Method and apparatus for digital image decoding

• US 6,208,689 B1
• Filed: 02/26/1997
• Issued: 03/27/2001
• Est. Priority Date: 03/04/1996
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Asai, Kohtaro, Murakami, Tokumichi, Asano, Kenichi, Ohira, Hideo, Shimada, Toshiaki
• Primary Examiner(s): Kelley, Chris S.
• Assistant Examiner(s): PHILIPPE, GIMS S
• Application Number:
  US08/806,668
• Time in Patent Office: 1,490 Days
• Field of Search: 348/405, 348/415, 348/420, 348/410, 348/419, 348/404, 348/406, 348/407, 348/408, 348/421, 348/27, 395/114, 395/115, 382/251, 375/240.12, 375/240.03, 375/240.24
• US Class Current: 375/240.12
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/177 the unit being a group of pictures [GOP]
• CPC Class Codes: H04N 19/423 characterised by memory arrangements H04N19/433 takes precedence
• CPC Class Codes: H04N 19/428 Recompression, e.g. by spatial or temporal decimation
• CPC Class Codes: H04N 19/577 Motion compensation with bidirectional frame interpolation, i.e. using B-pictures
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A method and apparatus of digital image decoding is provided for reducing compression-related deterioration of an image to a minimum with a reduced storage capacity. The digital image decoding apparatus is equipped with a compression rate judging section for judging an optimal rate of compression for effecting the least deterioration to the image based upon the size of image in connection with the storage capacity of a frame memory. A compressing section compresses decoded data based upon the optimal rate of compression and sends the compressed data to a predictive/display frame memory for storage. An expanding A section expands the compressed data based upon the optimal rate of compression and sends the expanded data to a decoding section when the expanded data is required. An expanding B section reads out the compressed data of a display frame from the predictive/display frame memory and expands the compressed data based upon the optimal rate of compression and sends the expanded data to a display unit for display.

Claims

1. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing data on a frame basis;

a decoding section for inputting the encoded data which is encoded in accordance with an inter/intra-frame coding in a digital image coding apparatus and decoding the encoded data in accordance with an inter/intra-frame decoding on the frame basis and outputting decoded data;

a compressing section, locating between the frame memory and the decoding section, for inputting the decoded data outputted from the decoding section, compressing the decoded data in accordance with a non-inter/intra-frame coding and outputting compressed data to the frame memory so as to store the compressed data to the frame memory; and

an expanding section, locating between the frame memory and the decoding section, for reading out and expanding the compressed data stored in the frame memory and in accordance with a non-inter/intra-frame decoding and outputting expanded data to the decoding section,

wherein said frame memory includes a predictive frame memory for storing the encoded data of a predictive frame to be used for predictive decoding the encoded data in said decoding section, and a display frame memory for storing the encoded data of a display frame to be used for display;

wherein said compressing section compresses the decoded data of the predictive frame to be stored in said predictive frame memory as compressed predictive data, and the decoded data of the display frame to be stored in said display frame memory as compressed display data; and

wherein said expanding section includes

a predictive data expanding section for expanding the compressed data of the predictive frame stored in said predictive frame memory and outputting expanded predictive data, and

a display data expanding section for expanding the compressed data of the display frame stored in said display frame memory and outputting the expanded display data for display.

2. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing data on a frame basis;

a decoding section for inputting the encoded data which is encoded in accordance with an inter/intra-frame coding in a digital image coding apparatus and decoding the encoded data in accordance with an inter/intra-frame decoding on the frame basis and outputting decoded data;

a compressing section, locating between the frame memory and the decoding section, for inputting the decoded data outputted from the decoding section, compressing the decoded data in accordance with a non-inter/intra-frame coding and outputting compressed data to the frame memory so as to store the compressed data to the frame memory; and

an expanding section, locating between the frame memory and the decoding section, for reading out and expanding the compressed data stored in the frame memory and in accordance with a non-inter/intra-frame decoding and outputting expanded data to the decoding section,

wherein said decoding section decodes the encoded data sequentially on a block basis and outputs block-based decoded data; and

wherein said compressing section compresses the block-based decoded data in a period shorter than a period for decoding the block-based encoded data in said decoding section.

3. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing data on a frame basis;

a decoding section for inputting the encoded data which is encoded in accordance with an inter/intra-frame coding in a digital image coding apparatus and decoding the encoded data in accordance with an inter/intra-frame decoding on the frame basis and outputting decoded data;

a compressing section, locating between the frame memory and the decoding section, for inputting the decoded data outputted from the decoding section, compressing the decoded data in accordance with a non-inter/intra-frame coding and outputting compressed data to the frame memory so as to store the compressed data to the frame memory;

an expanding section, locating between the frame memory and the decoding section, for reading out and expanding the compressed data stored in the frame memory and in accordance with a non-inter/intra-frame decoding and outputting expanded data to the decoding section,

wherein said decoding section decodes the encoded data including profile information of a coding method for the encoded data; and

a profile judging section for receiving the encoded data and judging the profile of the coding method;

wherein said compressing section, including a plurality of modes of compression, receives the profile information and selects one of the plurality of modes optimal to the coding method.

4. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing the encoded data on a frame basis;

a decoding section for decoding the encoded data on the frame basis and outputting decoded data;

a compressing section for compressing the decoded data and outputting compressed data; and

an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data;

wherein said decoding section decodes the encoded data on a block basis and outputs a block of M pixels×

N pixels×

r bits of the decoded data;

wherein said compressing section compresses the block-based decoded data to the block-based compressed data through a conversion method, which calculates a coefficient of image quality of the block-based decoded data, and allocates a longer bit-length to the block-based decoded data for a coefficient highly influential on image quality, and a shorter bit-length to the decoded data for a less influential coefficient; and

wherein said compressing section converts the block-based decoded data into a fixed bit-length of the block-based compressed data.

5. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing the encoded data on a frame basis;

a decoding section for decoding the encoded data on the frame basis and outputting decoded data;

a compressing section for compressing the decoded data and outputting compressed data; and

an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data;

wherein said frame memory includes a predictive frame memory for storing the encoded data of a predictive frame to be used for predictive decoding the encoded data in said decoding section, and a display frame memory for storing the encoded data of a display frame to be used for display;

wherein said compressing section compresses the decoded data of the predictive frame to be stored in said predictive frame memory as compressed predictive data, and the decoded data of the display frame to be stored in said display frame memory as compressed display data;

wherein said expanding section includes,

a predictive data expanding section for expanding the compressed data of the predictive frame stored in said predictive frame memory and outputting expanded predictive data, and

a display data expanding section for expanding the compressed data of the display frame stored in said display frame memory and outputting the expanded display data for display;

wherein said compressing section compresses the frame-based decoded predictive data on a block basis and outputs the compressed data on the block basis;

wherein said predictive data expanding section reads out a block of the compressed predictive data on the block basis including at least a part of a block data of K pixels×

L lines required by said decoding section, the required block data being a part of a predictive frame stored in said predictive frame memory, expands the read out block of the block-based compressed predictive data, and outputs the block-based expanded predictive data of the read out block including the required block data of K pixels×

L lines to said decoding section;

wherein said predictive data expanding section includes a block memory for storing the block-based expanded predictive data of the read out block from said predictive frame memory, and

wherein said block memory is updated on a block basis each time block data required by said decoding section is renewed.

6. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing the encoded data on a frame basis;

a decoding section for decoding the encoded data on the frame basis and outputting decoded data;

a compressing section for compressing the decoded data and outputting compressed data; and

an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data;

wherein said frame memory includes a predictive frame memory for storing the encoded data of a predictive frame to be used for predictive decoding the encoded data in said decoding section, and a display frame memory for storing the encoded data of a display frame to be used for display;

wherein said compressing section compresses the decoded data of the predictive frame to be stored in said predictive frame memory as compressed predictive data, and the decoded data of the display frame to be stored in said display frame memory as compressed display data;

wherein said expanding section includes,

a predictive data expanding section for expanding the compressed data of the predictive frame stored in said predictive frame memory and outputting expanded predictive data, and

a display data expanding section for expanding the compressed data of the display frame stored in said display frame memory and outputting the expanded display data for display;

wherein said compressing section compresses the frame-based decoded display data on a block basis and outputs the compressed display data on the block basis;

wherein said display data expanding section reads out the compressed display data stored in said display frame memory on the block basis, expands the read out block-based compressed display data, and outputs the block-based expanded display data sequentially in a horizontal scanning direction;

wherein said display data expanding section includes,

a block memory for storing the read out block of the block-based expanded display data sequentially with a width and direction in accordance with the horizontal scanning direction; and

wherein said display data expanding section outputs the block-based expanded display data read out from said display memory in response to an image display scan line.

7. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing data on a frame basis;

a decoding section for inputting the encoded data which is encoded in accordance with an inter/intra-frame coding in a digital image coding apparatus and decoding the encoded data in accordance with an inter/intra-frame decoding on the frame basis and outputting decoded data;

a compressing section, locating between the frame memory and the decoding section, for inputting the decoded data outputted from the decoding section, compressing the decoded data in accordance with a non-inter/intra-frame coding and outputting compressed data to the frame memory so as to store the compressed data to the frame memory;

an expanding section, locating between the frame memory and the decoding section, for reading out and expanding the compressed data stored in the frame memory and in accordance with a non-inter/intra-frame decoding and outputting expanded data to the decoding section,

wherein said compressing section includes

a plurality of quantizers, each of which has a table for a unique quantization and outputs a unique quantized result of the decoded data, an optimal table selector for comparing the unique quantized results for selecting a table optimal to the decoded data from among the plurality of tables, and

a selector for selecting an output from one of the plurality of quantizers having the optimal table selected by said optimal table selector.

8. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing the encoded data on a frame basis;

a decoding section for decoding the encoded data on the frame basis and outputting decoded data;

a compressing section for compressing the decoded data and outputting compressed data; and

an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data;

a compression rate judging section for receiving image size information for indicating the given size of the image and judging a rate of compression for the compressed data to be stored in said frame memory based upon the given size of the image and a capacity of said frame memory;

wherein said compressing section compresses the decoded data based upon the rate of compression and outputs the compressed data to said frame memory; and

wherein said expanding section reads out the compressed data from said frame memory and expands the compressed data based upon the rate of compression.

9. The digital image decoding apparatus of claim 8,

wherein the encoded data includes image size information; and

wherein said compression rate judging section receives the encoded data and extracts the image size information from the encoded data.

10. The digital image decoding apparatus of claim 8,

wherein said compressing section is provided with a plurality of modes of compression;

and

wherein said compressing section selects one mode from among the plurality of modes, the selected mode producing an amount of compressed data less than the capacity of said frame memory.

11. The digital image decoding apparatus of claim 10,

wherein said compressing section compresses the decoded data on a block basis of M pixels×

N pixels×

r bits through a quantization based upon a One Detention Differential Pulse Code Modulation (1D-DPCM) method;

wherein said compressing section quantizes a heading pixel of a given L number of pixels (L≦

M) with a quantum of t bits (t≦

r), and a difference between adjacent two pixels of remaining pixels of the given L pixels with a quantum of p bits (p≦

r); and

wherein said compressing section modifies at least one of values of L, p, and t adaptively for providing a plurality of the modes of compression.

12. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing the encoded data on a frame basis;

a decoding section for decoding the encoded data on the frame basis and outputting decoded data;

a compressing section for compressing the decoded data and outputting compressed data; and

an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data;

wherein said decoding section decodes the encoded data including profile information of a coding method for the encoded data;

said digital image decoding apparatus further comprising;

a profile judging section for receiving the encoded data and judging the profile of the coding method; and

wherein said compressing section, including a plurality of modes of compression, receives the profile information and selects one of the plurality of modes optimal to the coding method;

wherein said profile judging section judges the coding method at least one of a bidirectional prediction inter-frame coding method for predicting a frame based upon past and future frames and of a forward prediction inter-frame coding method based upon a past frame; and

wherein said compressing section compresses the decoded data including bidirectional prediction inter-frame encoding method and does not compress the decoded data including the forward prediction inter-frame encoding method.

13. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing data on a frame basis;

a decoding section for inputting the encoded data which is encoded in accordance with an inter/intra-frame coding in a digital image coding apparatus and decoding the encoded data in accordance with an inter/intra-frame decoding on the frame basis and outputting decoded data;

a compressing section, locating between the frame memory and the decoding section, for inputting the decoded data outputted from the decoding section, compressing the decoded data in accordance with a non-inter/intra-frame coding and outputting compressed data to the frame memory so as to store the compressed data to the frame memory;

an expanding section, locating between the frame memory and the decoding section, for reading out and expanding the compressed data stored in the frame memory and in accordance with a non-inter/intra-frame decoding and outputting expanded data to the decoding section,

wherein said compressing section includes a quantizing section for quantizing the decoded data on a block basis of M×

N pixels to output the block-based compressed data; and

wherein said expanding section includes an expander for dequantizing the block-based compressed data and outputting the expanded data on the block basis of M×

N pixels.

14. A digital image decoding apparatus for decoding encoded data of an image with a given size, said digital image decoding apparatus comprising:

a frame memory having a capacity for storing the encoded data on a frame basis;

a decoding section for decoding the encoded data on the frame basis and outputting decoded data;

a compressing section for compressing the decoded data and outputting compressed data; and

an expanding section for reading out and expanding the compressed data stored in the frame memory and outputting expanded data;

wherein said compressing section includes a quantizing section for quantizing the decoded data on a block basis of M×

N pixels to output the block-based compressed data;

wherein said expanding section includes an expander for dequantizing the block-based compressed data and outputting the expanded data on the block basis of M×

N pixels;

wherein said quantizing section includes a plurality of quantizers, each of which has a unique characteristic of quantization,

wherein said compressing section includes,

a characteristic searching section for searching a characteristic of the block-based decoded data of M×

N pixels, and

a quantizer selector for selecting one of the plurality of quantizers in said quantizing section based upon the characteristic searched by said characteristic searching section, and activating a selected quantizer exclusively for quantizing the block-based decoded data of M×

N pixels,

wherein said quantizer selector includes,

a maximum value detector for receiving the block-based decoded data of M×

N pixels, and calculating a maximum value of a difference between adjacent pixels and outputting a maximum value as a first characteristic,

a minimum value detector for receiving the block-based decoded data of M×

N pixels, and calculating a minimum value of the difference between adjacent pixels and outputting a minimum value as a second characteristic,

a characteristic quantization table for quantizing the first characteristic of the maximum value and the second characteristic of the minimum value, respectively,

a characteristic quantizer for receiving and quantizing the maximum and minimum values with reference to the characteristic quantization table, and outputting maximum and minimum quantized values, respectively,

a select table for selecting one of the plurality of quantizers in said quantizing section based upon the maximum and minimum quantized values, and

a selector for selecting one of the plurality of quantizers optimal to the decoded data based upon said select table.

15. The digital image decoding apparatus of claim 14, wherein said expanding section includes a plurality of dequantizers, each of which has a unique characteristic of dequantization corresponding to a respective unique characteristic of quantization of said plurality of quantizers in said quantizing section.

16. The digital image decoding apparatus of claim 15, further comprising:

a controlling section for controlling the unique characteristics of quantization of the plurality of quantizers in said compressing section and the unique characteristics of dequantization of the plurality of dequantizers in said expanding section.

17. The digital image decoding apparatus of claim 16,

wherein respective quantizers in the quantizing section modifies the characteristic of quantization adaptively;

wherein the respective dequantizers in said expanding section modify the characteristic of dequantization correspondingly to the modification of the characteristic of quantization;

wherein said controlling section includes,

a quantization/dequantization characteristic setting section for setting the respective quantizers to modify the unique characteristic of quantization and setting the respective dequantizers to modify the unique characteristic of dequantization,

a select table setting section for setting the quantizer selector to refer to the select table in accordance with the setting of the unique characteristics of quantization/dequantization, and

a characteristic quantization table setting section for setting said characteristic quantizer to refer to the characteristic quantization table in accordance with the setting of the unique characteristics of quantization/dequantization.

18. A method for digital image decoding, the method comprising the steps of:

inputting encoded data through an inter-/intra-frame coding on a block basis of M×

N pixels;

after the inputting step, decoding the encoded data through an inter/intra-frame decoding on a block basis of M×

N pixels;

after the decoding step, compressing the block-based decoded data of M×

N pixels through quantization, not through an inter/intra-frame coding, and outputting block-based compressed data;

after the compressing step, storing a predictive frame of the block-based compressed data on a frame basis in a predictive frame memory of a frame memory, the predictive frame being used to decode the encoded data through inter-/intra- frame coding;

after the compressing step, storing a display frame of the block-based compressed data in a display frame memory of the frame memory, the display frame being used to display an image;

after the predictive frame storing step, expanding the compressed predictive frame data read out from the predictive frame memory through a dequantization, not through an inter/intra-frame decoding, of the compressed predictive frame data, and supplying an expanded predictive frame data to said decoding step;

after the display frame storing step, expanding the compressed display data read out from the display frame memory, through a dequantization, not through an inter/intra-frame decoding, of the compressed display frame data, and outputting an expanded display frame data as image display data; and

judging a rate of compression of the block-based decoded data based upon a size of image judged by the encoded data in connection with a storage capacity of the frame memory and providing said compressing step with the rate of compression as compression rate information.

19. The method of claim 18, further comprising the step of:

controlling a setting and modifying of a quantization characteristic for quantization in said compressing step and a setting and modifying of a dequantization characteristic for the dequantization in said expanding steps.