JPH02164188A - High efficient coding device - Google Patents

Abstract

PURPOSE:To decrease the distortion of a part with a high brightness by increasing bit number assigned to the part with a high brightness in comparison with a bit number assigned to the part with a low brightness in the case of compressing a digital video signal. CONSTITUTION:A maximum value MAX for each block is detected from a picture element data PD of a digital video signal SDV supplied to a maximum value detection circuit 3. A minimum value MIN is detected from a picture element data PD of the digital video signal SDV supplied to a minimum value detection circuit 4 for each block. The minimum value MIN is subtracted from the maximum value MAX at a subtractor circuit 7 to form a dynamic range DR. The bit number assigned to a block is increased as the maximum value MAX in the block in a bit assignment table TB is increased and quantization is applied in an interval of a finner quantization step. On the other hand, as the maximum value MAX in the block is smaller, the assigned bit number to the block is reduced and quantization is applied in a coarse quantization step interval.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a high-efficiency encoding device, particularly a high-efficiency encoder suitable for compressing and transmitting the amount of data of a digital video signal subjected to gamma correction. related to conversion equipment.

[Summary of the invention]

The present invention provides a high-efficiency encoding device that compresses the amount of data of a digital video signal that has been subjected to gamma correction.
Compression of digital video signals is achieved by compressing the image data in areas with large brightness values, by increasing the number of bits allocated to areas with high brightness values compared to the number of bits allocated to areas with low brightness values. Distortion can be reduced to make it less noticeable on a cathode ray tube, and the amount of data can be further compressed in areas with small luminance values.

[Prior Art] As described in Japanese Patent Application No. 59-266407, the applicant of the present application determined the dynamic range of a plurality of pixels included in a two-dimensional block, and performed encoding adapted to this dynamic range. We have proposed a high-efficiency encoding device that performs this. Furthermore, as described in Japanese Patent Application No. 60-232789, a high-efficiency encoding device performs encoding adapted to a dynamic range with respect to a three-dimensional block formed from pixels in areas included in each of a plurality of frames. is proposed. Furthermore, as described in Japanese Patent Application No. 60-268817, there is a variable length encoding method in which the number of bits changes depending on the dynamic range so that the maximum distortion caused when quantization is constant. is proposed.

High-efficiency encoding system adapted to the above-mentioned dynamic range!
(referred to as ADRC) is suitable for application to digital television signals because it can significantly compress the amount of data to be transmitted. In particular, variable length ADRC can increase the compression rate.

[Problem to be solved by the invention]

By the way, the CRT of a television is C in Figure 6.
It has the light emission output characteristics shown in B.

In order to correct this, in the television camera, gamma correction is applied in advance so that the television signal becomes the state shown at CC in FIG.

Therefore, when compressing the image data of a television signal by the above-mentioned ADRC, a television signal subjected to gamma correction as shown in FIG. 6, CC is used.

When the high-efficiency code is decoded and an image is reproduced on a cathode ray tube, inverse gamma correction as shown at CB in FIG. 6 is applied.

If no distortion occurs due to image data compression,
For example, as shown in FIG. 6, data DAI and D^2 from a television camera are each quantized at a level of 4.9 and reproduced at their true value on a cathode ray tube.

However, if distortion occurs [i.e., level 4.
9 becomes level 5.10], it will be reproduced at a level different from its true value even on a cathode ray tube. As shown in FIG. 7, the magnitude of the distortion is larger in the distortion B caused by levels 9→10 than in the distortion A caused by levels 4→5. In other words, even if a certain amount of distortion occurs, there is a problem in that it is not very noticeable on the cathode ray tube in areas where the luminance value is small, but is particularly noticeable in areas where the luminance value is large.

By the way, in conventional variable length ADRC, in order to perform efficient encoding, bit allocation is performed, for example, as shown in FIG. 8, taking visual characteristics into consideration. According to this, by changing the bit allocation for encoding according to the size of the dynamic range of each block, control is performed so that the maximum distortion is equal to or less than a certain value. However, there is a problem in that no consideration is given to the magnitude of luminance values within a block, and distortion is noticeable in areas with large luminance values.

Therefore, an object of the present invention is to provide a highly efficient encoding device that can reduce distortion caused by compression of image data in areas with large luminance values.

[Means to solve the problem]

This invention divides a plurality of pixels of a digital video signal that has been subjected to gamma correction into a plurality of blocks, and also performs bit allocation in accordance with the dynamic range.
In a high-efficiency encoding device that compresses the amount of data held by a pixel, compression of digital video signals is performed by increasing the number of bits allocated to parts with large luminance values compared to the number of bits allocated to parts with small luminance values. (The structure is as follows.

[Effect]

Since the number of bits allocated to portions with large brightness values is greater than the number of bits allocated to portions with small brightness values, maximum distortion when brightness values are large can be reduced.

Also, the number of bits allocated to the part with small brightness value is
It is smaller than the number of bits allocated to areas with large brightness values. Since image quality degradation is not visually noticeable in areas with small brightness values, even if there is a little bit of distortion, it is not identified and is allocated. The number of bits is small (but there is no problem. Therefore, the amount of data can be further compressed for parts with small brightness values.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5. In this embodiment, the present invention is applied to two-dimensional ADRC.

In FIG. 1, for example, a digital video signal SDV in which l samples are quantized with 8 bits and gamma corrected is as follows.
It is supplied to the blocking circuit 2 via the terminal 1. In the digital video signal SDV, data in the television scanning order is divided into blocks, which are units of encoding, in a blocking circuit 2, and converted into data in the block order.

In the blocking circuit 2, for example, (520 lines x 720 lines
One frame of the screen of pixels (pixels) is (MXN
) is subdivided into blocks. For example, one block is (4
(line x 4 pixels). The digital video signal SOV converted into this block order is supplied block by block to a maximum value detection circuit 3, a minimum value detection circuit 4, and a delay circuit 5, respectively.

Digital video signal SD supplied to maximum value detection circuit 3
From the pixel data PD of V, the maximum value MAX for each block
is detected. The minimum value MIN for each block is detected from the pixel data PD of the digital video signal SDV supplied to the minimum value detection circuit 4. The maximum value MAX is supplied to the delay circuit 6, the subtraction circuit 7, and the ROMB, and the minimum value MIN is supplied to the subtraction circuits 7.9, respectively. The pixel data PD of the digital video signal SDV supplied to the delay circuit 5 is output with a delay equal to the delay amount of each of the maximum value detection circuit 3 and minimum value detection circuit 4, and is supplied to the subtraction circuit 9. .

From the maximum value MAX mentioned above, the minimum value MI is obtained by the subtraction circuit 7.
By subtracting N, a dynamic range OR is formed. This dynamic range OR is determined by the delay circuit 10
and is supplied to ROM8. By the maximum value MAX, R
Inside the OMB, the bit allocation table TB [any one of TB1 to TB4] shown in FIGS. 2 to 5 is selected. For example, when the maximum value MAX is (MA≧200), the bit allocation table TBI in Fig. 2 is selected, and when the maximum value MAX is (70 × MAX < 200), the bit allocation table TB2 in Fig. 3 is selected. selected, and the maximum value MAX is (
30<MAχ≦70), the bit allocation table TB3 in FIG. 4 is selected, and the maximum value MAX is (MAX≦30).
In this case, the bit allocation table TB4 shown in FIG. 5 is selected. Then, in the selected bit allocation table TB,
The number of bits corresponding to the dynamic range DR mentioned above is selected to form the quantization step Δ.

As shown in FIGS. 2 to 5, this bit allocation table TB increases the number of bits allocated to that block as the maximum value MAX within a block increases, and quantizes with a finer quantization step Δ. do.

On the other hand, the smaller the maximum value MAX in a block, the smaller the number of bits allocated to that block, and quantization is performed with a rougher quantization step Δ.

By this processing, the maximum distortion can be reduced compared to the conventional method, and the distortion can be made less noticeable on the cathode ray tube. Further, since portions with small luminance values are not visually noticeable, even if there is a little amount of distortion, it will not be discriminated, and the number of bits to be allocated can be reduced. As a result, it becomes possible to further compress the amount of data in portions where the luminance value is small. As shown in this embodiment, the bit allocation is adaptively changed based on the maximum value MAX and the dynamic range DR, which is more effective when the block size is large. Further, in the conventional high-efficiency encoding device, the additional bits for each block are the dynamic range and the minimum value, but in this embodiment as well, only the dynamic range and the maximum value are required, so the additional bits do not increase.

The quantization step Δ is supplied from the ROM 8 to the quantization circuit 11, and a bit number code Nb indicating the number of allocated bits is also supplied.
is supplied to the framing circuit 12.

The variable number of bits is encoded based on the bit allocation table TH stored in the ROMB.

In this encoding, the maximum distortion changes according to the maximum value MAX and the dynamic range OR.
It can be seen that when AX is 200 and the dynamic range is 160, the bit allocation table TBI shown in FIG. 2 is selected and the number of allocated bits is 3 bits. Therefore, the quantization step width Δ is 20, and the maximum distortion is 10.

By subtracting the minimum value MIN from the pixel data PD of the digital video signal SDV in the above-mentioned subtraction circuit 9, pixel data PDI from which the minimum value has been removed is formed, and this pixel data PDI is sent to the quantization circuit 11. Supplied. This minimum value removed pixel data PDI and quantization step Δ
A code signal DT is formed from the frame forming circuit 12.
is supplied to

The maximum value MAX is sent to the framing circuit 12 via the delay circuit 6.
The dynamic range OR is supplied to a framing circuit 12 via a delay circuit 10. The code signal DT is then supplied from the quantization circuit 11 to the framing circuit 12, and the bit number code Nb is supplied from the ROMB to the framing circuit 12. This framing circuit 12 converts the above-mentioned maximum value MAX, dynamic range DR, and code signal port T into frame-structured recording data.

In the framing circuit 12, error correction encoding processing is performed as necessary, and the output from the framing circuit 12 is taken out from a terminal 13. In addition, the above-mentioned bit number code Nb
is used in the framing circuit 12 to select the number of valid bits.

When high-efficiency encoding was actually performed using the bit assignments shown in FIGS. 2 to 5, the distortion in areas with high brightness on the cathode ray tube was uniformly reduced, although there were some differences depending on the picture.

In this embodiment, two-dimensional ADRC is explained as an example, but the invention is not limited to this, and three-dimensional ADRC
Of course, it can also be applied to.

〔Effect of the invention〕

According to the present invention, when compressing a gamma-corrected digital video signal, the number of bits allocated to portions with large luminance values is increased compared to the number of bits allocated to portions with small luminance values. This has the effect that distortion in portions with large luminance values can be reduced and distortion in portions with large luminance values can be made less noticeable on the cathode ray tube. In addition, since the number of bits is allocated to a smaller number of bits in portions with small luminance values where distortion is less visually noticeable, there is an effect that the amount of data can be further compressed.

According to the embodiment, since only the dynamic range and the maximum value are required as the additional bits for each block, there is an advantage that there is no need to increase the number of additional bits compared to the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a high-efficiency encoding device showing an embodiment of the present invention, FIGS. 2 to 5 are explanatory diagrams showing bit allocation according to the maximum value of pixel data, and FIGS. 7
The figures are characteristic diagrams showing the characteristics of a cathode ray tube and a television camera, respectively, and FIG. 8 is an explanatory diagram showing bit allocation. Explanation of main symbols in the drawings SDV: digital video signal, PDSPDI: pixel data.

Claims (1)

[Claims] A plurality of pixels of a digital video signal subjected to gamma correction are divided into a plurality of blocks, bits are allocated in accordance with the dynamic range, and the amount of data held by the pixels is compressed. In the high-efficiency encoding device, the digital video signal is compressed using a high-efficiency encoding device characterized in that the number of bits allocated to portions with large luminance values is larger than the number of bits allocated to portions with small luminance values. Encoding device.