Picture transmission system using minimal reference-frame modification to recover from transmission errors
First Claim
1. A method of recovering from a transmission error in a picture transmission system that transmits a series of pictures from a coding apparatus to a decoding apparatus, each picture in the series being coded at the coding apparatus with reference to a preceding picture in the series, and decoded at the decoding apparatus with reference to the same preceding picture in the series, comprising the steps of:
- (a) detecting a decoding error, caused by said transmission error, at said decoding apparatus;
(b) transmitting an error signal from said decoding apparatus to said coding apparatus, informing said coding apparatus of said coding error;
(c) selecting a reference picture in said series of pictures;
(d) determining a part of said reference picture made undecodable by said decoding error;
(e) modifying said part of said reference picture in said coding apparatus, thereby obtaining a first modified reference picture;
(f) identically modifying said part of said reference picture in said decoding apparatus, thereby obtaining a second modified reference picture;
(g) coding a subsequent picture, following said reference picture in said series, with reference to said first modified reference picture at said coding apparatus; and
(h) decoding said subsequent picture with reference to said second modified reference picture at said decoding apparatus.
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Abstract
In a picture transmission system that transmits a series of pictures from a coding apparatus to a decoding apparatus, each picture being coded and decoded with reference to a preceding picture, when a transmission error occurs, the decoding apparatus detects a decoding error caused by the transmission error and sends an error signal to the coding apparatus. The coding apparatus and decoding apparatus then both modify part of a reference picture affected by the decoding error, making identical modifications. A subsequent picture is coded and decoded with reference to the modified reference picture, thereby recovering from the transmission error with minimum loss of coding efficiency and picture quality.
81 Citations
57 Claims
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1. A method of recovering from a transmission error in a picture transmission system that transmits a series of pictures from a coding apparatus to a decoding apparatus, each picture in the series being coded at the coding apparatus with reference to a preceding picture in the series, and decoded at the decoding apparatus with reference to the same preceding picture in the series, comprising the steps of:
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(a) detecting a decoding error, caused by said transmission error, at said decoding apparatus;
(b) transmitting an error signal from said decoding apparatus to said coding apparatus, informing said coding apparatus of said coding error;
(c) selecting a reference picture in said series of pictures;
(d) determining a part of said reference picture made undecodable by said decoding error;
(e) modifying said part of said reference picture in said coding apparatus, thereby obtaining a first modified reference picture;
(f) identically modifying said part of said reference picture in said decoding apparatus, thereby obtaining a second modified reference picture;
(g) coding a subsequent picture, following said reference picture in said series, with reference to said first modified reference picture at said coding apparatus; and
(h) decoding said subsequent picture with reference to said second modified reference picture at said decoding apparatus. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
(i) sending information from said coding apparatus to said decoding apparatus, notifying said decoding apparatus that said coding apparatus has modified said reference picture.
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4. The method of claim 3, wherein said step (i) is performed repeatedly.
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5. The method of claim 1 wherein, in said steps (e) and (f), said part of said reference picture is modified by use of another part of said reference picture.
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6. The method of claim 1 wherein, in said steps (e) and (f), said part of said reference picture is modified by use of a corresponding part of a picture preceding said reference picture in said series.
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7. The method of claim 1, wherein said step (f) further comprises the steps of:
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(j) modifying a first picture, in which said decoding error occurred, by using data unaffected by said decoding error to replace data affected by said coding error; and
(k) modifying each picture in said series affected by propagation of said decoding error, by using data unaffected by said decoding error to replace data affected by propagation of said coding error, until said reference picture has been modified.
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8. The method of claim 1, wherein said coding apparatus and said decoding apparatus perform motion compensation, using motion vectors, and said step (d) comprises using said motion vectors to determine error propagation.
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9. The method of claim 1, wherein said step (d) determines, as said part of said reference picture, all parts of said reference picture affected by said coding error.
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10. The method of claim 1, wherein said step (d) determines, as said part of said reference picture, those parts of said reference picture affected to at least a predetermined degree by said coding error.
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11. The method of claim 1, wherein said steps (e) and (f) are carried out according to a predetermined modification procedure.
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12. The method of claim 1, further comprising the steps of:
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(l) selecting a modification procedure for use in said step (f) at said decoding apparatus; and
(m) transmitting information describing said modification procedure from said decoding apparatus to said coding apparatus, for use in said step (e);
said steps (l) and (m) being performed by said decoding apparatus.
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13. A picture transmission system comprising:
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a coding apparatus receiving a series of pictures, coding each picture in said series with reference to a preceding picture in said series, transmitting resulting coded data on a communication link, receiving from said communication link an error signal specifying a part of one of said pictures in which a decoding error occurred, selecting a picture in said series affected by said decoding error as a reference picture, modifying a part of said reference picture affected by said decoding error to obtain a first modified reference picture, and coding a subsequent picture in said series, following said reference picture, with reference to said first modified reference picture; and
a decoding apparatus receiving said coded data from said communication link, decoding said coded data to reproduce said series of pictures, temporarily storing each decoded picture in said series for reference in decoding a further picture in said series, detecting said decoding error, transmitting said error signal over said communication link to said coding apparatus, selecting the reference picture also selected by said coding apparatus, modifying said part of said reference picture after decoding said reference picture, as said reference picture was modified by said coding apparatus, thereby obtaining a second modified reference picture, and decoding said subsequent picture with reference to said second modified reference picture. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57)
a coding unit for coding said pictures;
a reference-picture memory coupled to said coding unit, storing a plurality of pictures already coded by said coding unit;
an error-signal receiving unit receiving said error signal; and
a reference-picture modification unit coupled to said reference-picture memory and said error-signal receiving unit, modifying said reference picture in said reference-picture memory.
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33. The coding apparatus of claim 32, wherein said reference-picture modification unit determines said part of said reference picture by taking error propagation into consideration.
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34. The coding apparatus of claim 32, wherein said reference-picture modification unit modifies said part of said one of said pictures in which said decoding error occurred, then modifies pictures stored subsequently in said reference-picture memory in sequence from said one of said pictures to said reference pictures, in each case modifying those parts that were coded with reference to any already modified part of an already modified picture from said one of said pictures to said reference pictures.
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35. The coding apparatus of claim 32, wherein said reference-picture modification unit modifies said reference picture by replacing data affected by said decoding error with data from said reference picture not affected by said decoding error.
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36. The coding apparatus of claim 32, wherein said reference-picture modification unit modifies said reference picture by replacing data affected by said decoding error with data taken from a previous one of the pictures stored in said reference-picture memory.
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37. The coding apparatus of claim 32, wherein said reference-picture modification unit receives instructions from said decoding apparatus specifying a procedure by which said reference picture is to be modified.
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38. The coding apparatus of claim 32, further comprising an end-information generator notifying said decoding apparatus when said reference-picture modification unit has finished modifying said reference picture.
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39. The coding apparatus of claim 38, wherein said end-information generator notifies said decoding apparatus separately in reply to each error signal received from said decoding apparatus.
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40. The coding apparatus of claim 38, wherein said end-information generator notifies said decoding apparatus collectively of completion of modifications of said reference picture made in response to reception of a plurality of error signals specifying decoding errors.
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41. The coding apparatus of claim 38, wherein said end-information generator 109) notifies said decoding apparatus repeatedly that said reference-picture modification unit has finished modifying said reference picture.
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42. The coding apparatus of claim 32, wherein said reference-picture modification unit ignores said error signal if said reference-picture modification unit has already received an identical error signal from said decoding apparatus.
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43. The coding apparatus of claim 32, further comprising a reference-relationship memory storing information indicating reference relationships used in coding said pictures, wherein:
said reference-picture modification unit refers to the information stored in said reference-relationship memory.
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44. The coding apparatus of claim 32, further comprising an error propagation decision unit determining which parts of said reference picture have been affected by said decoding error by distinguishing between major error propagation effects and minor error propagation effects, and giving the major error propagation effects greater priority than the minor error propagation effects.
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45. A decoding apparatus as described in claim 13, comprising:
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a decoding unit decoding said coded data and detecting. said decoding error;
a error-signal transmission unit coupled to said decoding unit, transmitting said error signal to said coding apparatus;
a reference-picture memory coupled to said decoding unit, temporarily storing each picture decoded by said decoding unit for reference in subsequent decoding; and
a reference-picture modification unit coupled to said reference-picture memory, modifying said reference picture in said reference-picture memory.
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46. The decoding apparatus of claim 45, wherein said reference-picture modification unit determines said part of said reference picture by taking error propagation into consideration.
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47. The decoding apparatus of claim 45, wherein said reference-picture modification unit modifies said reference picture by replacing data affected by said decoding error with data from said reference picture not affected by said decoding error.
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48. The decoding apparatus of claim 45, wherein said reference-picture modification unit modifies said reference picture by replacing data affected by said decoding error with data taken from a previous one of the pictures in said series.
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49. The decoding apparatus of claim 45, wherein said error-signal transmission unit also sends said coding apparatus information describing a procedure by which said reference-picture modification unit modifies reference picture.
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50. The decoding apparatus of claim 45, further comprising an end-information receiving unit receiving information from said coding apparatus indicating that said coding apparatus has modified said reference picture, wherein said reference-picture modification unit modifies each decoded picture stored in said reference-picture memory from detection of said decoding error until said end-information receiving unit 208 receives said information from said coding apparatus.
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51. The decoding apparatus of claim 50, wherein said reference-picture modification unit interprets the information received by said end-information receiving unit as applying both to said decoding error and to any decoding error, detected before said decoding error, for which said end-information receiving unit has not received information from said coding apparatus.
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52. The decoding apparatus of claim 50, wherein said end-information receiving unit, after receiving said information once from said coding apparatus, ignores identical information received later from said coding apparatus.
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53. The decoding apparatus of claim 45, wherein said error-signal transmission unit sends said error signal to said coding apparatus repeatedly.
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54. The decoding apparatus of claim 45, further comprising a reference-relationship memort storing information indicating reference relationships used in decoding said coded data, wherein said reference-picture modification unit refers to the information stored in said reference-relationship memory.
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55. The decoding apparatus of claim 45, further comprising an error propagation decision unit determining which parts of said reference picture have been affected by said decoding error by distinguishing between major error propagation effects and minor error propagation effects, and giving the major error propagation effects greater priority than the minor error propagation effects.
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56. The decoding apparatus of claim 45, further comprising an error concealment unit performing error concealment in the pictures decoded by said decoding unit from detection of said decoding error until said reference picture is modified.
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57. The decoding apparatus of claim 56, further comprising a concealed-error reference-picture memory storing the pictures processed by said error concealment unit, wherein said decoding unit refers to the pictures stored in said concealed-error reference-picture memory, and said reference-picture modification unit copies modified parts of said second modified reference picture from said reference-picture memory to said concealed-error reference-picture memory.
Specification