Image re-encoding method to decode image data which is orthogonally transformed per first block and encoded by a first encoding method
Provided is an image re-encoding method which simultaneously satisfies reduction of block distortion and reduction of a memory when re-encoding image data encoded by a first encoding method, by a second encoding method. An image re-encoding method comprises the steps of decoding image data encoded per block by the first encoding method; and encoding the image data decoded in the step of decoding, per block by the second encoding method. The step of encoding the image data includes the steps of: performing boundary detection to detect a block boundary of the image data encoded by the first encoding method, with the use of the image data encoded by the first encoding method; and deblocking to perform a deblocking filter process to the block boundary detected in the step of performing boundary detection.
1. An image re-encoding method to decode image data which is orthogonally transformed per first block and encoded by a first encoding method with an encoded block unit of a plurality of first orthogonal transform blocks, and to encode the decoded image data per second block by a second encoding method, the image re-encoding method comprising the steps of:
performing first deblocking filtering to perform a deblocking process to a block boundary bordered by a first orthogonal transform block in an encoded block in the second encoding; and
encoding the second block by determining the first deblocking filter strength with the use of the image data, and by changing second deblocking filter strength to an encoded block boundary of the first encoding method in accordance with the first deblocking filter strength.
2. The image re-encoding method according to claim 1 ,
wherein the image data includes picture type information and macroblock type information as encoding parameters for the first encoding method, and
wherein the first deblocking filter strength is enhanced when the picture type is an intra picture or when the macroblock type is an intra type.
3. The image re-encoding method according to claim 2 ,
wherein the image data includes DCT type information as an encoding parameter information for the first encoding method, and
wherein the first deblocking filter strength is enhanced when the DCT type is a frame type.
4. The image re-encoding method according to claim 2 ,
wherein the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the first deblocking filter strength to a block boundary in the horizontal direction of the first encoding method is enhanced when the DCT type is a field type.
5. The image re-encoding method according to claim 2 ,
wherein the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the image re-encoding method further includes the steps of:
enhancing the first deblocking filter strength to a block boundary in the first encoding method when the DCT type is a frame type; and
enhancing the first deblocking filter strength to a horizontal boundary of a block in the first encoding method when the DCT type is a field type.
6. The image re-encoding method according to claim 2 ,
wherein the first encoding method includes the step of calculating activity information indicative of degree of complexity of an image per orthogonal transform block, and
wherein, when the activity is less than a threshold, the first deblocking filter strength is enhanced.
7. The image re-encoding method according to claim 2 ,
wherein the first encoding method includes the step of calculating activity information indicative of degree of complexity of an image per orthogonal transform block,
wherein, when the activity is less than a threshold, the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the first encoding method further includes the steps of: enhancing the first deblocking filter strength to a block boundary of the first encoding method when the DCT type is a frame type; and enhancing the first deblocking filter strength to a horizontal boundary of a block in the first encoding method when the DCT type is a field type.
8. The image re-encoding method according to claim 1 ,
wherein the image data includes quantization scale information as an encoding parameter for the first encoding method, and
wherein the first deblocking filter strength is enhanced as much as the quantization scale is coarse.
9. The image re-encoding method according to claim 1 ,
wherein the image data includes picture type information, macroblock type information, and quantization scale information as encoding parameters for the first encoding method, and
wherein the first deblocking filter strength is enhanced as much as the quantization scale is coarse when the picture type is an intra picture or when the macroblock type is an intra type.
10. An image re-encoding device to decode image data which is orthogonally transformed per first block and encoded by a first encoding method with an encoded block unit of a plurality of first orthogonal transform blocks, and to encode the decoded image data per second block by a second encoding method, the image re-encoding device comprising:
first deblocking filter unit operable to perform a deblocking process to a block boundary bordered by a first orthogonal transform block in an encoded block in the second encoding; and
encoding unit operable to encode the second block by determining the first deblocking filter strength with the use of the image data, and by changing the second deblocking filter strength to an encoded block boundary of the first encoding method in accordance with the first deblocking filter strength.
11. The image re-encoding device according to claim 10 ,
wherein the image data includes picture type information and macroblock type information as encoding parameters for the first encoding method, and
wherein the first deblocking filter strength is enhanced when the picture type is an intra picture or when the macroblock type is an intra type.
12. The image re-encoding device according to claim 11 ,
wherein the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the first deblocking filter strength to a block boundary in the horizontal direction of the first encoding method is enhanced when the DCT type is a field type.
13. The image re-encoding device according to claim 11 ,
wherein the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the image re-encoding device further comprises
enhancement unit operable to enhance the first deblocking filter strength to a block boundary in the first encoding method when the DCT type is a frame type; and
enhancement unit operable to enhance the first deblocking filter strength to a horizontal boundary of a block in the first encoding method when the DCT type is a field type.
14. The image re-encoding device according to claim 11 ,
wherein the first encoding method includes activity calculation unit operable to calculate activity information indicative of degree of complexity of an image per orthogonal transform block, and
wherein, when the activity is less than a threshold, the first deblocking filter strength is enhanced.
15. The image re-encoding device according to claim 11 ,
wherein the first encoding method includes activity calculation unit operable to calculate activity information indicative of degree of complexity of an image per orthogonal transform block,
wherein, when the activity is less than a threshold, the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the first encoding method further includes enhancement unit operable to enhance the first deblocking filter strength to a block boundary of the first encoding method when the DCT type is a frame type, and operable to enhance the first deblocking filter strength to a horizontal boundary of a block in the first encoding method when the DCT type is a field type.
16. The image re-encoding device according to claim 10 ,
wherein the image data includes quantization scale information as an encoding parameter for the first encoding method, and
wherein the first deblocking filter strength is enhanced as much as the quantization scale is coarse.
17. The image re-encoding device according to claim 10 ,
wherein the image data includes picture type information, macroblock type information, and quantization scale information as encoding parameters for the first encoding method, and
wherein the first deblocking filter strength is enhanced as much as the quantization scale is coarse when the picture type is an intra picture or when the macroblock type is an intra type.
18. The image re-encoding device according to claim 10 ,
wherein the image data includes DCT type information as an encoding parameter for the first encoding method, and
wherein the first deblocking filter strength is enhanced when the DCT type is a frame type.
19. An image re-encoding program product, embodied on a non-transitory computer-readable medium, to make a computer execute an image re-encoding method to decode image data which is orthogonally transformed per first block and encoded by a first encoding method with an encoded block unit of a plurality of first orthogonal transform blocks, and to encode the decoded image data per second block by a second encoding method, the image re-encoding method comprising the steps of:
performing first deblocking filtering to perform a deblocking process to a block boundary bordered by a first orthogonal transform block in an encoded block in the second encoding; and
encoding the second block by determining the first deblocking filter strength with the use of the image data, and by changing second deblocking filter strength to an encoded block boundary of the first encoding method in accordance with the first deblocking filter strength.
20. The image re-encoding program product according to claim 19 ,
wherein the image data includes picture type information and macroblock type information as encoding parameters for the first encoding method, and
wherein the first deblocking filter strength is enhanced when the picture type is an intra picture or when the macroblock type is an intra type.
21. The image re-encoding program product according to claim 20 ,
wherein the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the first deblocking filter strength to a block boundary in the horizontal direction of the first encoding method is enhanced when the DCT type is a field type.
22. The image re-encoding program product according to claim 20 ,
wherein the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the image re-encoding method further includes the steps of:
enhancing the first deblocking filter strength to a block boundary in the first encoding method when the DCT type is a frame type; and
enhancing the first deblocking filter strength to a horizontal boundary of a block in the first encoding method when the DCT type is a field type.
23. The image re-encoding program product according to claim 20 ,
wherein the first encoding method includes the step of calculating activity information indicative of degree of complexity of an image per orthogonal transform block, and
wherein, when the activity is less than a threshold, the first deblocking filter strength is enhanced.
24. The image re-encoding program product according to claim 20 ,
wherein the first encoding method includes the step of calculating activity information indicative of degree of complexity of an image per orthogonal transform block,
wherein, when the activity is less than a threshold, the image data includes DCT type information as encoding parameter information for the first encoding method, and
wherein the first encoding method further includes the steps of: enhancing the first deblocking filter strength to a block boundary of the first encoding method when the DCT type is a frame type; and enhancing the first deblocking filter strength to a horizontal boundary of a block in the first encoding method when the DCT type is a field type.
25. The image re-encoding program product according to claim 19 ,
wherein the image data includes quantization scale information as an encoding parameter for the first encoding method, and
wherein the first deblocking filter strength is enhanced as much as the quantization scale is coarse.
26. The image re-encoding program product according to claim 19 ,
wherein the image data includes picture type information, macroblock type information, and quantization scale information as encoding parameters for the first encoding method, and
wherein the first deblocking filter strength is enhanced as much as the quantization scale is coarse when the picture type is an intra picture or when the macroblock type is an intra type.
27. The image re-encoding program product according to claim 19 ,
wherein the image data includes DCT type information as an encoding parameter information for the first encoding method, and
wherein the first deblocking filter strength is enhanced when the DCT type is a frame type.