JPS6257367A - Method and apparatus for coding picture signal - Google Patents

Abstract

PURPOSE:To confirm an error picture after data compression while the user selects a compression parameter corresponding to plural steps of compression rates by outputting the compression parameter and a coded data corresponding to an error picture selected by visual discrimination from plural error pictures. CONSTITUTION:A compression/reproduction section 1 generates a reproduced picture signal X' obtained from a picture signal X with the compression parameter P by designating switchingly the compression parameter P corresponding to plural steps of compression rates as a control signal A, an error picture generating section 5 generates an error picture Y comprising a difference component between the reproduced picture signal X' and the original picture signal X and a display section 2 displays the error picture. While the compression parameter P is being selected, the plural reproduced error pictures are displayed, one error picture is selected by the visual discrimination from the error picture and a command is given to a control section so as to compress the original picture which the compression parameter corresponding to the selected error picture is used, and the coded data C is outputted together with the compression parameter P used for the compression.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a data compression encoding method for image signals, in which a user can select a compression method after confirming the image quality of a reproduced image after data compression; Regarding equipment.

[Conventional technology and its problems]

Data compression methods for image signals can be broadly divided into information-preserving compression methods that can completely reproduce the original image, and information-preserving compression methods that allow the reproduced image after compression/expansion to be degraded in some way compared to the original image. There is a preservation type compression method, but a non-information preservation type is generally used to compress data at a high compression rate for multivalued images in which one pixel is expressed at many levels (for example, 8 bits, 256 levels, etc.). It will be done. In this data compression method that does not preserve the amount of information, the compression rate is increased by partially degrading the image quality, so as the compression rate increases, the image quality deteriorates. When compressing images and transmitting or storing them, there is a demand for using a data compression method that has the highest compression rate possible while keeping deterioration within an acceptable range. In particular, when compressing medical images such as X-rays, the degree of image quality deterioration due to data compression is determined by whether the reproduced image after data compression can be used for diagnosis using the image or as a record of the affected area. It is important to select a compression method that ensures image quality that exceeds the standard. However, even if the same data compression method is used, the degree of deterioration of the reproduced image varies greatly depending on the input image. For this reason, with conventional encoding methods, you must either use a compression method that keeps the compression rate low to maintain image quality above the standard even in the worst case, or be prepared for the image quality of some images to be below the standard. The compression method was set so that the average image could maintain image quality above the standard. The former case has the disadvantage that a sufficient compression rate cannot be obtained, and the latter case lacks reliability of reproduced images due to data compression, which is a fatal problem especially for medical images.

[Purpose of the invention]

The purpose of the present invention is to enable the user to visually check the error image consisting of the difference component between the reproduced image after data compression and the original image while switching the compression method, and to achieve the highest compression rate with image quality within the allowable range. An object of the present invention is to provide a method and apparatus for encoding an image signal, which can easily select a compression method. By looking at the error image, it is possible to accurately judge the degree of image quality deterioration due to compression/expansion.

[Structure of the invention]

The image signal encoding method of the present invention displays error images between the reproduced image and the original image corresponding to multiple compression ratios by changing compression parameters, and allows visual judgment to be made from at least a plurality of error images. By selecting one, the original image is compressed using the compression parameter corresponding to the selected error image, and the encoded data encoded using the code determined in advance by the compression parameter is used for compression. It is characterized by outputting the compression parameters.

Further, the encoding device of the present invention includes means for generating a reproduced image corresponding to a plurality of compression ratios by changing compression parameters, means for generating an error image between the reproduced image and the original image, and a means for generating an error image between the reproduced image and the original image. means for displaying a compressed image; means for compressing an original image using the specified compression parameters to generate compressed data; and encoding the compressed data using a code predetermined by the compression parameters to generate encoded data. a compression parameter corresponding to the selected error image by selecting one from at least a plurality of error images by visual judgment; and the encoding obtained using the compression parameter. The present invention is characterized by comprising a means for outputting data.

〔Example〕

Next, the image signal encoding method and encoding apparatus of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Control unit 4 controls the overall operation according to control signal A. First, by switching and specifying compression parameters P corresponding to multiple levels of compression ratios as control signal A, compression/reproduction section 1 compresses and expands image signal X using the specified compression parameters P. generate a reproduced image signal X';
The error image generation section 5 generates an error image Y consisting of the difference component between the reproduced image signal X' and the original image signal X, and the display section 2 displays this error image. While changing the compression parameter P, display a plurality of reproduced error images, visually judge from these error images, select one error image, and instruct the control unit to correspond to the selected error image. The original image is compressed using the compression parameters, and encoded data C is output together with the compression parameters P used for compression. The process of compressing the image signal X of the original image using the specified compression parameter P is performed in the compression/reproduction unit 1, and compressed data D is generated. In the encoding unit 3, the compressed data D is set in advance by a compression parameter P.
The encoded data C is generated by encoding using the code defined by the above. Note that since the reproduced image generated by the compression/reproduction unit 1 can also be displayed on the display unit, appropriate compression parameters can be selected from both the reproduced image and the error image.

Although there are several possible procedures for controlling the overall processing flow, three representative procedures are shown below.

(a) At the stage of displaying the error image, the compression/reproduction unit 1
generates a reproduced image signal X' from the image signal indicate. When one of the plurality of error images is selected, the compression/reproduction unit 1 compresses the image signal X using the compression parameter P corresponding to the selected error image ff1Y, and the compressed data D is The encoder 3 encodes the data to generate encoded data.

(L)) At the stage of displaying the error image, the image signal The error image generation section generates an error image and displays it on the display section 2.

When one of the plurality of error images is selected, it is selected from among the plurality of compressed data P stored in the compression/reproduction unit 1.
The image using the compression parameter P corresponding to the selected error image is read out and encoded by the encoding unit 3.

(C) At the stage of displaying the error image, the compression/reproduction unit 1 data-compresses the image signal X using the specified compression parameter P, passes the compressed data P to the encoding unit 3, and displays the corresponding reproduction image is generated and passed to the error image generation section 5. The error image generated by the error image generation section 5 is displayed on the display section 2.

Further, the encoding section 3 encodes the compressed data D received from the compressed and reproduced section 1, and stores this encoded data C internally. When one of the plurality of error images is selected, the compression parameter P corresponding to the selected error image is selected from among the plurality of encoded data C accumulated in the encoding unit 3.
The encoded data C that has been compressed and encoded using is read out and output.

Next, an encoding apparatus using procedure (a) of these three control procedures will be described in detail.

FIG. 2 is a block diagram showing an embodiment of the encoding device of the present invention using the procedure (a) above. The input signals to the control unit 21 include a compression parameter selection signal S and a mode switching signal M.
is available and can be set arbitrarily by the user. The compression parameter selection signal S is a signal for selecting one compression parameter from a plurality of compression parameters corresponding to a plurality of compression ratios, and the mode switching signal M is a signal for switching between a display mode and an encoding mode. The control unit 21 controls the operation of the entire encoding device in the following manner using these input signals.

In the display mode, the error image when the image signal The original image is compressed using compression parameters corresponding to the error image, and the encoded data is output together with the compression parameters used for compression. Since both the reproduced image and the error image can be displayed on the display section 24, appropriate compression parameters can be determined from both images.

First, the case of display mode will be explained. In the compression section 22, the image signal X is compressed using the compression parameter P specified by the control section (the parameter selected by the compression parameter selection signal S), and compressed data D is output. An example of data compression is DCT (Di
Screte Cosige Trans-form
) etc. is shown in FIG. 3, and FIG. 4 shows the structure of the compression section in the case of predictive coding. The compression section employing the orthogonal transform encoding method shown in FIG. 3 is composed of an orthogonal transformer 31 and a quantizer 32. The image signal X is converted into transform coefficients by an orthogonal transformer 31, the transform coefficients are quantized by a quantizer 32,
The quantized coefficients are output as compressed data D, and the compression rate in this compression section is mainly determined by the number of quantization bits of the quantizer 32 (the number of bits after quantization) and the quantization characteristics (such as deliberate quantization and nonlinear The number of quantization bits and the quantization characteristics are used as the compression parameter P designated by the control unit. The compression unit employing the predictive encoding method shown in FIG. 4 is the predictor 42. Quantizer 41. A prediction error value, which is a difference component between the 0 image signal X configured by a subtraction circuit 43 and an addition circuit 44, and the predicted value Then, a quantized prediction error value is output as compressed data D. In the adding circuit 44, the quantized prediction error value is added to the predicted value X to obtain a locally decoded signal, and this signal is used in the predictor 42 to obtain the predicted value. In the compression unit in predictive encoding, the number of quantization bits and quantization characteristics of the quantizer 41 are used as compression parameters, similarly to the compression unit in orthogonal transform encoding.

The compressed data D obtained as described above is expanded by the expansion section 23 shown in FIG. 2 to generate a reproduced image signal X'. Further, an error image signal Y consisting of a difference component between the reproduced image signal X and the original image signal X is generated by the error image generation section 27. This error image signal Y is output to and displayed on a display section 24 such as a display or a hard copy.
The reproduced image signal X' can also be displayed. The decompression unit in orthogonal transform encoding is constituted by an orthogonal inverse transformer 51, and a reproduced image signal X' is generated from compressed data D (quantized transform coefficients). As shown in FIG. 5, the decompression section in predictive encoding is composed of a prediction section 61 and an adder 1 circuit 62, and generates a reproduced image signal X' from compressed data D (quantized prediction error value). This predictor 61. Addition circuit 6
2 is the predictor 42 in FIG. It is the same as the adder circuit 44. In the case of predictive encoding, since the reproduced image signal has already been obtained as a locally decoded signal at the output of the adder circuit 44 in the compression section shown in FIG. , By using it as a force, the extension part shown in Figure 2 becomes unnecessary. The configuration of the error image generation section 27 is to simply use a subtraction circuit to calculate X' and
The difference between both signals may be calculated and set as Y, or the result of filtering this difference component may be set as Y to make it easier to see the error.

In the display mode, as explained above, by switching the compression parameter selection signal S and changing the compression parameter P, the error image and the reproduced image when compressed at different compression ratios are displayed on the display section. By using this display mode, the user can maintain image quality within an acceptable range and find compression parameters with the highest compression efficiency.

Next, the user sets the mode switching signal to the encoding mode, and sets the compression parameter selection signal S to the compression parameter corresponding to the error image selected in the display mode, thereby maintaining the image quality within the allowable range and achieving maximum compression. Images can be encoded and transmitted or stored in a highly efficient manner.

In FIG. 2, when the encoding mode is selected, the compression unit 2
The compressed data D, which is the output of step 2, is assigned a code word in the encoding unit 25 and converted into encoded data C. The correspondence table between each value of the compressed data D and the code word is determined in advance using a test image for each preselectable compression parameter so that the compression rate is statistically the highest, and when encoding A table corresponding to the compression parameters is used and allocated. The coded data C obtained in this manner is added with a code corresponding to the compression parameter used for compression in the parameter adding section 26, and is output to a transmission path or storage device.

Note that if the compression parameter selection signal S has already been set as the compression parameter to be encoded in the display mode, compression encoding can be realized by simply switching the mode to the encoding mode using this parameter.

The embodiment of the encoding device described above uses the previously explained control procedure (a), but the embodiment using the procedures (b) and (C) also uses the compression unit 22 or the encoding device. Part 2
This can be realized by simply adding a memory for storing compressed data or encoded data to 5 and partially changing the control procedure of the control unit 21.

Next, the configuration of a decoding device that decodes encoded data encoded by the encoding device of the present invention will be explained using the block diagram of FIG. 6. The code received from the transmission path or the storage device is separated by a parameter separation unit 71 into encoded image data C and a code indicating the selected compression parameter P, and then passed to a decoding unit 72. Like the encoding unit 25 of the encoding device, has a correspondence table between code words and compressed data determined for each compression parameter, and by using the table corresponding to the compression parameter P separated by the parameter separation unit, The code word C is decoded into the original compressed data D. The decompression unit 73 decompresses the compressed data D to generate a reproduced image signal X'.

The decompression unit 73 is the same as the decompression unit 23 in the encoding device, and the configuration for predictive encoding is the same as that shown in FIG.

〔Effect of the invention〕

As described above, by using the image signal encoding method and encoding device of the present invention, the user can check the error image after data compression while switching the compression parameters corresponding to the compression ratio of multiple steps. The image signal can be compressed and encoded using compression parameters that achieve the highest compression rate while maintaining image quality within an acceptable range, and output to a transmission path or storage device. By looking at the error image, it is possible to accurately judge the degree of compression/expansion, which is difficult to judge from the reproduced image alone.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of an embodiment of the encoding device of the present invention,
FIG. 3 is a block diagram showing an example of the configuration of the compression unit in FIG. 2 in orthogonal transform encoding, and FIG. 4 is a block diagram showing an example of the configuration of the compression unit in FIG. 2 in predictive encoding. FIG. 5 is a block diagram showing an example of the configuration of the decompression unit in FIG. 2 in predictive encoding, and FIG. 6 is a block diagram showing an example of the configuration of a decoding device corresponding to the encoding device of the present invention. DESCRIPTION OF SYMBOLS 1... Compression/reproduction part, 2... Display part, 3... Encoding part, 4... Control part, 5... Error image generation part, 21
...control section, 22...compression section, 23...expansion section,
24... Display section, 25... Encoding section, 26... Parameter addition section, 27... Error image generation section, 31...
- Orthogonal transformer, 32... quantizer, 41... quantizer, 42... predictor, 43... subtraction circuit, 44...
- Addition circuit, 61...Predictor, 62...Addition circuit,
71... Parameter separation unit, 72... Decoding unit, 7
3...Extension part. Kaya 1 Figure 2vM Bud 3 Concave Buddha 4 Figure t

Claims (2)

[Claims] (1) Display error images between the reproduced image and the original image corresponding to multiple levels of compression ratio by changing the compression parameters,
By visually selecting one of at least a plurality of error images, the original image is compressed using a compression parameter corresponding to the selected error image, and a code determined in advance by the compression parameter is compressed. 1. A method for encoding an image signal, the method comprising: outputting encoded data encoded using the encoded data and the compression parameters used for compression. (2) means for generating a reproduced image corresponding to multiple levels of compression ratio by changing compression parameters; means for generating an error image between the reproduced image and the original image; and means for displaying the generated image. a means for compressing an original image to generate compressed data using the specified compression parameter; a means for encoding the compressed data using a code predetermined by the compression parameter to generate encoded data; 1 based on visual judgment from at least a plurality of error images.
encoding of an image signal, comprising: means for outputting the compression parameter corresponding to the selected error image and the encoded data obtained using the compression parameter by selecting one of the selected error images; Device.