which one is the most successful scheme to reduce blocky artifacts in low bit rate JPEG image?

walala wrote:
> 
> Anybody give me some pointers? Thanks a lot in advance!

The best way to reduce blocking artifacts in low bit rate JPEG is
scaling down the image when compressing and scaling up when
decompressing with the new cjpeg/djpeg scaling options:

  http://jpegclub.org/cjpeg/
  http://jpegclub.org/djpeg/

For example, I did a test with a highly compressed (cjpeg -q 8...20)
JPEG image which looked quite blocky.  If you use cjpeg -scale 1/2,
you can go up to q=60 for the same compressed filesize, nearly
removing the blocking artifacts.  You can use djpeg -scale 2/1
to decode that image back to the source resolution.

Regards
Guido

Hey, that's a good idea! At low bit rates, that 8x8 block size is just too
small.

Matt Timmermans wrote:
> 
> Hey, that's a good idea! At low bit rates, that 8x8 block size is just too
> small.

Yes, the new code uses a 16x16 FDCT and IDCT instead of 8x8 for the cjpeg
1/2 and djpeg 2/1 scalings.  That seems to work quite well and efficient. 

Regards
Guido