JPH06105165A - Image compression device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image compression apparatus capable of improving the display response of an image particularly when the compression rate is changed. A DCT data storage unit 32 for storing DCT conversion data, a switching unit 31 for switching whether or not the DCT conversion data output from the DCT conversion unit 11 is supplied to the DCT data storage unit 32, and a quantization unit 12. Input to D
A switching unit 33 that switches between the CT conversion unit 11 and the DCT data storage unit 32, and the inverse quantization unit 2
2 is input to the quantizer 12 and the entropy decoder 21.
And a switching unit 34 that switches from which of the two is supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image in which compressed data is obtained from an input image by orthogonal transformation, quantization and entropy coding, and a decoded image is generated from the compressed data by entropy decoding, dequantization and inverse orthogonal transformation. The present invention relates to a compression device, and particularly to improve a display response for evaluating the image quality after compression.

[0002]

2. Description of the Related Art An example of the configuration of a conventional image compression apparatus is shown in FIG. In the following description, JPEG (Joint Photographic Expert Gro), which is an international standard for still image compression as orthogonal transformation, is used.
The case where the discrete cosine transform (DCT) used in up) and the like is applied will be shown.

In FIG. 2, reference numeral 11 denotes a DCT transforming unit, which sequentially takes in block data obtained by dividing an input image into blocks of 8 × 8 pixels, and performs discrete cosine transform on the block data. Reference numeral 12 denotes a quantizer, which quantizes the data converted by the DCT converter according to a predetermined quantization table. Reference numeral 13 denotes an entropy coding unit, which is a quantization unit 12
The data quantized by is entropy-encoded according to an encoding table (not shown) such as Huffman encoding. Compressed data of the input image is obtained by each of these units, and the compressed data is stored in an external storage device such as a magnetic disk or transferred via a communication line.

Next, reference numeral 21 is an entropy decoding unit, which uses the same code as that used at the time of the entropy coding for compressed data read from an external storage device such as a magnetic disk or compressed data transferred via a communication line. Entropy decoding is performed using a conversion table (not shown). Two
Reference numeral 2 denotes an inverse quantization unit, which inversely quantizes the data decoded by the entropy decoding unit 21 using the same quantization table as in the above quantization. Reference numeral 23 denotes an IDCT conversion unit, which performs inverse discrete cosine transform (IDCT) on the data inversely quantized by the inverse quantization unit 22. This allows
A decoded image is generated from the supplied compressed data.

[0005]

By the way, when the conventional image compression apparatus having the above-mentioned configuration is used, the quantization table is variously changed in order to change the compression rate, and the image quality after compression at that time is visually evaluated. In such a case, it is necessary to input an image each time, perform DCT transformation, quantization, entropy coding, and perform entropy decoding, dequantization, and IDCT transformation on the obtained compressed data, so that many processes are performed each time. . Therefore, there is a problem that it takes time to display the result and the responsiveness is poor.

The present invention has been made under such a background, and an object thereof is to provide an image compression apparatus which can improve the display response of an image particularly when the compression rate is changed.

[0007]

In order to solve the above-mentioned problems, the present invention provides an orthogonal transform means for orthogonally transforming an input image and outputting orthogonal transform data, and a method for quantizing and quantizing the orthogonal transform data. Quantization means for outputting data, entropy coding means for entropy coding the quantized data and outputting entropy coded data, and entropy decoding for entropy decoding the entropy coded data and outputting entropy decoded data And a dequantization unit that dequantizes the entropy-decoded data and outputs the dequantized data, and an inverse orthogonal transformation unit that inversely orthogonally transforms the dequantized data to generate a decoded image. In the image compression apparatus, the orthogonal transform data storage means for storing the orthogonal transform data and the output from the orthogonal transform means are provided. First switching means for switching whether or not to supply the orthogonal transformation data to the orthogonal transformation data storage means, and which of the orthogonal transformation means and the orthogonal transformation data storage means supplies the input to the quantization means. And a third switching means for switching whether the input to the dequantization means is supplied from the quantization means or the entropy decoding means. .

[0008]

According to the present invention, the orthogonal transformation data storage means stores the orthogonal transformation data, and the first switching means supplies the orthogonal transformation data output from the orthogonal transformation means to the orthogonal transformation data storage means. The second switching means switches whether the input to the quantization means is supplied from the orthogonal transformation means or the orthogonal transformation data storage means, and the third switching means inputs to the inverse quantization means. Is switched between the quantizing means and the entropy decoding means. This makes it possible to read the already stored orthogonal transformation data from the orthogonal transformation data storage means and supply it to the quantization means without inputting the target image every time the quantization table is changed and performing orthogonal transformation. By directly supplying the quantized data to the dequantization means, unnecessary entropy coding and decoding in the quality evaluation of the compressed image can be omitted, so that the processing is significantly streamlined and the display response Higher speed is achieved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an image compression apparatus according to an embodiment of the present invention. In this figure, the same parts as those shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, reference numerals 31, 33 and 34 denote switching units. The switching unit 31 converts the DCT conversion data output from the DCT conversion unit 11 into the DCT data storage unit 32.
To supply or not. DCT data storage unit 3
Reference numeral 2 stores DCT conversion data input from the DCT conversion unit 11 via the switching unit 31. Further, the switching unit 33 switches whether the input to the quantization unit 12 is supplied from the DCT conversion unit 11 or the DCT data storage unit 32. Further, the switching unit 34 switches from which of the quantization unit 12 and the entropy decoding unit 21 the input to the dequantization unit 22 is supplied.

Next, the operation when an image is first input to the image compression apparatus having the above configuration will be described. First, the switching unit 31 is set to supply the DCT conversion data to the DCT data storage unit 32. This allows
The DCT conversion data output from the DCT conversion unit 11 is D
It is stored in the CT data storage unit 32.

Also, the switching unit 33 is a DCT conversion unit 1.
The DCT-transformed data output from 1 is set to be supplied to the quantization unit 12. As a result, the DCT conversion data is supplied from the DCT conversion unit 11 to the quantization unit 12 and quantized according to the quantization table. The quantized data thus obtained is supplied to the entropy coding unit 13 and entropy coded, and then stored as compressed data in an external storage device such as a magnetic disk or transferred through a communication line. To be done.

Further, when the switching unit 34 generates a decoded image using the stored (or transferred) compressed data, the switching unit 34 sends the entropy decoded data output from the entropy decoding unit 21 to the dequantization unit 22. Set to supply. On the other hand, when only evaluating the quality of the compressed image without storing the compressed data, the switching unit 34
Is set so that the quantized data output from the quantization unit 12 is directly supplied to the inverse quantization unit 22.

That is, when the quality of the compressed image is only evaluated and the storage of the compressed data is not involved, the quantized data is directly supplied from the quantization unit 12 to the dequantization unit 22, and the quantization It is inversely quantized according to the same quantization table as. Therefore, in this case, the entropy coding and decoding processes are omitted, and as a result, the display response can be speeded up.

Next, a case will be described in which the compression rate is changed for the same image using different quantization tables and the quality of the obtained compressed image is evaluated. In this case, since the same image is used, the DCT conversion data output from the DCT conversion unit 11 is always the same data regardless of the change of the compression rate. Further, as described above, when the image is first input, the DCT conversion data is stored in the DCT data storage unit 32. Therefore, the stored DCT conversion data can be used in the second and subsequent processes.

Therefore, the switching unit 31 is set so as not to supply the DCT conversion data to the DCT data storage unit 32 in the second and subsequent processes. Also, the switching unit 3
3 is a DCT read from the DCT data storage unit 32
The conversion data is set to be supplied to the quantizer 12.
As a result, the DCT conversion data is stored in the DCT data storage unit 3
2 is supplied to the quantizer 12 and is sequentially quantized according to the second, third, ... Quantization tables (not shown).
Therefore, it is possible to omit the input image capturing process and the DCT conversion process for the second and subsequent processes.

Furthermore, the switching unit 34 is set to supply the quantized data output from the quantizing unit 12 to the inverse quantizing unit 22, since it is only necessary to evaluate the quality of the compressed image. As a result, the quantized data is directly supplied from the quantizing unit 12 to the dequantizing unit 22 and is sequentially dequantized in accordance with the same second, third, ... . Then, these inversely quantized data are sequentially subjected to inverse discrete cosine transform by the IDCT transforming section 23 to generate a decoded image in which the compression rate is changed. That is, also in this case, the entropy encoding and decoding processes are omitted, and the speed is increased.

The storage capacity of the DCT data storage unit 32 does not have to be a size capable of storing the entire image to be converted, and may be any size sufficient to store a partial image for quality evaluation. Good.

[0019]

As described above, according to the present invention, when an image is obtained when the compression rate of the same image is changed, the same image is input and DCT transform, entropy coding and decoding are performed each time. Since there is no need to
The display response can be speeded up. As a result, work such as obtaining the optimum value of the compression ratio of the recorded image can be efficiently advanced. Further, it is possible to provide an image compression device having a good man-machine interface with excellent display responsiveness.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image compression apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of a conventional image compression device.

[Explanation of symbols]

11 ... DCT transformation unit, 12 ... Quantization unit, 13 ... Entropy coding unit, 21 ... Entropy decoding unit,
22 ... Inverse quantization unit, 23 ... IDCT conversion unit, 31,
33, 34 ... Switching unit, 32 ... DCT data storage unit

Claims (1)

[Claims] 1. An orthogonal transform means for orthogonally transforming an input image and outputting orthogonal transform data, a quantizing means for quantizing the orthogonal transform data and outputting quantized data, and an entropy coding for the quantized data. , Entropy coding means for outputting entropy coded data, and entropy decoding the entropy coded data,
Entropy decoding means for outputting entropy-decoded data, dequantization means for dequantizing the entropy-decoding data and outputting dequantized data, and inverse-orthogonal transform of the dequantized data for decoding a decoded image. In an image compression apparatus having an inverse orthogonal transform means for generating, an orthogonal transform data storage means for storing the orthogonal transform data, and orthogonal transform data output from the orthogonal transform means to the orthogonal transform data storage means. First switching means for switching whether or not to supply, second switching means for switching whether the input to the quantization means is supplied from the orthogonal transformation means or the orthogonal transformation data storage means, and the reverse A third switching means for switching whether the input to the quantizing means is supplied from the quantizing means or the entropy decoding means. Image compression apparatus characterized by.