JP2000004437A - Picture coder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the compression rate without switching quantity tables. SOLUTION: An LPF 11 that attenuates a high frequency component of received image data is provided to a pre-stage of the picture coder consisting of a DCT section 1, a quantization section 2 and a coding section 3. The received image data or image data that are an output of the LPF 11 are selectively fed to the picture coder via a switch 12. Then a control section 13 controls the selection of the switch 12 depending on depth information in the received image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding apparatus for encoding image data with high efficiency.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional image encoding device and image decoding device. When encoding is performed by an image encoding device, image data is usually divided into 8 × 8 blocks and input to the image encoding device. In FIG. 3, a video signal (image data) divided into blocks is frequency-decomposed by a discrete cosine transform (DCT) unit 1,
Input to the quantization unit 2. The quantization unit 2 quantizes the output of the DCT unit 1 with reference to a weighting table set for each frequency.

The output of the quantization unit 2 is input to the encoding unit 3. The encoding unit 3 encodes the output of the quantization unit 2 with reference to a table created based on the appearance frequency of the output value. The image data encoded in this way is transmitted or stored by the transmission or storage unit 4.

On the other hand, an image decoding device decodes image data by a procedure reverse to that of an image encoding device. Image data from the transmission or storage unit 4 is input to the decoding unit 5. The decoding unit 5 decodes the image data with reference to the table created based on the appearance frequency. The output of the decoding unit 5 is input to the inverse quantization unit 6. Inverse quantization unit 6
Dequantizes the output of the decoding unit 5 with reference to the weighting table. The output of the inverse quantization unit 6 is an inverse DCT unit 7
Is input to The inverse DCT unit 7 performs an inverse DCT on each block, and restores and outputs image data (video signal).

In the image coding apparatus having the above-described configuration, parameters for controlling the compression ratio of image data are two types of tables used in the quantization unit 2 and the coding unit 3. Here, an example of a table used in the quantization unit 2 will be described. The quantization table shown in FIG. 4 corresponds to an 8 × 8 block.
This specifies the quantization width of the value of the CT operation result. As shown in FIG. 4, the higher the frequency in both the horizontal and vertical directions, the wider the quantization width is, and the compression ratio is increased by intentionally reducing the high frequency accuracy.

FIG. 5 shows a quantization table in which the quantization width in the higher frequency band is made wider than that in FIG. 4, and the compression rate is higher in the quantization using the table in FIG. If the compression ratio is increased, deterioration due to quantization is conspicuous, and the quality of the video is reduced.

[0007]

By the way, in order to increase the compression ratio or, conversely, to further enhance the quality of the video, the quantization table in the quantization unit 2 is switched according to the degree of the high frequency included in the video. It is possible. However, if the quantization table is switched, the table must be transmitted or stored for each block, which may result in a reduction in the compression ratio.
Not preferred.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and has as its object to provide an image coding apparatus capable of increasing a compression ratio without switching a quantization table.

[0009]

According to the present invention, in order to solve the above-mentioned problems of the prior art, an image encoding apparatus for encoding input image data is provided at a stage preceding the image encoding apparatus. A low-pass filter (11) for attenuating a high-frequency component of the input image data; and selectively supplying the input image data and the image data output from the low-pass filter to the image encoding device. An image encoding apparatus comprising: a switch (12); and a control unit (13) that controls selection of the switch according to depth information of the input image data. It is.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image coding apparatus according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the image encoding device of the present invention, and FIG. 2 is a diagram for explaining the operation of the image encoding device of the present invention. In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, a video signal (image data) divided into blocks is supplied to a low-pass filter (LPF) 11.
And one terminal of the switch 12. The video signal is a signal to be compressed, such as the luminance signal Y and the color difference signals Pb and Pr. The output of LPF11 is switch 1
2 is input to the other terminal.

The above-described depth information of the video signal, which will be described in detail later, is input to the control unit 13. As shown in FIG. 2, the control unit 13 sets the value of the input depth information to a predetermined threshold value T.
If it is larger than the threshold value T, it is determined to be the background. The control signal from the control unit 13 is, for example, a binary signal representing 1 when it is a background and 0 when it is not a background.
2 is input.

When the control signal from the control unit 13 is 1, that is, in the background portion on the screen, the switch 12
Is selected, and when the control signal from the control unit 13 is 0, that is, in a portion other than the background on the screen, the switch 12
Selects the input video signal. As described above, the present invention is characterized in that the LPF 11 attenuates the high frequency components of the background portion of the screen of the input video signal.

The output of the switch 12 is input to the DCT unit 1, frequency-decomposed, and input to the quantization unit 2. The quantization unit 2 quantizes the output of the DCT unit 1 with reference to a weighting table set for each frequency. The output of the quantization unit 2 is input to the encoding unit 3. The encoding unit 3 encodes the output of the quantization unit 2 with reference to a table created based on the appearance frequency of the output value. The image data encoded in this manner is transmitted or stored by a transmission or storage unit 4 not shown. DC
The operations from the T unit 1 to the encoding unit 3 are the same as those in the related art, and in the present invention, the above processing is performed on the image data input to the DCT unit 1.

Here, the depth information of the video signal will be described. There are various methods for obtaining depth information of a video signal. For example, as described in JP-A-8-331607, depth information of a video signal can be obtained by detecting motion of a video. . The part without motion can be determined to be the background.

As described above, according to the present invention, it is assumed that the portion in front of the background is more important than the background in the video on the screen, and the high-frequency component of the background portion is attenuated. Increase compression ratio. This makes it possible to increase the compression ratio without switching the quantization table. Note that, when encoding is performed by the image encoding device of the present invention, the image decoding device has no influence.

[0017]

As described in detail above, the image coding apparatus according to the present invention is provided in the preceding stage of the image coding apparatus, and a low-pass filter for attenuating the high frequency component of the input image data, A switch for selectively supplying the image data output from the low-pass filter and the image data output from the low-pass filter to the image encoding device, and a control unit for controlling selection of the switch according to depth information of the input image data. With this configuration, the compression ratio can be increased without switching the quantization table.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a diagram illustrating an example of a quantization table.

FIG. 5 is a diagram showing another example of the quantization table.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discrete cosine transformation part 2 Quantization part 3 Encoding part 11 Low pass filter 12 Switch 13 Control part

Claims (1)

[Claims] 1. An image coding apparatus for coding input image data, comprising: a low-pass filter provided before the image coding apparatus and attenuating a high-frequency component of the input image data; A switch that selectively supplies the input image data and the image data output from the low-pass filter to the image encoding device, and controls selection of the switch according to depth information of the input image data. An image encoding device, comprising: a control unit.