[transcode-users] chroma subsampling needs to be anti-aliased

[Claude Heiland-Allen]

Hi folks,

I have a large number (46650) of image files that I thought I would use
transcode to convert to DVD MPEG2, seeing that it has an mpeg2enc back end.
But, the output is really really ugly - it seems the chroma subsampling
is spatially aliased, so my 1-pixel lines flicker between colour and
grey in a very wrong way:

http://claudiusmaximus.goto10.org/test/video/bad.png

Compare with this:

http://claudiusmaximus.goto10.org/test/video/good.png

and you can see that:

(good)   lossless TIFF images -> ppm -> ppmtoy4m -> mpeg2enc -> MPEG2

is vastly superior to:

(bad)    lossless TIFF images -> transcode -> mpeg2enc -> MPEG2

Any thoughts?

Would it be possible to add antialiasing to the subsampled chroma plane
generation?  ppmtoy4m seems to do things correctly.


Claude

((
In the end I used ImageMagick's 'convert' to convert all the images to 
PNG format, and then a home-brew C program to concatenate them all into 
one PPM stream fed into ppmtoy4m, and the results were much better, as 
good as the "good.png" screenshot which used GridFlow to do the 
concatenation.
))

--
http://claudiusmaximus.goto10.org