 1 is input to an amplifier circuit 3 via a buffer 2, and is amplified by the amplifier circuit 3. The sampling interval selection circuit 4 selects a sampling interval under the control of the sampling interval selection signal S ₁ and outputs the output of the amplifier circuit 3 in the same interval to the peak hold circuit 5 .

As a result, the peak hold circuit 5 holds the peak value of the output of the amplifier circuit 3 in the sampling period, and feeds back this hold value to the gain control section of the amplifier circuit 3. As a result, the gain of the amplifier circuit 3 and, in turn, the amplitude of the output of the amplifier circuit 3 are controlled according to the hold value of the peak hold circuit 5.

Since the peak hold circuit 5 attenuates the hold value with a predetermined time constant, the hold value is determined by the amount of light from the light source, including when the peak value of the output of the amplifier circuit 3 is lower than the previous point. and is sequentially updated according to changes in the ground density of the manuscript.
Therefore, the amplitude of the output of the amplifier circuit 3 is controlled according to changes in the light intensity of the light source and the density of the background of the document, so the amplitude is corrected for changes in the light intensity of the light source and the density of the background of the document. The image signal b can be obtained from the same output.

Here, the correction accuracy will deteriorate if the time constant is not set to match the light intensity of the light source and the rate of change in the density of the background of the document, but in general, the density of the background of the document is slower than the change in the light intensity of the light source. The change in is more steep.

However, in the conventional device, since the same peak hold circuit 5 detects changes in the light intensity of the light source and changes in the density of the background of the original, the speed of change in the light intensity of the light source and the change in the density of the background of the original are detected by the same peak hold circuit 5. The time constant had to be set as a compromise between speed and speed, and the accuracy of correction for changes in the amount of light from the light source and the density of the background of the document was not sufficient.

When reproducing halftones, highly accurate correction is required, so the above-mentioned drawbacks have become particularly noticeable.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional art, and provides an image signal amplitude correction device that can highly accurately correct the amplitude of an image signal in response to changes in the light amount of a light source and the density of the background of a document. The purpose is to provide.

First, to give an overview, the present invention divides the reading scanning surface into an outside-of-document area and an inside-of-document area, and the peak value of the corrected image signal in each of these areas is transferred to an outside-of-document peak value holding circuit and an inside-of-document peak value. By controlling the amplitude of the corrected image signal using a value obtained by superimposing the peak values held in each of the peak value holding circuits, each of the peak value holding circuits can control the held value. The attenuation rate can be set independently from each other so as to be optimal for the rate of change in the light amount of the light source or the rate of change in the density of the background of the document.

The present invention will be explained in more detail below based on embodiments shown in the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention, and FIG. 3 shows a signal waveform diagram in the same embodiment. In this embodiment, it is assumed that the area outside the document on the reading scanning surface is a white background.

A subtracter 6 inputs an analog image signal a read by an image sensor (not shown), and a subtraction rate is set by the digital output of an inverter 7.
Note that in FIG. 2, N indicates digital parallel data.

8 is a shading correction circuit, and a subtracter 6
The shading component included in the subtracted analog image signal a and variations in the sensitivity of each bit of the image sensor are corrected, and the image signal is A/D converted and output as a digital value corrected image signal c.

_S2 is a section signal output from a timing generating circuit (not shown), and indicates the difference between the section A outside the document and the section B inside the document. Note that in FIG. 3, d is a one-line signal indicating a main scanning section. Reference numeral 9 denotes a divider which inputs the image signal clock S ₃ from the timing generation circuit, and is controlled by the section signal S ₂ to pass the image signal clock S ₃ to the outside document peak value latch circuit in the outside document section A. On the other hand, in the intra-original section B, the same image signal clock _S3 is supplied to the clock input of the intra-original peak value latch circuit 11.

The inputs of the latch circuits 10 and 11 are connected to the output of the shading correction circuit 8. Also,
The outputs of the latch circuits 10 and 11 are connected to one input of a digital comparator 13 via a divider 12, and to two inputs of an adder 14, respectively.

The segmenter 12 is controlled by the section signal _S2 , so that in the non-document section A, the output of the non-document peak value latch circuit 10 is connected to the comparator 13.
On the other hand, in the intra-document section B, the output of the intra-document peak value latch circuit 11 is input to the comparator 1.
It says to input 3.

Reference numeral 15 denotes a divider which inputs the output of the comparator 13, and is controlled by the interval signal _S2 to input the output of the comparator 13 to the extra-original peak value latch circuit 10 in the extra-original section A; In inner interval B, comparator 13
The output is inputted to an in-document peak value latch circuit 11. The output of the adder 14 is
The signal is inverted by the inverter 7 and input to the subtracter 6.

Reference numeral 16 denotes a subtraction clock generator, which generates a subtraction clock for each line and outputs the subtraction clock to the outside-of-document peak value latch circuit 10.
Enter. 17 is also a subtraction clock generation section,
A subtraction clock is inputted to the document peak value latch circuit 11 via the gate circuit 18 for each line.

Reference numeral 19 denotes a low level detection circuit 19 which inputs the corrected image signal c and the section signal _S2 , and detects the corrected image signal c whose peak value in section B within the document is below a certain level.
When the line is input, a gate control signal is sent to the gate 18 to close the gate 18.

Next, the operation of this embodiment will be explained.

After the analog image signal a is subtracted by the subtracter 6 at a subtraction rate according to the digital output of the inverter 7,
The shading correction circuit 8 corrects the shading component and variations in sensitivity of each bit of the image sensor, and performs A/D conversion, and outputs the corrected image signal c as a digital value from the correction circuit 8.

In the non-document section A of each line, the image signal clock _S3 is input to the non-document peak value latch circuit 10 via the segmenter 9, and the output of the non-document peak value latch circuit 10 is input to the segmenter 12.
At the same time, the corrected image signal c is input to the other input of the comparator 13.

Therefore, the comparator 13
The corrected image signal c is compared with the output of the extra-original peak value latch circuit 10. Based on the output of the comparator 13 indicating the comparison result, the extra-original peak value latch circuit 10 determines the level of the corrected image signal c when the level of the corrected image signal c is higher than the output level of the latch circuit 10. is newly latched at the timing of the image signal clock _S3 , while the output level of the latch circuit 10 is higher than that of the corrected image signal c.
When the output level is higher than the output level, the output level up to that point is maintained as it is. As a result, the peak value of the corrected image signal c in the out-of-document area A is latched in the latch circuit 10.

On the other hand, in the intra-document section B of each line, the image signal clock _S3 is input to the intra-document peak value latch circuit 11 via the divider 9, and the output of the latch circuit 11 is input to the in-document peak value latch circuit 11 via the divider 12. The corrected image signal c is input to the comparator 13, and at the same time, the corrected image signal c is input to the other input of the comparator 13.

Therefore, the comparator 13
The corrected image signal c is compared with the output of the in-document peak value latch circuit 11. Then, based on the output of the comparator 13 indicating the comparison result, the intra-original peak value latch circuit 11 determines that when the level of the corrected image signal c is higher than the output level of the same latch circuit 11, While the level is newly latched at the timing of image signal clock _S3 ,
When the output level of the latch circuit 11 is higher than the level of the corrected image signal c, the previous output level is maintained as it is. As a result, the peak value of the image signal c in the section B within the document is latched in the latch circuit 11.

The outputs of each of the latch circuits 10 and 11 are sent to an adder 1.
4, the signals are inverted by an inverter 7, and then input to a subtracter 6. Therefore, analog image signal a
The subtraction rate of the subtractor 6 for each latch circuit 10,
This corresponds to a value obtained by superimposing the peak values of each section A and B latched at 11.

On the other hand, the extra-original peak value latch circuit 10 subtracts its output by a predetermined amount for each line (from the end of one line to the start of the next line) using the subtraction clock input from the subtraction clock generator 16. be done. Similarly, the in-document peak value latch circuit 11 is normally controlled by the subtraction clock inputted from the clock generator 17 via the gate circuit 18.
The output is subtracted for each line.

Therefore, even if the peak values of the corrected image signal c for the lines below are lower than the peak value of the corrected image signal c in the outside-of-document section A or the inside-of-document section up to a certain line, the latch circuits 10 and 11 The latched peak values are sequentially updated according to changes in the light intensity of the light source or the density of the background of the document.

Therefore, by subtracting the analog image signal a according to the superimposed value of the peak values of each section A and B latched by the latch circuits 10 and 11 as described above, the corrected image signal c becomes the light intensity of the light source. Also, corrections are made for changes in the density of the background of the original.

It should be noted that, as mentioned above, the change in the density of the background of the original is more steep than the change in the light intensity of the light source due to aging and rise characteristics, so the peak in the original due to the subtraction clock output from the subtraction clock generator 17 is The subtraction rate of the output of the value latch circuit 11 is set to be larger than the subtraction rate of the output of the non-document peak value latch circuit 10 due to the subtraction clock output from the subtraction clock generating section 16.

As described above, in this embodiment, the subtraction rate of the out-of-document peak value latch circuit 10 that holds the peak value of the corrected image signal c in the out-of-document section A, and the peak value of the corrected image signal c in the in-document section B are adjusted. The subtraction rate of the internal peak value latch circuit 11 to be held is
Since they can be set independently from each other so as to be optimal for the rate of change in the light amount of the light source and the rate of change in the ground density of the document, the correction accuracy can be made highly accurate.

In addition, in the conventional configuration shown in FIG. 1, the time constant of the attenuation rate of the hold value of the peak hold circuit 5 is set by an analog circuit, so there are many unstable factors, which deteriorates the correction accuracy. However, in this embodiment, each of the above-mentioned subtraction rates is set by a digital quantity, so that the correction accuracy can be further improved.

By the way, even if one line of the original is completely black, if the output of the intra-original peak value latch circuit 11 is subtracted as described above, the black will be corrected to white in the lines below that. This may cause inconvenience.

However, in this embodiment, when a line whose peak value in section B within the document is below a certain level is input, the low level detection circuit 19 detects this and sends a gate control signal to the gate circuit 18. The gate circuit 18 is closed. For this reason,
Since no subtraction clock is input from the clock generator 17 to the intra-document peak value latch circuit 11, and the output of the latch circuit 11 holds the peak value up to the previous line, the above-mentioned problem does not occur.

Note that in this embodiment, since the configuration would be complicated if the actual outside-of-document section and inside-of-document section were to be detected, sections of a predetermined width at both ends of the reading scanning surface are designated as outside-of-document section A, and the remaining central section is The section is set in advance as the intra-document section B, and the extra-document section A is set to be larger than the actual outer-document section so that the intra-document section B does not protrude into the actual outer-document section. There is no problem in doing so.

However, if the internal document section B is made to protrude into the actual external document section, the white surface of the actual external document section will always appear as the peak value of the corrected image signal c in the document internal section B, and the This will cause problems in correction for changes in concentration.

Further, in this embodiment, the output of the internal peak value latch circuit 11 and the output of the external peak value latch circuit 10 are simply added by the adder 14, but each output is weighted appropriately. Addition or other calculations may be performed.

As described above, the image signal amplitude correction device according to the present invention includes an extra-original peak value holding circuit such as a latch circuit that holds the peak value of the corrected image signal in the extra-original section;
A document peak value holding circuit such as a latch circuit that holds the peak value of the corrected image signal in the section within the document is provided separately, and each of these peak value holding circuits attenuates the held peak value at a predetermined rate. By controlling the amplitude of the corrected image signal in accordance with the value calculated from the peak values held in each peak value holding circuit, gradual changes in the light intensity of the light source and steep changes in the density of the document's background can be differentiated. Since both of the above can be appropriately addressed, an excellent effect can be obtained in that the amplitude of the image signal can be corrected with high precision.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a conventional image signal amplitude correction device, FIG. 2 is a configuration diagram showing an embodiment of the image signal amplitude correction device of the present invention, and FIG. 3 is a configuration diagram showing main parts of the image signal amplitude correction device in this embodiment. FIG. 6...Subtractor, 10...Outside original peak value latch circuit, 11...Inside original peak value latch circuit, 13
...Digital comparator, 14...Adder,
19...Low level detection circuit.

Claims (1)

[Claims] 1. An amplitude changing means for changing the amplitude of the image signal to be corrected, and holding a peak value in an area outside the original of the corrected image signal obtained based on the amplitude change by the amplitude changing means, and controlling the held peak value. an extra-original peak value holding means for attenuating the correction image signal at a predetermined rate; when the peak value in the inner section is lower than a predetermined level, the peak value within the document is held as it is without attenuating the peak value, the outside peak value holding means and the peak value within the document holding means; An amplitude correction device for an image signal that controls an amplitude change rate of the amplitude change means in accordance with a value calculated from a peak value held in the image signal.