Fixed quality source coder with fixed threshold

• US 5,541,594 A
• Filed: 07/13/1994
• Issued: 07/30/1996
• Est. Priority Date: 03/28/1994
• Status: Expired due to Term

• Current Assignee: Utah Valley University
• Original Assignee: Utah Valley University
• Inventors: Harris, Richard W., Huang, Chien-Min, Israelsen, Paul D.
• Primary Examiner(s): Williams, Howard L.
• Application Number:
  US08/274,622
• Time in Patent Office: 748 Days
• Field of Search: 341/51, 341/67, 341/76, 341/106, 348/414, 348/417, 348/418, 348/422
• US Class Current: 341/51
• CPC Class Codes: G06T 9/008 Vector quantisation
• CPC Class Codes: H03M 7/3082 Vector coding for television signals, see H04N19/94
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/162 User input
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/94 Vector quantisation

Abstract

A fixed quality source coder receives and performs VQ on an input signal I_D. The signal I_D may be characterized by the number of samples/frame and bits per sample, and may be provided by a traditional source coder. The traditional source coder may include a sample-and-hold (S/H) circuit producing rxs samples/frame and an ADC providing n bits per pixel. In a first embodiment, the number of bits/sample is increased. In the second embodiment, the number of samples/frame is increased. In a third embodiment, both the number of bits/sample and the number of samples/frame are increased. Measurements made in simulations involving the first and second embodiments show that the fixed quality source coder has a smaller data rate, mean absolute error (MAE) and root mean square error (RMSE) than that of the traditional source coder, while maintaining the same or less maximum error. The fixed quality source coder includes an encoder and may also include a decoder. The encoder may include a lossy codec that receives and encodes the signal I_D to provide encoded information to a multiplexer regarding the signal I_D. The lossy codec also decodes the encoded signal to produce a decoded signal I_VQ^-1. A summer receives I_D and I_VQ^-1 and determines an error signal E_R, where E_R may equal I_D -I_VQ^-1. A threshold circuit receives the signal E_R and passes a threshold signal E_T, where a threshold level T may be set to ensure that the maximum error allowed in the encoder is equal to a particular desired maximum error.

Claims

1. A fixed quality source coder for encoding a digital signal I_D which comprises a first series of separate data respectively representing multiple pixels, the coder comprising:

codec means receiving the signal I_D for encoding the signal I_D to provide encoded information regarding the signal I_D and for decoding the encoded signal to produce a decoded signal I_VQ^-1 which comprises a second series of separate data respectively representing the multiple pixels;

means for determining an error signal E_R which comprises a third series of separate data that is the result of a comparison of the first series of separate data and the second series of separate data for each of the multiple pixels;

threshold means receiving the signal E_R for passing a truncated error signal E_T for each of the multiple pixels based on a comparison of E_R and fixed threshold value T; and

lossless encoder means for receiving and encoding the signal E_T to provide a signal E_T.

2. The coder of claim 1 in which the threshold value T is selected by a user.

3. The coder of claim 1, further comprising:

multiplexing means that receives the signal E_T and the encoded information regarding the signal I_D for multiplexing the signal E_T and the encoded information regarding the signal I_D to provide a multiplexed signal responsive to the signal E_T and the encoded information regarding the signal I_D ;

demultiplexing means that receives the multiplexed signal for providing a demultiplexed signal responsive thereto; and

decoding means that receives the demultiplexed signal for providing a decoded signal I_RD responsive thereto, which is a reconstruction of the signal I_D, wherein a difference between the signal I_D and the decoded signal I_RD less than the threshold T.

4. The coder of claim 1 in which the signal I_D has n+k bits and the fixed quality source coder has a maximum error that is no greater than that of the n-bit analog to digital converter, but with an average error and a data rate that are substantially smaller than that of the n-bit analog to digital converter.

5. The coder of claim 1 in which the signal I_D has RxS samples/frame and the fixed quality source coder has a maximum error that is no greater than that of a signal having rxs samples/frame where R is larger than r and S is larger than s, but with an average error and a data rate that are substantially smaller than that of the signal having rxs samples/frame.

6. The coder of claim 1 in which the signal I_D has n+k bits and threshold T is equal to the least significant bit of an n-bit analog-to-digital converter.

7. The coder of claim 1 in which the codec means includes a lossy encoder that performs multi-stage tree adaptive search vector quantization.

8. The coder of claim 1 in which E_R =I_D -I_VQ^-1.

9. The coder of claim 1 in which E_T =E_R -T when E_R >

T, E_T =0 when -T≦

E_R ≦

T, and E_T =E_R +T when E_R <

-T.

10. The coder of claim 1 in which E_T =E_R -T when E_R ≧

T, E_T =0 when -T≦

E_R <

T, and E_T =E_R +T when E_R <

-T.

11. The coder of claim 1 in which E_T =E_R -T when E_R >

T, E_T =0 when -T<

E_R ≦

T, and E_T =E_R +T when E_R ≦

-T.

12. The coder of claim 1 in which E_T =E_R -T when E_R ≧

T, E_T =0 when -T<

E_R <

T, and E_T =E_R +T when E_R ≦

-T.

13. A fixed quality source coder for encoding a digital signal I_D, the coder comprising:

a codec that receives and encodes the signal I_D to provide encoded information regarding the signal I_D and decodes the encoded signal to produce a decoded signal I_VQ^-1 ;

means for determining an error signal E_R by comparing the signal I_D and decoded signal I_VQ^-1 ;

a threshold circuit that receives the signal E_R and passes a truncated error signal E_T based on a fixed threshold value T; and

a lossless encoder that receives and encodes the signal E_T to provide a signal E_T.

14. The coder of claim 13 in which the threshold value T is selected by a user.

15. The coder of claim 13, further comprising:

a multiplexer that receives the signal E_T and the encoded information regarding the signal I_D for multiplexing the signal E_T and the encoded information regarding the signal I_D to provide a multiplexed signal responsive to the signal E_T and the encoded information regarding the signal I_D ;

a demultiplexer that receives the multiplexer signal and provides a demultiplexed signal responsive thereto; and

a decoder that receives the demultiplexed signal and provides a decoded signal I_RD responsive thereto, which is a reconstruction of the signal I_D.

16. The coder of claim 13 in which the signal I_D has n+k bits and the fixed quality source coder has a maximum error that is no greater than that of the n-bit analog to digital converter, but with an average error and a data rate that are substantially smaller than that of the n-bit analog to digital converter.

17. The coder of claim 13 in which the signal I_D has RxS samples/frame and the fixed quality source coder has a maximum error that is no greater than that of a signal having rxs samples/frame where R is larger than r and S is larger than s, but with an average error and a data rate that are substantially smaller than that of the signal having rxs samples/frame.

18. The coder of claim 13 in which the codec is a lossy codec and includes a lossy encoder.

19. The coder of claim 13 in which E_R =I_D -I_VQ^-1.

20. The coder of claim 13 in which E_T =E_R -T when E_R >

T, E_T =0 when -T≦

E_R ≦

T, and E_T =E_R +T when E_R <

-T.