1. 1 An Efficient Method for DCT- Domain Image Resizing with Mixed Field/Frame-Mode Macroblocks Changhoon Yim and Michael A. Isnardi IEEE TRANSACTION ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 9, NO. 5, AUGUST 1999

2. 2 Outline Introduction DCT-Domain Image Resizing Decomposition of DCT-Domain Image Resizing Operation Proposed DCT-Domain Image Resizing Method Discussion on DCT-Domain Filtering Experimental Result Conclusion

3. 3 Introduction Many image and video compression standards such as JPEG, MPEG-1, MPEG-2, and H.261 are based on DCT coding techniques. In MPEG-2, there are field and frame pictures to accommodate coding of progressive and interlaced video. Previous DCT-domain image resizing methods assume that all macroblocks are in the frame mode.

4. 4 Field and frame mode of a macroblock in the spatial domain

5. 5 DCT-Domain Image Resizing : Four Steps Low-pass filtering in the DCT domain Inverse DCT 2 : 1 downsampling Forward DCT

6. 6 DCT-Domain Image Resizing : Matrices DCT transform matrix Downsampling matrix Low-pass filter

7. 7 Decomposition of DCT-Domain Image Resizing Operation

8. 8 Inverse DCT for a DCT block

9. 9 Downsampling in the spatial domain

10. 10 Proposed DCT-Domain Image Resizing Method

11. 11 Frame- and Field-mode resizing transformation matrices

12. 12 Discussion on DCT-Domain Filtering (1) Previous methods are simple low-pass filtering by truncation in DCT domain The matrix is not equivalent to sharp low-pass filter in DFT domain, and dose not correspond to a liner convolution in the spatial domain May produce visible aliasing and blocking artifacts Affect differently the field- and frame-mode in spatial domain may result in serious blocking artifacts between field- and frame-mode macroblocks

13. 13 Discussion on DCT-Domain Filtering (2) The implicit low-pass filtering operation as averaging by the downsampling matrices would be a good compromise for block-based DCT-domain image resizing Would not have any blocking artifact The filtering characteristics should be the same for field- and frame-mode macroblocks

14. 14 Experimental Results (1)

15. 15 Experimental Results (2)

16. 16 Experimental Results (3)

17. 17 Conclusion Propose method can handle field-mode Avoid the blocking artifacts and the difference in the characteristics between field- and frame-mode macroblocks Future research could be performed for more efficient for low-pass filtering in the DCT domain for DCT-domain image resizing