JPH05268472A - Shading correction device - Google Patents

Abstract

PURPOSE:To reduce deterioration in picture quality by eliminating the fluctuation of a shading waveform by + or -1-digit in a steady-state by means of a simple circuit without the provision of a storage means and reproducing a picture constantly. CONSTITUTION:When a shading waveform is subjected to delta demodulation from an adjacent picture element difference memory 131 storing differential data of adjacent picture elements of a shading waveform, a, demodulation control circuit 134 extracts data from the memory 131 by each picture element. Then the extracted data, a preceding picture element and a preceding to preceding picture element stored in a shift register in total three picture elements are referenced and a discrimination circuit discriminates whether or not the waveform is constant. When the waveform is constant, a reproduction level is kept independently of the differential data by acting a delta demodulator 132.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus such as a facsimile apparatus, and more particularly to a shading correction apparatus for reading an image by using solid-state scanning elements arranged in the main scanning direction.

[0002]

2. Description of the Related Art As shown in FIG. 1, the flow of an image signal in a facsimile apparatus is such that a reading section 1 first reads an object to be read, converts it into a digital signal, encodes it in an encoding section 2, and encodes it in a communication line through a modem 5. Sent to. On the contrary, the signal sent from the communication line is decoded by the decoding unit via the modem 5 and printed on the recording paper by the recording unit.

As shown in FIG. 2, a block diagram of a reading section of this type of apparatus has hitherto been applied to a document 10 from a light source 11 and reflected light thereof is input to a line sensor 12 for main scanning 1.
The image signal for the line is obtained. The obtained image signal is converted into a digital signal by the A / D converter 13, and the shading correction unit 14 causes distortion in the reading system, that is, the reading distortion of the photoelectric conversion unit caused by fluctuations in the light amount of the light source and variations in the reading sensor. The so-called shading distortion is corrected and the binarization unit 15 obtains binary data. The shading correction unit 14 reads the white reference plane in advance and stores the shading waveform. However, if the brightness level of each pixel for one line of the output of the A / D converter 13 is stored as it is, there is a problem that the memory amount increases. It was

As means for solving this problem, Japanese Patent Laid-Open No. 3-1
There is a technology described in 08955. This technique is shown in Figure 3.
The block structure is as shown in (1), and a so-called delta modulation method is used in which a changed portion of the brightness level of an adjacent pixel is detected within a fixed time and binarized according to the result. By this method, the difference in the brightness level is encoded and the number of bits is reduced and stored. In other words, when storing the shading waveform, the A / D converter 13
Output from the delta modulator 130 is differentially encoded, the encoded data is stored in the adjacent pixel difference memory 131, and when the image data is corrected next, the encoded data is extracted from the adjacent pixel difference memory 131.
2, the shading waveform is reproduced, and the shading correction circuit 133 corrects the input image signal using the reproduced shading waveform.

[0005]

In the prior art, as shown in FIG. 4, a shading waveform (A / D output signal when encoded into 1 bit per pixel (1, 0 depending on whether it is larger or smaller than the previous pixel) is used. ) Is constant, the reproduced shading waveform fluctuates by ± 1 digit, which affects the subsequent image processing unit and causes deterioration in image quality. That is, in a shading waveform storage system in which a shading waveform is delta-modulated and delta-demodulated for one pixel and stored and reproduced, when the shading waveform portion in a constant level state is delta-modulated and binarized, The demodulated waveform is not reproduced at a constant level, and there is a problem that fluctuation of ± 1 digit occurs.

An object of the present invention is to provide a shading correction apparatus with little deterioration in image quality by removing the fluctuation of ± 1 digit in this constant state by a simple circuit without using a storage means and reproducing it constantly. It is in.

[0007]

As shown in FIG. 5, a delta modulator 130 which encodes a shading waveform into 1 bit per pixel, an adjacent pixel difference memory means 131 which stores encoded data, and an encoded pixel difference memory means 131. Delta demodulator 132 for reproducing a shading waveform from 1-bit data
And a demodulation control circuit 13 for controlling the delta demodulator 132
4 and the shading correction circuit 133.

Further, as shown in FIG. 15, a delta modulator 130 which encodes a shading waveform into 1 bit per pixel.
An adjacent pixel difference memory means 131 for storing encoded data, a delta demodulator 132 for reproducing a shading waveform from encoded 1-bit data, and a filter circuit 135 for filtering and correcting the reproduced shading waveform. , And shading correction circuit 133
Can be achieved with.

[0009]

In the delta demodulation of the shading waveform from the adjacent pixel difference memory 131 which stores the difference data of the adjacent pixels of the shading waveform, the demodulation control circuit 134 is provided to determine whether or not the waveform is in a constant state. In the case of a constant state, it acts on the delta demodulator 132 to hold the reproduction level (prohibit up / down of delta modulation) regardless of the difference data.

Further, a high-pass component (fluctuation of "1" or "0") of the shading waveform reproduced by delta demodulation is removed by a low-pass filter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 6 shows an embodiment of the delta modulator 130. Up the initial value of shading waveform (the value of the first pixel)
When the input signal of the second pixel is input next, the comparator 130a compares it with the initial value and encodes "1" or "0" depending on the magnitude. Then, in the up / down counter 130b based on the coded signal, (up by 1 digit if the coded signal indicates a large "1", down by 1 digit if the coded signal is a small "0") second pixel Of the third pixel is compared with the input signal of the third pixel by the comparator 130a and encoded. Similarly, coding is performed by comparing the input signal level (current pixel) with the signal level reproduced through the immediately preceding (previous pixel) code decoding.

FIG. 7 shows an example of the delta demodulator 132. The delta demodulator can be composed of one up / down counter 132a.
Initial value of shading waveform as the initial value (value of the first pixel)
Is set and the current value is changed by the coded signals “1” and “0”.
It goes up / down and decrypts.

The shading correction circuit 133 shown in FIG. 5 can be realized by a divider. As another method, it can be realized by multiplying the reciprocal of the shading waveform with the image signal by a reciprocal table and a multiplier, or by a table.

FIG. 8 shows a demodulation control circuit 1 which is a feature of the present invention.
34 shows an example. When reproducing the shading waveform, data is extracted for each pixel from the adjacent pixel difference memory 131 in which the shading waveform is differentially encoded and stored.
The determination circuit 134c discriminates a specific pattern by referring to the three pixels of the fetched data and the data of the previous pixel and the data of the previous pixel stored in the shift registers 134a and 134b, and controls the delta demodulation process that follows. For example, the data fetched from the adjacent pixel difference memory 131 is the data of the (n + 1) th pixel, the data stored in the shift register 134a is the nth pixel, and the data stored in the shift register 134b is the (n-1) th pixel data. And As a characteristic of the encoded data when the shading waveform is in a constant state, there are "1", "0" such as "1", "0", "1", "0", "1", "0". Since it is repeated, the nth pixel is set as a processing pixel by using this feature, and n + 1, n,
When the data of the n-1 pixel is "1", "0", "1" or "0", "1", "0", a signal (Enable signal) is output to the delta demodulator and the level of the reproduced waveform is output. Are held (“0”: set to the same level as the previous pixel). However, simply referring to the (n + 1) th, (n) th, (n-1) th pixel causes an offset of one digit, and therefore the Enable signal is updated at the even-numbered pixel from the pixel position where the value becomes “0”. The discrimination circuit can be realized by a circuit as shown in FIG. 9 or a table. Truth tables of the discrimination circuit 134c and the demodulation control circuit 134 are shown in FIGS. When the up signal is "1", the demodulator increments the current level by +1 and when the down signal is "1", the current level is incremented by -1. In the EnableA signal, the data of the n + 1, n, and n−1 pixels is “1”, “0”, “1” or “0”,
When it is "1" or "0", it becomes "0", the EnableB signal is the previous pixel EnableA-1 signal is "0", and the previous pixel Enable is
It becomes "0" when the B-1 signal is "1". Also, Enab
The le signal becomes "0" when either EnableA or EnableB is "0". When the Enable signal is "0", the demodulator holds the level of the reproduced waveform. That is, when the shading waveform is in a constant state, it is possible to reproduce the shading waveform close to the actual shading waveform by keeping the reproduction waveform constant.

FIG. 13 shows an example of the demodulation control circuit 134 having a filter circuit.

When reproducing the shading waveform, the high-pass filter is used to detect a portion having a high spatial frequency (repetition of "1" and "0") by the data from the adjacent pixel difference memory 131 in which the shading waveform is differentially encoded and stored. Detect and output EnableA signal.

FIG. 14 shows an example of windows and coefficients of a high pass filter.

When the input is "1", "0", "1", the output is "1", and the input is "0", "1",
In the case of "0", the output becomes "-1". Since the absolute values of the other outputs are smaller than "1", they can be "0" by truncating at the end of the calculation. In other words, output “0”
Those that are not can be detected as high spatial frequency portions (repetition of "1" and "0"). The coefficient of this high-pass filter may be made variable by providing a register and setting a value.

Another embodiment of the shading correction unit according to the present invention will be described with reference to FIGS. The shading waveform is differentially encoded by the delta modulator 130,
The difference encoded data is stored in the difference data memory 131. Then, based on the difference data, the delta demodulator 13
The shading waveform is reproduced by demodulation in step 2, and the high-frequency component (fluctuation of "1" or "0") of the shading waveform reproduced by the low-pass filter circuit is removed by the low-pass filter to correct the shading waveform.

FIG. 16 shows an example of windows and coefficients of the low-pass filter circuit.

Since the shading waveform data demodulated by the delta demodulator 132 is multivalued data, for example, "3
When the data “1”, “30”, “31”, “30” is input, the output becomes “30.5” and the fluctuation of 1 digit is suppressed. A variable may be provided by setting a value.

Further, another embodiment and modification of the present invention will be described. In the above embodiment, the reading section of the facsimile is described, but it can be applied to a scanner device or a copying machine. Further, the shading correction unit of the present invention is suitable for an LSI because the hardware scale is small, and the image processing unit 16 of the reading unit in FIG. 2 may be configured by a one-chip LSI.

[0024]

According to the present invention, even if the shading waveform does not change, the demodulated reproduced waveform does not fluctuate by ± 1 digit, and the actual shading waveform can be reproduced substantially faithfully. Thus, a high quality shading correction device can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a block configuration example of a facsimile apparatus.

FIG. 2 is a diagram illustrating a block configuration example of a reading unit of a facsimile device.

FIG. 3 is a diagram illustrating a block configuration example of a conventional shading correction unit.

FIG. 4 is a diagram showing a modulation signal and a demodulation signal using delta modulation / demodulation of 1 bit per pixel.

FIG. 5 is a diagram showing a block configuration of a shading correction unit according to the present invention.

FIG. 6 is a diagram showing an example of a delta modulator.

FIG. 7 is a diagram illustrating an example of a delta demodulator.

FIG. 8 is a diagram showing an example of a demodulation control circuit according to an embodiment of the present invention.

FIG. 9 is a diagram showing an example of a discrimination circuit according to an embodiment of the present invention.

FIG. 10 is a diagram showing a truth table of EnableA of the demodulation control circuit.

FIG. 11 is a diagram showing a truth table of EnableB of the demodulation control circuit.

FIG. 12 is a diagram showing an enable truth table of the demodulation control circuit.

FIG. 13 is a diagram showing an example of a demodulation control circuit using the filter of the embodiment of the present invention.

FIG. 14 is a diagram showing an example of windows and coefficients of a high-pass filter.

FIG. 15 is a diagram showing a block configuration example of a shading correction unit of the present invention.

FIG. 16 is a diagram showing an example of windows and coefficients of a low-pass filter.

[Explanation of symbols]

10 ... Original, 11 ... Light source, 12 ... Sensor, 13 ... A / D
Converter, 14 ... Shading correction section, 15 ... Binarization section, 16 ... Image processing section, 130 ... Delta modulator, 131
... Adjacent pixel difference data memory, 132 ... Delta demodulator,
133 ... Shading correction circuit, 134 ... Demodulation control circuit, 134a ... Shift register, 134b ... Shift register, 134c ... Discrimination circuit, 134d ... High pass filter circuit, 135 ... Low pass filter circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keisuke Nakajima 4026 Kujimachi, Hitachi City, Hitachi, Ibaraki Prefecture, Hitachi Research Laboratory Ltd. AV equipment division

Claims (9)

[Claims] 1. A delta modulator for encoding a shading waveform, a differential data memory for storing the output of the delta modulator, and a delta demodulator for reproducing a shading waveform from the encoded data of the differential data memory. In a shading correction device for correcting shading using the demodulation control means for signal processing the output from the differential data memory to generate a control signal for waveform correction, and the output from the differential data memory based on the control signal. And a delta demodulation means for correcting the shading correction device. 2. The shading correction apparatus according to claim 1, wherein the demodulation control means and the delta demodulation means detect a spatial frequency of the shading waveform, and correct the shading waveform at a predetermined specific spatial frequency. A shading correction apparatus characterized by comprising means. 3. The shading correction apparatus according to claim 2, wherein the means for detecting the spatial frequency detects whether the spatial frequency is equal to or higher than a specific spatial frequency by using a spatial frequency filter. 4. A shading correction apparatus according to claim 3, wherein the coefficient of the spatial frequency filter can be made variable. 5. The shading correction apparatus according to claim 2, wherein the means for detecting the spatial frequency detects the spatial frequency by referring to data before and after the processed pixel of the difference data memory. apparatus. 6. A delta modulator for encoding a shading waveform, a differential data memory for storing the output of the delta modulator, and a delta demodulator for reproducing a shading waveform from the encoded data of the differential data memory. A shading correction apparatus for correcting shading using the shading correction apparatus, wherein the reproduced shading waveform from the demodulator is corrected by a spatial frequency filter. 7. The shading correction apparatus according to claim 6, wherein the coefficient of the spatial frequency filter can be made variable. 8. A shading correction apparatus according to claim 1, which is applied to a fax machine, a scanner apparatus, and a copying machine. 9. The shading correction apparatus according to claim 1, wherein at least the A / D converter, the shading correction unit, and the binarization unit are configured by a one-chip LSI.