Banding artifact of h.264???

[Manao]

You have to force ffdshow to output RGB (disable any other kind of output), and to enable "high quality yv12 to rgb conversion". In avisynth, chroma downsampling isn't good, whatever the conversion.

[10L23r]

k, i figured out the ffdshow thing, thx

so when converting rgb to 4:2:0, does it help to manually downsample the chroma? (i.e. converttoyv24, resize chroma, mergechroma...)

There are several reasons, all more or less occurring at the same time :
- you convert to yv12, so Y = round(aR + bG + cB). So you might end up with 0 1 1 3 4 5 7 7 instead of 0 1 2 3 4 5 6 7 for Y
- in order to show it on your screen, you have to convert back to RGB. The first problem might occur again


i think those are the two main reasons. if you open the second image in an image editor and compare the colors of adjacent pixels in different bands, the difference is two. and each band is not one specific color.

[drpaulng]

After reading a lot of materials about the 8bit down-conversion. I see that many authors wrote with different (mis-)concepts about the present broadcast standard 8bit 4:2:0 video format. I am trying not to make more confusion by stating the fact and conclude for this thread now.

According to HDTV standard ITU-R Recommendation BT.709, of the 8bit (full 0-255), Black and white values are limited to 16-235 (luma) while color values are limited to 16-240 (chroma), the same as the old SDTV standard ITU Rec. 601. However, the forumula for RGB-to-YCrCb 4:2:0 conversion has different correction constants for Rec. 601 (old TV set), and Rec. 709 (new HDTV set) with different gamma correction characteristics.

REFERENCE: http://en.wikipedia.org/wiki/YCbCr

The main reason of banding is caused by truncated values of bit-depth...just like 24bit music is down-converted to 16bit. When a lot of near-the-same values are grouped together - they tend to be flattened in groups (loss of sound or color details). This happens before further compression such as ac3/dts(audio) or mpeg2/avc(video) is applied.