Image encoder, image decoder, and image encoding system

• US 20100074331A1
• Filed: 06/17/2009
• Published: 03/25/2010
• Est. Priority Date: 09/25/2008
• Status: Active Grant

• Current Assignee: OKI Electric Industry Company Limited
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Nishi, Takashi
• Granted Patent: US 8,218,652 B2
• Time in Patent Office: Days
• US Class Current: 375/240.120
• CPC Class Codes: H04N 19/105 Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
• CPC Class Codes: H04N 19/166 concerning the amount of transmission errors, e.g. bit error rate [BER]
• CPC Class Codes: H04N 19/507 using conditional replenishment
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

An image coding system includes an image encoder and a predictive image decoder. The image encoder encodes an input image to obtain encoded data, compares the input image with a reference image, generates error information identifying parts of the input image that are changed with respect to the reference image, and outputs the encoded data and the error information. The predictive image decoder predicts the image, using a simplified prediction method for parts of the image identified by the error information as not being changed, and decodes the encoded data and the predicted data to obtain decoded image data. Use of the simplified prediction method in unchanged parts of the image reduces the prediction processing load without significant loss of prediction accuracy.

Claims

1. An image encoder comprising:

an encoding unit for encoding an input image to obtain encoded data;

a comparison unit for comparing the input image with at least one reference image to identify a part of the input image that is significantly changed with respect to the at least one reference image;

an information generating unit for generating error information identifying the changed part identified by the comparison unit; and

an output unit for outputting the encoded data and the error information.

2. The image encoder of claim 1, wherein the at least one reference image and the input image are images in a video sequence.

3. The image encoder of claim 1, wherein the at least one reference image is another image input to the image encoder.

4. The image encoder of claim 1, wherein the comparison unit predicts the at least one reference image from at least one preceding and/or following image input to the image encoder.

5. The image encoder of claim 1, wherein the information generating unit divides the input image into bit planes and identifies image blocks in each bit plane that have bit values differing in at least fifty percent of bit positions from bit values in the at least one reference image.

6. The image encoder of claim 1, wherein the encoding unit performs Slepian-Wolf encoding.

15. An image coding system including the image encoder of claim 1 and an image decoder, the image decoder comprising:

a receiving unit for receiving the encoded data and error information output by the image encoder;

a prediction unit for generating predicted values of decoded image data, using a first prediction process in the changed part identified by the error information and a second prediction process in image parts other than the changed part, the first prediction process being more computationally intensive than the second prediction process; and

a decoding unit for decoding the encoded data and the predicted values to obtain the decoded image data.

16. The image coding system of claim 15, wherein the prediction unit searches for motion vectors, and the first prediction process has a larger search range than the second prediction process.

17. The image coding system of claim 15, wherein:

the encoding unit performs Slepian-Wolf encoding; and

the decoding unit performs Slepian-Wolf decoding.

18. An image coding system including the image encoder of claim 1 and an image decoder, the image decoder comprising:

a receiving unit for receiving the encoded data and the error information output by the image encoder;

a prediction unit for generating predicted values by predicting a result of decoding the encoded data;

a prediction revision unit for revising the predicted values in the changed part identified by the error information to obtain revised predicted values; and

a decoding unit for decoding the encoded data, the revised predicted values, and the predicted values that the prediction revision unit did not revise, thereby obtaining decoded image data.

19. The image coding system of claim 18, wherein:

the comparison unit in the image encoder also generates the predicted values by predicting the result of decoding the encoded data;

the error information identifies a part of the encoded data in which the input image encoded by the image encoder has bit values differing in at least fifty percent of bit positions from the predicted values; and

the prediction revision unit revises the predicted values by inverting the bit values.

20. The image coding system of claim 18, wherein:

the encoding unit performs Slepian-Wolf encoding; and

the decoding unit performs Slepian-Wolf decoding.

7. An image decoder for decoding an encoded image, comprising:

a receiving unit for receiving encoded data representing an image and error information identifying a changed part of the image;

a prediction unit for generating predicted values of the image by using a first prediction process in the changed part of the image and a second prediction process in parts of the image other than the changed part, the first prediction process being more computationally intensive than the second prediction process; and

a decoding unit for decoding the encoded data and the predicted values to obtain decoded image data.

8. The image decoder of claim 7, wherein the error information identifies a part of the encoded image that is changed with respect to at least one reference image, and the prediction unit generates the predicted values from the at least one reference image.

9. The image decoder of claim 8, wherein the at least one reference image and the encoded image are images in a video sequence.

10. The image decoder of claim 7, wherein the prediction unit searches for motion vectors, and the first prediction process has a larger search range than the second prediction process.

11. The image decoder of claim 7, wherein the decoding unit performs Slepian-Wolf decoding.

12. An image decoder for decoding an encoded image, comprising:

a receiving unit for receiving encoded data representing an encoded image and error information identifying a changed part of the encoded image;

a prediction unit for generating predicted values by predicting a result of decoding the encoded image;

a prediction revision unit for revising the predicted values in the changed part of the encoded image; and

a decoding unit for decoding the encoded data, the revised predicted values in the changed part of the encoded image, and the predicted values in parts of the encoded image other than the changed part, thereby obtaining decoded image data.

13. The image decoder of claim 12, wherein the prediction revision unit revises the predicted values by inverting bit values.

14. The image decoder of claim 12, wherein the decoding unit performs Slepian-Wolf decoding.