On Tue, 24 May 2005, Dik Takken wrote:
> I recently switched from yuvscaler to y4mscaler for reasons known to
> some of you ;) and came across a problem: The croma data in the image
> that has been processed via y4mscaler looks weird. I compared the
> output of the command
>
> smil2yuv -i 2 test.dv | y4mscaler -O chromass=420_MPEG2 -S option=sinc:4 |
> yuvcorrect -Y LUMINANCE_1.0_16_235_127_127 -Y
> CHROMINANCE_0.0_4_128_4_128_16_240 | yuvplay
>
> smil2yuv test.dv | yuvcorrect -Y LUMINANCE_1.0_16_235_127_127 -Y
> CHROMINANCE_0.0_4_128_4_128_16_240 | yuvplay
>
> The difference is attached to this mail. I tried playing with the -S
> option of y4mscaler, but I did not manage to get a decent picture.
The -S option isn't critical - a higher number of taps would preserve
a slightly higher level of detail but wouldn't make a huge difference.
> What is it that I'm doing wrong?
Using "-i 2" with smil2yuv.
From smil2yuv's usage summary:
Usage: smil2yuv [ -i type ] [ -a audio-file ] file [ file ... ]
Where: file is smil, dv avi (1 or 2) or raw dv
-i type - 0 no deinterlacing, 1 bad deinterlacing
2 experimental 4:1:1 subsampling (more to follow)
"2" means 4:1:1 - and I thought you were dealing with PAL DV which is
one of the 4:2:0 variants.
I think that "-i 2" is forcing smil2yuv to treat PALDV data as 4:1:1
rather than 4:2:0. The result will be rather severe misalignment of
the chroma planes ;)
That's my theory at the moment.
What happens if you combine the two commands above into:
smil2yuv test.dv | \
y4mscaler -O chromass=420_MPEG2 -S option=sinc:4 | \
yuvcorrect -Y LUMINANCE_1.0_16_235_127_127 -Y
CHROMINANCE_0.0_4_128_4_128_16_240 | yuvplay
4:1:1 frames and 4:2:0 frames occupy the same amount of space so it's
possible to feed 4:1:1 data into a program expecting 4:2:0 and no
crash will happen. But you'll get "special effects" type of colors ;)
Cheers,
Steven Schultz
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