JP3057709B2 - Image processing system and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a small memory capacity and a simple MTF in image processing of a facsimile machine or a scanner.
The present invention relates to an image processing method capable of increasing gradation by using a correction circuit.

[Conventional technology]

Although the television image is a halftone image, the halftone is represented by a combination of black and white binary values by a systematic dither method or the like. In still image communication, when transmitting document information, binary information is used for band compression. Recently, document information is also converted to a dither method or the like due to the necessity of halftone reproduction.
Sent with value information.

Therefore, conventionally, in an image processing apparatus such as a facsimile apparatus, a normal binary image (MTF correction) and a halftone image have been processed with the same bit length.

The transmitted image can be physically evaluated using a test chart (test pattern), but basic constants such as line density and maximum image frequency can be reproduced on the receiving side by waveform observation. You can check whether it is done. The MTF (Modulation Transfer Function) is a method for expressing the frequency characteristics of a system. In a facsimile, a received image of a 5-part pattern portion of a test _chart is _measured, and the maximum value E _mox and the minimum value at each spatial frequency are measured. Value E _min
, And the MTFR is calculated by the following equation.

In a recent facsimile machine, an original is read by an image sensor, an analog signal output from the original is converted into a 4-bit pixel signal by A / D conversion, and then MTF correction is performed.
Valued. The MTF correction is to correct the deteriorated image information signal by compensating for the distortion of the spatial frequency characteristic in the transmission system in the reading device. This is corrected by a spatial filter.

 FIG. 5 is an explanatory diagram of the operation of the MTF correction circuit.

In the MTF correction, a 3 × 3 matrix is formed and corrected by a spatial filter. As shown in FIG. 5A, an original is first read by a reading line and stored in a 3 × 3 matrix. The data is read from or written to the line memories (1) and (2) to form a 3 × 3 data (multi-valued) matrix.

Now, when the 3 × 3 matrix of A to I in FIG. 5B is corrected by a spatial filter as shown in FIG. 5C, the correction data E ′ of the target pixel E is It is calculated by performing an operation such as an equation.

Regarding the halftone processing and MTF correction of facsimile, for example, see “Ricoh Technical Report No.8, N
OVEMBER, 1982, pp. 52-59.

[Problems to be solved by the invention]

As described above, in a conventional image processing system such as a facsimile apparatus, normal binary image processing (MTF correction processing) and halftone processing are performed with the same bit length.

Recently, the number of tones has been increased in facsimile apparatuses in order to improve the image quality of halftones (for example, from 16 tones).
Therefore, the number of bits of multi-valued image data is also increasing (for example, from 4 bits / pixel to 6 bits / pixel).

As a result, in image processing in which a matrix is formed by multi-valued data and an operation is performed using a spatial filter as in MTF correction, the memory capacity required for matrix formation is increased (for example, Number of bits from 4 × 2 to 6
× 2).

However, such a demand for higher gradation is increasing only for a halftone image, and is not always required for a normal binary image.

An object of the present invention is to solve such a conventional problem and to provide an image processing method capable of increasing the gradation by using a small memory capacity and a small MTF correction circuit.

[Means for solving the problem]

In order to achieve the above object, the image processing method of the present invention comprises:
The multi-valued digital image signal to be subjected to halftone processing is processed with a predetermined bit length for high gradation, and the multi-valued digital image signal to be processed by the spatial filter is processed with bits shorter than the above-mentioned bit length. In this case, the threshold value is switched by one control signal.

[Action]

In the present invention, the number of bits in the processing of the halftone image and the processing of the normal binarized image are changed, thereby realizing a higher halftone level without increasing the memory. That is,
In the case of ordinary binary data, only the upper 4 bits of the 6-bit data are valid, the lower 2 bits are canceled, and the image data is treated as 4 bits. On the other hand, in the case of halftone image data, 6-bit data (64 gradations) is handled as it is, and binarization is performed using a 6-bit dither pattern threshold value. Switching between normal binary data and halftone data is performed by a multiplexer using a control signal. As a result, high gradation can be achieved as in the related art, and the amount of memory can be significantly reduced, and the MTF correction circuit can be of a small scale as compared with the case of processing with the same bit length.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an image processing apparatus showing one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a CCD (C
harge Coupled Device), 2 is an analog processing circuit, 3
Is an A / D conversion circuit for converting an analog signal into a digital signal, and 4 is a 3 × for performing MTF correction as shown in FIG.
3 is a matrix circuit, 5 is an MTF operation circuit of a logic part for calculating the above equation (2), 6 is a RAM, 7 is a multiplexer (1) for synthesizing a normal binary image and a halftone image, and 8 is
A binarization circuit for binarizing a 6-bit pixel and converting it to 1-bit / 5-pixel, and a multiplexer 9 for synthesizing each value of a binary threshold and a dither threshold.
It is.

The original is irradiated with light, and the reflected light is received by the CCD1.
The image signal photoelectrically converted by the CCD 1 is subjected to analog processing such as DC reproduction, white waveform correction, and peak hold in an analog processing circuit 2. In this case, the white waveform correction is performed with 6-bit data. The analog processed image signal is
The D conversion circuit 3 forms 6-bit multi-value digital image data.

Here, the signal path is separated into normal binarization processing and halftone processing. The same data is sent out on both paths, but valid data is selected by multiplexer 7.

(A) Normal binarization In normal binarization processing, upper 4 bits of 6 bits are used as valid data, lower 2 bits are canceled, and image data is deleted.
Data is treated as 4 bits. When the image data is 4 bits, a memory having a data length of 4 bits × 2 lines = 8 bits is required in order to form a 3 × 3 matrix 4 for MTF correction. The 4 × 2 bits are fed back to the analog processing circuit 2 via the RAM 6 for white waveform correction data. White waveform correction is also performed with 4 bits. The 6-bit white waveform correction data controls the upper 4 bits for correction and fixes the lower 2 bits. Therefore, the total memory is 8 + 4 = 12 bits long. The MTF operation circuit 5 also performs an operation with a 4-bit length, and inputs the result to a binarization circuit 8 via a multiplexer 7, where the result is also binarized by a 4-bit binary threshold.

Thus, in this embodiment, the bit length of the memory is 4+
Since only 4 + 4 = 12 bits are required, the bit length of the memory is reduced as compared with the case where the processing is directly performed with 6 bits, and the bit operation in the MTF operation circuit 5 is also reduced from 6 bits to 4 bits. I'm done.

(B) Halftone In the halftone process, the data is input from the A / D conversion circuit 3 to the binarization circuit 8 via the multiplexer 7 via the bypass path, and is directly converted into 6-bit data (64 gradations).
Binarization is performed using the threshold value of the bit dither pattern. At this time, the white waveform correction is performed using all 6 bits.

The dither threshold value for the binarization of the halftone is 6 bits from the circuit 10, and the binary threshold value for the binarized image data is 4 bits from the circuit 11. Is input to the binarization circuit 8 via

Switching between normal binary (MTF correction) and halftone is performed by one control signal, and each control signal of MTF / halftone is input to multiplexers 7 and 9, respectively. , Can be switched.

FIG. 2 is a diagram showing an example of use of a memory according to the present invention.

During normal binarization, of the 12 bit length b ₀ ~b _11,
4 bits of b ₀ ~b ₃ white waveform correction, 4 bit b ₄ ~b ₇ in a matrix line memory (1), because it uses 4 bit b ₈ ~b ₁₁ in a matrix line memory (2) ,
A total of 12 bits is sufficient. Compared to the conventional case where 6 bits are used, 18-12 = 6 bits are required.

On the other hand, at the time of the halftone, for white waveform correction, using a 6 bit b ₀ ~b _5.

FIG. 3 is a diagram showing a comparison of the number of memory bits between the conventional and the present invention.

In the conventional method, since 6 bits are used for white waveform correction and 6 bits × 2 are used for the matrix, the total is 18 bits, and three 8-bit RAMs are required.

On the other hand, in the method of the present invention, since 4 bits are used for white waveform correction and 4 bits × 2 are used for the matrix, a total of 12 bits is required, and only two 8-bit RAMs are required.

FIG. 4 is a control flowchart of image processing showing one embodiment of the present invention.

First, it is determined whether the image is halftone or binary (step 401). In the case of halftone, all 6-bit data is made valid (step 402). Then, dither threshold is selected by selecting dither threshold (step 403), and binarization is performed (step 40).
7).

In the case of binary image data, only the upper 4 bits are made valid (step 404), MTF correction is performed on the 4 bits (step 405), and a binary threshold is selected as the threshold value (step 405). (Step 406) Binarization is performed (Step 407).

〔The invention's effect〕

As described above, according to the present invention, the bit length of multi-value data is used as it is in the case of halftone,
When the value is used, the bit length is reduced and used, so that the memory amount can be reduced and the scale of the MTF correction circuit can be reduced as compared with the case of processing with the same bit length.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image processing apparatus showing one embodiment of the present invention, FIG. 2 is a diagram showing an example of using a memory in the present invention,
FIG. 3 is a comparison diagram of the number of memory bits in the prior art and the present invention, FIG. 4 is a control flowchart of image processing showing one embodiment of the present invention, and FIG. 5 is a configuration diagram of an MTF correction circuit. . 1: CCD, 2: Analog processing circuit, 3: A / D conversion circuit, 4: MTF matrix circuit, 5: MTF operation circuit, 6: RAM, 7: Multiplexer, 8: Binarization circuit, 9: Multiplexer, 10 : Dither threshold setting circuit, 11: binary threshold setting circuit.

Claims (3)

(57) [Claims] An analog processing circuit for performing at least analog processing including at least white waveform correction on an input analog image signal, and an analog / digital converter for converting an analog image signal output from the analog processing circuit from analog to digital. A conversion circuit, an MTF correction matrix for inputting only the upper few bits of the digital image signal output from the analog / digital conversion circuit, and performing an operation on the digital image signal input to the MTF correction matrix An MTF arithmetic circuit for performing MTF correction by writing a digital image signal to the matrix for MTF correction, forming a line memory for reading out, and feeding back white waveform correction data to the analog processing circuit
A digital image signal output from the analog-to-digital conversion circuit by a control signal for controlling switching between pseudo halftone processing and simple binary processing with respect to the input image signal; A first multiplexer that switches and outputs a digital image signal output from the first multiplexer, a second multiplexer that switches one of a binary threshold and a dither threshold and adds to a binarization circuit by the control signal, And a binarizing circuit for binarizing the digital image signal output from the first multiplexer based on a threshold output from the second multiplexer. 2. The first multiplexer selects one of a processed halftone image and a simple binary image according to the control signal, and inputs a signal of the selected image to a binarization circuit. The binarization circuit receives the dither threshold value or the binary threshold value selected by the second multiplexer, and outputs the pixel signal output from the first multiplexer in the selected mode. 2
The image processing system according to claim 1, wherein the value is converted into a value. 3. A step of deciding between pseudo halftone processing and simple binarization processing for an inputted analog image signal, and when halftone processing is selected, all multi-valued bit data are made valid. Outputting an image signal to a binarization step and selecting dither threshold as a threshold; and when simple binarization processing is selected, only the upper several bits of the multi-valued bit data Enable, perform MTF correction with the upper few bits, output an image signal to the binarization step, and select a binary threshold as a threshold; and select the image signal output from the step, respectively. A binarizing step of binarizing with a threshold.