Transcoding apparatus and method

• US 6,650,707 B2
• Filed: 03/02/2001
• Issued: 11/18/2003
• Est. Priority Date: 03/02/2001
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Youn, Jeongnam, Wang, Wen-Hao, Sun, Ming-Ting, Lin, Chia-Wen
• Primary Examiner(s): Diep, Nhon
• Application Number:
  US09/796,600
• Publication Number:
  US 20020163967A1
• Time in Patent Office: 991 Days
• Field of Search: H04/N.712, 375/240.12, 375/240.25, 375/240.18, 348/401.1, 348/403.1, 348/394.1
• US Class Current: 375/240.12
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

A transcoder for transcoding digital video signals includes a decoder and an encoder. In the decoder, an end-of-block (EOB) position of an incoming block received by the decoder is determined and a discrete cosine transform (DCT) block type is determined based on the determined EOB position. A reduced number of DCT coefficients is computed in a subsequent inverse DCT computation based on the DCT block type. In the encoder, if the incoming block is intercoded, no DCT coefficients are computed after the EOB of the incoming blocks is performing a DCT. Further, in the encoder when the incoming block is intercoded, an algorithm is applied to predict which DCT coefficients may become zero after a subsequent quantization operation, and only DCT coefficients that may not become zero are computed in performing the DCT.

Claims

1. A method for transcoding coded digital video signals representing blocks of pixels, comprising the steps of:

decoding inputted encoded digital signals, including the steps of

determining an end-of-block (EOB) position in an incoming block of the encoded inputted signal,

inverse quantizing the inputted signals,

determining a discrete cosine transform (DCT) block type based on the EOB position, and

performing partial inverse DCT computations based on the DCT block type to provide decoded signals; and

encoding the decoded signals, including the steps of

determining if an incoming block of the decoded signals is intracoded or intercoded,

performing a DCT of the decoded signals by selecting, if the incoming block is intracoded, DCT coefficients from the inverse quantized inputted signals to provide transformed signals, and

performing a DCT of the decoded signal by computing, if the incoming block is intercoded, selected DCT coefficients located before the EOB position of the incoming block to provide transformed signals.

2. The method of claim 1 wherein the step of computing selected DCT coefficients includes steps of:

predicting which DCT coefficients may become zero after a subsequent quantization step; and

only computing DCT coefficients that may not become zero after the subsequent quantization step.

3. The method of claim 1 further including a step of motion compensating the decoded signals.

4. The method of claim 1 further including steps of:

quantizing the transformed signals to provide encoded signals; and

performing motion compensation on the encoded signals.

5. The method of claim 1 wherein the step of determining a DCT block type includes steps of:

determining a first DCT block type if the EOB position=0, for which all DCT coefficients are zero;

determining a second DCT block type if the EOB position=1, for which the incoming block of the encoded signal has only a DC component;

determining a third DCT block type if 1<

the EOB position<

4, for which at most three low frequency DCT coefficients need be computed;

determining a fourth DCT block type if 3<

the EOB position<

11, for which at most ten low frequency DCT coefficients need be computed; and

determining a fifth DCT block type if the EOB position>

10, for which all non-zero DCT coefficients need be computed.

6. The method of claim 1 wherein the step of performing a DCT, if the incoming block is intercoded, includes a substep of only computing the selected DCT coefficients located before the EOB position.

7. A method for transcoding coded digital video signals representing blocks of pixels, comprising the steps of:

decoding inputted encoded digital signals, including steps of

determining an end-of-block (EOB) position in an incoming block of the encoded inputted signal,

inverse quantizing the inputted signals,

determining a discrete cosine transform (DCT) block type based on the EOB position, and

performing partial inverse DCT computations based on the DCT block type to provide decoded signals; and

encoding the decoded signals.

8. The method of claim 7 wherein the step of determining a DCT block type includes steps of:

determining a first DCT block type if the EOB position=0, for which all DCT coefficients are zero;

determining a second DCT block type if the EOB position=1, for which the incoming block of the encoded signal has only a DC component;

determining a third DCT block type if 1<

the EOB position<

4, for which at most three low frequency DCT coefficients need be computed;

determining a fourth DCT block type if 3<

the EOB position<

11, for which at most ten low frequency DCT coefficients need be computed; and

determining a fifth DCT block type if the EOB position>

10, for which all non-zero DCT coefficients need be computed.

9. A method for transcoding coded digital video signals representing blocks of pixels, comprising the steps of:

decoding inputted encoded digital signals, including steps of

determining an end-of-block (EOB) position in an incoming block of the encoded inputted signal prior to inverse quantizing,

inverse quantizing the inputted signals, and

encoding the decoded signals, including steps of

determining if an incoming block of the decoded signals is intracoded or intercoded,

performing a discrete cosine transform (DCT) of the decoded signals by selecting, if the incoming block is intracoded, DCT coefficients from the inverse quantized inputted signals to provide transformed signals, and

performing a DCT of the decoded signal by computing, if the incoming block is intercoded, selected DCT coefficients located before the EOB position of the incoming block to provide transformed signals.

10. The method of claim 9 wherein the step of computing selected DCT coefficients includes steps of:

predicting which DCT coefficients may become zero after a subsequent quantization step; and

only computing DCT coefficients that may not become zero after the subsequent quantization step.

11. A transcoder for transcoding coded digital video signals representing blocks of pixels, comprising:

a decoder for decoding inputted coded digital signals, including

means for determining an end-of-block (EOB) position in an incoming block of the encoded inputted signal,

an inverse quantizer for inverse quantizing the inputted signals,

means for determining a discrete cosine transform (DCT) block type based on the EOB position, and

an inverse discrete cosine transformer for performing partial inverse DCT computations based on the determined DCT block type to provide decoded signals; and

an encoder to encode the decoded signals.

12. The transcoder of claim 11, wherein the means for determining a DCT block type includes:

means for determining a first DCT block type if the EOB position=0, for which all DCT coefficients are zero;

means for determining a second DCT block type if the EOB position=1, for which the incoming block of the encoded signal has only a DC component;

means for determining a third DCT block type if 1<

the EOB position<

4, for which at most three low frequency DCT coefficients need be computed;

means for determining a fourth DCT block type if 3<

the EOB position<

11, for which at most ten low frequency DCT coefficients need be computed; and

means for determining a fifth DCT block type if the EOB position>

10, for which all non-zero DCT coefficients need be computed.

13. A transcoder for transcoding digital video signals representing blocks of pixels, comprising:

a decoder for decoding inputted encoded digital signals, including

means for determining an end-of-block (EOB) position in an incoming block of the encoded inputted signals; and

an inverse quantizer for inverse quantizing the inputted signal, and

an encoder to encode the decoded signals, the encoder including

means for determining if an incoming block of the decoded signals is intracoded or intercoded, and

a discrete cosine transformer for performing a discrete cosine transform (DCT) of the decoded signals by selecting, if the incoming block is intracoded, DCT coefficients determined from the inverse quantized inputted signals, the discrete cosine transformer performing the DCT by computing, if the incoming block is intercoded, selected DCT coefficients located before the EOB position of the incoming block.

14. The transcoder of claim 13, further including a quantizer for quantizing transformed signals provided by the discrete cosine transformer;

the discrete cosine transformer further including

means for predicting which DCT coefficients may become zero after quantization by the quantizer, and

means for only computing DCT coefficients that may not become zero after the quantization.