JPH0691615B2 - Image signal encoding device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image signal data compression encoding apparatus in which a user can select a compression method after confirming the image quality of a reproduced image after data compression. .

[Conventional technology and its problems]

The data compression method of the image signal is roughly divided into an information amount storage type compression method capable of completely reproducing the original image and a non-information amount compression method in which the reproduced image after compression / expansion causes some deterioration with respect to the original image. There is a storage type compression method, but in general, in order to perform data compression at a high compression rate for a multi-valued image in which one pixel is expressed in many levels (for example, 8bit 256 levels, etc.), a non-information type Used. In this information amount non-storing type data compression method, the compression rate is increased by partially degrading the image quality. Therefore, the image quality is degraded as the compression rate is increased. When compressing and transmitting or storing an image, there is a demand to use a data compression method with a maximum compression ratio due to deterioration within an allowable range. Especially when medical images such as X-rays are targeted for compression, is the degree of image quality deterioration due to the data pressure lines determined whether the reproduced image after data compression can be used for diagnosis using the image or for recording the affected area? It becomes a major factor in deciding whether or not it is important to select a compression method that ensures image quality above the standard. However, even if the same data compression method is used, the degree of deterioration of the reproduced image greatly differs depending on the input image. For this reason, in the conventional encoding method, a compression method with a low compression rate is used to maintain the image quality above the standard even in the worst case, but be prepared that some images will be below the standard image quality. A compression method was set so that an average image could maintain image quality above the standard. The former case has a drawback that a sufficient compression ratio cannot be obtained, and the latter case lacks reliability of a reproduced image by data compression, which is a fatal problem particularly for medical images.

[Object of the Invention]

The object of the present invention is that the user can visually confirm the reproduced image after data compression while switching the compression method, and can easily select the compression method that realizes the highest compression rate with the image quality within the allowable range. An object is to provide an image signal encoding method and an encoding device.

[Structure of Invention]

An image signal encoding apparatus according to the present invention includes a unit for generating a plurality of reproduced images corresponding to a plurality of compression ratios by changing a compression parameter, a unit for displaying the plurality of reproduced images, and a unit for reproducing the plurality of reproduced images. Means for compressing an original image using a compression parameter corresponding to a reproduced image selected from an image to generate compressed data; and encoding the compressed data using a code predetermined by the compression parameter to generate encoded data. It is provided with a means for generating and a means for outputting the compression parameter corresponding to the reproduction image selected from the plurality of reproduction images and the encoded data obtained by using the compression parameter. .

〔Example〕

Next, the image signal device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The control unit 4 controls the entire operation according to the control signal A. First, the compression / reproduction unit 1 compresses / expands the image signal X using the specified compression parameter P by switching and specifying the compression parameter P corresponding to a plurality of compression ratios as the control signal A. Generate an image signal X ′,
The display unit 2 displays the reproduced image. By displaying a plurality of reproduced images reproduced while switching the compression parameter P, visually judging from these reproduced images, selecting one reproduced image and instructing the control unit to correspond to the selected reproduced image. The original image is compressed using the compression parameter, and the encoded data C that has been encoded is output together with the compression parameter P used for the compression. The process of compressing the image signal X of the original image using the designated compression parameter P is performed by the compression / reproduction unit 1 to generate the compressed data D. The encoding unit 3 encodes the compressed data D using a code determined in advance by the compression parameter P to generate encoded data C.

Although a plurality of procedures can be considered as a procedure for controlling the flow of the entire processing, three typical procedures are shown below.

(A) At the stage of displaying the reproduced image, the compression / reproduction unit 1 uses the designated compression parameter P to generate the reproduced image signal X ′ from the image signal X, and the display unit 2 displays the reproduced image. When one is selected from a plurality of reproduced images, the compression / reproduction unit 1 outputs the image signal X to the selected reproduced image X ′.
Data is compressed using the compression parameter P corresponding to, and the compressed data D that has been compressed is encoded by the encoding unit 3 to generate encoded data C.

(B) At the stage of displaying the reproduced image, the compression / reproduction unit 1 data-compresses the image signal X using the designated compression parameter P, stores the data inside, and generates and displays the corresponding reproduced image. Displayed in Part 2. When one is selected from a plurality of reproduced images, the one using the compression parameter P corresponding to the selected reproduced image is read from the plurality of compressed data P stored in the compression / reproduction unit 1. It is output and encoded by the encoding unit 3.

(C) At the stage of displaying the reproduced image, the compression / reproduction unit 1
Compresses the image signal X using the designated compression parameter P, passes the compressed data D to the encoding unit 3 and generates a corresponding reproduced image to display on the display unit 2.
The encoding unit 3 encodes the compressed data D received from the compression / reproduction unit 1 and stores the encoded data C inside. When one is selected from the plurality of reproduced images, the compression / encoding is performed using the compression parameter P corresponding to the selected reproduced image from the plurality of encoded data C stored in the encoding unit 3. The encoded data C thus converted is read out and output.

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

FIG. 2 is a block diagram showing an embodiment of the coding apparatus of the present invention using the procedure of (a) above. Input signals to the control unit 21 include a compression parameter selection signal S and a mode switching signal M, which can be arbitrarily set 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 the display mode and the coding mode. The control unit 21 controls the operation of the entire coding apparatus by the input signals as follows. In the case of the display mode, the reproduced image obtained by compressing the image signal X with the selected compression parameter is displayed on the display unit 24, and in the case of the encoding mode, one image visually selected from a plurality of reproduced images is displayed. The original image is compressed with the compression parameter corresponding to the reproduced image, and the encoded data that has been encoded is output together with the compression parameter used for compression.

The case of the display mode will be described first. In the compression unit 22, the image signal X is data-compressed using the compression parameter P (parameter selected by the compression parameter selection signal S) designated by the control unit, and the compressed data D is output. As an example of data compression, DCT (Discrete Cos
FIG. 3 shows the configuration of the compression unit when orthogonal transform coding such as ine Transform) is used, and FIG. 4 shows the configuration of the compression unit when predictive coding is used. The compression unit adopting the orthogonal transform coding method of FIG. 3 is composed of an orthogonal transformer 31 and a quantizer 32. The image signal X is converted into transform coefficients by the orthogonal transformer 31, the transform coefficients are quantized by the quantizer 32, and the quantized coefficients are output as the compressed data D. In this compression unit, the compression rate is mainly determined by the number of quantization bits of the quantizer 32 (the number of bits after quantization) and the quantization characteristics (linear quantization, non-linear quantization, etc.), so it is specified by the control unit. The number of quantization bits and the quantization characteristic are used as the compression parameter P. The compression unit adopting the predictive coding system of FIG. 4 is composed of a predictor 42, a quantizer 41, a subtraction circuit 43, and an addition circuit 44. Image signal X and predictor 42
The prediction error value which is the difference component from the prediction value output from is subtracted by the subtraction circuit 43, quantized by the quantizer 41, and the quantized prediction error value is output as the compressed data D. In the adder circuit 44, the quantized prediction error value is added to the prediction value to obtain the locally decoded signal, and this signal is used in the predictor 42 to obtain the prediction value. Also in the compression unit in this predictive coding, the quantizer 41 is used as the compression parameter P as in the compression unit in the orthogonal transform coding.
The number of quantization bits and the quantization characteristics of are used.

The compressed data D obtained as described above is decompressed by the decompression unit 23 in FIG. 2 to generate the reproduced image signal X '. This reproduced image signal X'is output and displayed on the display unit 24 such as a display or a hard copy.

The decompression unit in the orthogonal transform coding is composed of an orthogonal inverse transformer, and the reproduced image signal X ′ is generated from the compressed data D (quantized transform coefficient). As shown in FIG. 5, the decompression unit in the predictive coding includes a prediction unit 61 and an addition circuit 62, and a reproduced image signal X'is generated from the compressed data D (quantized prediction error value). The predictor 61 and the adder circuit 62 are the same as the predictor 42 and the adder circuit 44 in FIG. In the case of predictive coding, since the reproduced image signal has already been obtained as the local decoded signal at the output of the addition circuit 44 in the compression unit shown in FIG. 4, this signal is directly extracted and input to the display unit 24. Second by using as
The extension part of the figure is unnecessary.

In the display mode, as described above, the error image and the reproduced image when compressed at different compression ratios are displayed by changing the compression parameter P by switching the compression parameter selection signal S and displayed on the display unit. By using this display mode, the user can maintain the image quality within the allowable range and find the compression parameter 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 reproduced image selected in the display mode to maintain the image quality within the allowable range. Images can be encoded and transmitted or stored with high compression efficiency.

When the encoding mode is selected in FIG. 2, the compression unit 22
A code word is assigned to the compressed data D, which is the output of, by 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 selectable compression parameter so that the compression rate is statistically highest, and the compression selected at the time of encoding. Codewords are assigned using a table corresponding to the parameters. A code corresponding to the compression parameter used for compression is added to the encoded data C thus obtained by the parameter addition unit 26, and the encoded data C is output to the transmission line or the storage device.

If the compression parameter selection signal S has already been set to the compression parameter to be encoded in the display mode, the compression encoding is executed using this parameter only by switching the mode to the encoding mode.

Some of the embodiments of the encoding apparatus described above use the control procedure (a) described above, but the embodiments using the procedures of (b) and (c) also include the compression unit 22 or the encoding. This can be realized by adding a memory that stores compressed data or encoded data to the unit 25 and partially changing the control procedure of the control unit 21. Next, the configuration of the decoding device for decoding the encoded data encoded by the encoding device of the present invention will be described with reference to the block diagram of FIG. The code received from the transmission path or the storage device is separated by the parameter separation unit 71 into the coded data C of the image and the code indicating the selected compression parameter P, and passed to the decoding unit 72. Similar to the encoding unit 25 of the encoding device, the decoding unit 72 has a correspondence table of code words and compressed data determined for each compression parameter, and a table corresponding to the compression parameter P separated by the parameter separation unit. Is used to decode the code word C 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 in the predictive encoding is the fifth.
It is the same as shown in the figure.

〔The invention's effect〕

As described above, by using the image signal encoding device of the present invention, the user can confirm the reproduced image after data compression while switching the compression parameter corresponding to the compression rate of a plurality of steps, and the allowable range. The image signal can be compression-encoded by using the compression parameter that realizes the highest compression rate while maintaining the image quality inside and output to the transmission line or the storage device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of an embodiment of an encoding device of the present invention,
FIG. 3 is a block diagram showing an example of the configuration of the compression section in FIG. 2 in orthogonal transform coding, and FIG. 4 is a block diagram showing an example of the configuration of the compression section in FIG. 2 in predictive coding, 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. 1 ... compression / playback unit, 2 ... display unit, 3 ... encoding unit,
4 ... control unit, 21 ... control unit, 22 ... compression unit, 23 ... decompression unit, 24 ... display unit, 25 ... encoding unit, 26 ... parameter addition unit, 31 ... orthogonal transformation unit , 32 …… Quantizer, 41 ……
Quantizer, 42 ... Predictor, 43 ... Subtraction circuit, 44 ... Addition circuit, 61 ... Predictor, 62 ... Addition circuit, 71 ... Parameter separation unit, 72 ... Decoding unit, 73 ... … Extension part.

Claims (1)

[Claims] 1. A means for generating a plurality of reproduced images corresponding to a plurality of compression ratios by changing a compression parameter,
A unit for displaying the plurality of reproduced images, a unit for compressing an original image by using a compression parameter corresponding to a reproduced image selected from the plurality of reproduced images to generate compressed data, and a unit for compressing the compressed data by the compression parameter. Means for generating encoded data by encoding using a predetermined code, the compression parameter corresponding to the reproduction image selected from the plurality of reproduction images, and the encoding obtained using the compression parameter And a means for outputting data and an image signal encoding apparatus.