JPH10304362A - Image signal processing unit and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce image deterioration caused by rounding of arithmetic operations conducted in a quantization means as much as possible and to attain high compression processing. SOLUTION: This method employs; a division means 103 that divides a received image signal into a plurality of blocks consisting of a prescribed number of pixels; a transformation means 104 that applies orthogonal transformation to image data of each block division by the division means 103; a quantization means 106 that quantizes the image data orthogonally transformed by the transformation means 104; a coding means 107 that applies variable length coding to the quantized image data; and a means that adjusts the code after quantization and variable length coding to have a code in a range consisting of a prescribed number of blocks. Then the method for rounding an arithmetic operation of the quantization means 106 is selected based on the received data and a quantization characteristic of the quantization means 106 in order to conduct image compression with less image quality deterioration and to reduce a maximum value of a quantization error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing apparatus and method, and more particularly, to a method for compressing analog-to-digital converted image data, decompressing the same after passing through a transmission medium or a recording medium. The present invention also relates to an image signal processing apparatus and method for outputting an image signal by performing digital-to-analog conversion.

[0002]

2. Description of the Related Art An image signal is divided into blocks each composed of a plurality of pixels, and the data is subjected to an orthogonal transformation. An image signal processing device that performs variable-length encoding and transmits or records the encoded data has been considered. Hereinafter, an example of a conventional image signal processing device will be briefly described.

FIG. 4 shows a configuration diagram of a conventional image signal processing apparatus. In FIG. 4, reference numeral 201 denotes an input signal of an interlaced analog image signal, 202 denotes an analog-to-digital converter for converting an analog image signal into a digital image signal, and 203 denotes a block (for example, a quadrature transform of the digital image signal). , 8 pixels vertical x 8 horizontal
Block dividing unit for dividing the image into pixels.

[0004] Reference numeral 204 denotes a DCT processing unit for orthogonally transforming a block-divided digital image signal. 205
Means that a plurality of blocks (for example, 30
This is a code amount estimating unit for estimating a quantization characteristic so as to obtain a predetermined code amount when collectively quantizing and performing variable length coding.

[0005] Reference numeral 206 denotes a quantization unit which quantizes the data orthogonally transformed by the DCT processing unit 204 by using the quantization characteristic estimated by the code amount estimation unit 205. A variable-length coding unit that performs variable-length coding on the converted data. A data processing unit 208 transmits or records an image signal encoded by the variable length encoding unit, and outputs a signal 209 to be transmitted or recorded.

FIGS. 5A and 5B show the input of a quantization block on the X-axis and the output of the quantization block on the Y-axis, and the quantization characteristic is Y = X ÷ N. FIG. 5 (a)
5 shows a case where truncation is performed by calculation, and FIG. 5B shows a case where rounding is performed by calculation.

In FIG. 5A and FIG. 5B, the broken lines indicate the calculation result of Y = X ÷ N, and the solid line indicates the result of rounding. , Rounding such as truncation and rounding was performed.

[0008]

In the conventional image signal processing apparatus, when the same data is quantized with the same quantization characteristics, the output is (a) smaller when rounding down than when rounding off. More zeros in the data. Also,
(B) Since the data value is reduced, the compression efficiency of the output data of the variable length coding unit 207 may be improved.

Therefore, when the truncation is performed, the quantization step becomes smaller because the N can be made smaller in the quantization characteristic Y = X ÷ N, as compared with the case where the rounding is performed. There is an advantage that high quality image compression can be performed.

[0010] However, there is a demerit that the maximum value of the quantization error increases when truncation is performed. As described above, the conventional rounding method in the quantization operation has advantages and disadvantages, and there is a problem that high-quality image compression cannot be performed by using one kind of rounding method. Was.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to perform high-quality image compression and to perform quantization with little image quality deterioration.

[0012]

According to the present invention, there is provided an image signal processing apparatus comprising: dividing means for dividing an input image signal into a plurality of blocks each having a predetermined number of pixels; and each of the blocks divided by the dividing means. Transforming means for orthogonally transforming the image data, quantizing means for quantizing the image data orthogonally transformed by the transforming means, encoding means for performing variable-length encoding on the quantized image data, Means for ensuring that the number of encoded and variable-length-encoded codes is within a range of a predetermined number of blocks. Switching is performed according to the data value input to the means and the quantization characteristic of the quantization means.

Another feature of the present invention is that
The quantization means performs rounding of truncation by a quantization operation when the input data value is less than a predetermined value, and rounds off by rounding by a quantization operation when the input data value is a predetermined value or more. It is characterized by performing.

According to another feature of the present invention, when the input data value is less than a first predetermined value, the quantization means performs rounding of truncation by a quantization operation and receives the input data value. If the input data value is greater than or equal to the first predetermined value and less than the second predetermined value, rounding by rounding is performed by a quantization operation, and if the input data value is equal to or more than a third predetermined value, a quantization operation is performed. It is characterized by rounding to seven rounds.

According to another feature of the present invention, the encoding means rearranges the orthogonally-transformed data from low frequency components, so that the number of continuous zeros of the data and the non-zero number of zeros are determined. Huffman coding is performed by combining data.

Further, according to the image signal processing method of the present invention, a dividing process of dividing an input image signal into a plurality of blocks each composed of a predetermined number of pixels, and an image data of each block divided by the dividing process are orthogonalized. A conversion process for converting;
A quantization process for quantizing the image data orthogonally transformed by the conversion process, an encoding process for variable-length encoding the quantized image data, and a predetermined number of the quantized and variable-length encoded codes. In the image signal processing method of performing a process of obtaining a code amount in a range of a block, wherein a method of rounding the operation performed in the quantization process is performed by using the input data value and the quantization in the quantization process. Switching is performed according to characteristics.

According to another feature of the present invention, in the quantization process, when the input data value is less than a predetermined value, rounding of truncation is performed by a quantization operation, and the input data value is rounded. Is greater than or equal to a predetermined value, a rounding operation is performed by a quantization operation.

According to another feature of the present invention, in the quantization process, when the input data value is smaller than a first predetermined value, the data is rounded by truncation by a quantization operation, and the input data value is input. If the input data value is greater than or equal to the first predetermined value and less than the second predetermined value, rounding by rounding is performed by a quantization operation, and if the input data value is equal to or more than a third predetermined value, a quantization operation is performed. It is characterized by rounding to seven rounds.

According to another feature of the present invention, in the encoding process, the orthogonally transformed data is rearranged from the one having a low frequency component, and the number of consecutive zeros of the data and the non-zero data are determined. Huffman coding is performed by combining data.

Since the present invention comprises the above technical means, the rounding method in the operation for performing the quantization is selected according to the orthogonally transformed data value, so that the compression efficiency can be reduced according to the input data value. It is possible to improve the image quality and reduce the image quality deterioration due to the quantization.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of an image signal processing apparatus and method according to the present invention will be described below with reference to the drawings. FIG.
FIG. 2 is a block diagram illustrating a configuration of an image signal processing device according to the present embodiment. In FIG. 1, reference numeral 101 denotes an input signal of an interlaced analog image signal, and reference numeral 102 denotes an analog-digital converter for converting the input analog image signal into a digital image signal.

Reference numeral 103 denotes a block division processing unit that divides the digital image signal into blocks (for example, 8 pixels vertically × 8 pixels horizontally) that are orthogonally transformed. 104 denotes a DCT processing unit that orthogonally transforms the divided digital image signal. , 10
5 denotes a plurality of orthogonally transformed blocks (for example, 30
This is a code amount estimating unit for estimating a quantization characteristic such that a predetermined code amount is obtained when the data is collected and quantized and subjected to variable-length coding.

Reference numeral 106 denotes a quantization unit that quantizes the image data orthogonally transformed by the DCT processing unit 104 with the quantization characteristics estimated by the code amount estimation unit 105. 110
Is a quantization control unit that controls the quantization characteristics of the quantization unit 106, 107 is a variable length coding unit that performs variable length coding on the quantized image data, and 108 is a unit that transmits the coded image data. Alternatively, it is a data processing unit for recording, and outputs an output signal 109 to be transmitted or recorded.

The variable-length coding unit 107 performs the Huffman coding by rearranging the orthogonally transformed data in ascending order of frequency components and combining the continuous number of zeros of data with non-zero data.

At this time, in the Huffman coding, the data amount tends to be highly compressed as the number of zeros of the data increases or as the value of the data decreases. The quantization unit 106 selects and performs rounding of rounding down and rounding off in the calculation of quantization under the control of the quantization control unit 110.

As shown in FIG. 2, for example, when the quantization characteristic is Y = X ÷ N, if the input to the quantization unit 106 is less than N, the quantization operation is truncated.
Is operated to perform rounding when the input of is greater than or equal to N.

The reason is as follows: (a) When the input of the quantization unit 106 is smaller than N, the value is reduced to zero by truncation, so that high compression in Huffman coding can be expected. Also,
(B) When the input of the quantization unit 106 is N or more, even if truncation is performed, the value does not become zero, and high compression in Huffman coding cannot be expected. Therefore, rounding with less quantization error is performed. This is because it is more advantageous.

(Second Embodiment) In the first embodiment described above, the rounding of the quantization operation in the quantization unit 106 is performed in accordance with the quantization characteristics shown in FIG. In the embodiment, as shown in FIG. 3, when the input of the quantization unit 106 is smaller than N, the truncation is performed by the quantization operation, and when the input of the quantization unit 106 is equal to or larger than N and smaller than 2N, the quantization is performed. The operation is performed by rounding off to seven, and the input of the quantization unit 106 is 2N.
In the above case, the operation is performed so as to round off in the quantization operation.

Here, the number of rounding methods and the boundaries of the rounding control are not limited to those described in the above embodiment. Further, the rounding method in the quantization operation is not limited to the truncation, the rounding, and the rounding described in the embodiment.

(Other Embodiments of the Present Invention) The present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), and is applied to one device (for example, a copying machine). , A facsimile machine).

Further, in order to realize various functions so as to realize the functions of the above-described embodiments, the functions of the above-described embodiments are realized by a device connected to the various devices or a computer in a system. The present invention also includes a program that is implemented by supplying the program code of the software described above and operating the various devices according to a program stored in a computer (CPU or MPU) of the system or apparatus.

In this case, the program code of the software implements the functions of the above-described embodiment, and the program code itself and means for supplying the program code to the computer,
For example, a storage medium storing such a program code constitutes the present invention. As a storage medium for storing such a program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM,
A magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the supplied program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) or other operating system running on the computer. Needless to say, the program code is also included in the embodiment of the present invention when the functions of the above-described embodiment are realized in cooperation with application software or the like.

Further, after the supplied program code is stored in a memory provided in a function expansion board of a computer or a function expansion unit connected to the computer, the function expansion board or the function expansion unit is specified based on the instruction of the program code. It is needless to say that the present invention also includes a case where a CPU or the like provided in the first embodiment performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0035]

As described above, according to the present invention, the rounding method in the tracing operation for performing the quantization is selected according to the value of the orthogonally transformed data. As a result, the compression ratio can be improved, and the image quality degradation due to quantization can be reduced, and high-quality image transmission and / or recording with little image quality degradation can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image signal processing device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a state of rounding in an operation for performing quantization in the first embodiment.

FIG. 3 is a diagram illustrating a state of rounding in an operation for performing quantization in a second embodiment.

FIG. 4 is a block diagram illustrating an example of a conventional image signal processing device.

FIG. 5 is a diagram showing a state of rounding in an operation for performing quantization.

[Explanation of symbols]

 Reference Signs List 101 input signal of analog image signal 102 analog-digital conversion unit 103 block division processing unit 104 DCT processing unit 105 code amount estimation unit 106 quantization control unit 107 variable length coding unit 108 data processing unit 109 output signal 110 quantization control unit

Claims (8)

[Claims] A dividing unit that divides an input image signal into a plurality of blocks each including a predetermined number of pixels; a transforming unit that orthogonally transforms image data of each block divided by the dividing unit; Quantization means for quantizing the image data orthogonally transformed by the means, coding means for performing variable-length coding on the quantized image data, and a block having a predetermined number of blocks obtained by performing the quantization and variable-length coding. An image signal processing apparatus having a code amount in a range of: a method of rounding an operation performed by the quantization means, wherein a data value input to the quantization means and a value of the quantization means An image signal processing apparatus characterized in that switching is performed according to quantization characteristics. 2. The quantization means according to claim 1, wherein said input data value is smaller than a predetermined value, and said operation means performs rounding of truncation by a quantization operation. 2. The image signal processing apparatus according to claim 1, wherein rounding is performed by rounding. 3. The quantization means performs rounding of truncation by a quantization operation when an input data value is less than a first predetermined value, and when the input data value is equal to or more than a first predetermined value. When the data value is less than the second predetermined value, rounding by rounding is performed by a quantization operation, and when the input data value is equal to or more than the third predetermined value, rounding by rounding off by a quantization operation is performed. The image signal processing device according to claim 1, wherein: 4. The encoding means according to claim 1, wherein said orthogonally transformed data is rearranged in descending order of frequency components, and Huffman encoding is performed by combining a continuous number of zeros of data and non-zero data. Claim 1 to claim
4. The image signal processing device according to claim 3. 5. A division process for dividing an input image signal into a plurality of blocks each including a predetermined number of pixels; a conversion process for orthogonally transforming image data of each block divided by the division process; A quantizing process of quantizing the image data orthogonally transformed by the above, an encoding process of performing variable length coding on the quantized image data, and a code having the quantized and variable length coded in a predetermined number of blocks. An image signal processing method for performing a process of providing a code amount within a certain range, wherein a method of rounding an operation performed in the quantization process is determined according to the input data value and a quantization characteristic in the quantization process. An image signal processing method characterized in that the image signal is switched by switching. 6. The quantization process according to claim 1, wherein when the input data value is less than a predetermined value, rounding down is performed by a quantization operation, and when the input data value is not less than a predetermined value, the quantization operation is performed. The image signal processing method according to claim 5, wherein the rounding is performed. 7. The quantization process according to claim 1, wherein when the input data value is less than a first predetermined value, rounding down is performed by a quantization operation, and when the input data value is not less than a first predetermined value. When the data value is less than the second predetermined value, rounding by rounding is performed by a quantization operation, and when the input data value is equal to or more than the third predetermined value, rounding by rounding off by a quantization operation is performed. The image signal processing method according to claim 5, wherein: 8. The encoding process according to claim 1, wherein the Huffman encoding is performed by rearranging the orthogonally-transformed data in ascending order of frequency components and combining a continuous number of zeros of data with non-zero data. Claim 5
8. The image signal processing method according to claim 7.