[FFmpeg-devel] pixel format convertion yuv422p->yuv420p->yuv411p->yuv422p degrade picture
Tue Jul 15 18:29:59 CEST 2008
Michael Niedermayer wrote:
> On Tue, Jul 15, 2008 at 04:22:33PM +0100, M?ns Rullg?rd wrote:
>> Maksym Veremeyenko wrote:
>> > Dear Developers!
>> > I was testing pixel format changing and found that convertions like:
>> > yuv422p->yuv420p->yuv411p->yuv422p
>> > degrade picture - it become greener.
>> > To prove this i did a shell script, see attached. On 50th iteration
>> > picture is almost compleately green.
>> > Is it normal behaviour for pixel format converting or it is a bug?
>> Apparently, rounding errors in the chroma interpolation are accumulating.
>> Without thinking a little harder, I don't know whether such a conversion
>> sequence is possible without such drift. It will always be lossy, as I'm
>> sure you already realise.
> Its possible in principle without the drift, one example that does not drift
> would be nearest neighbor convertion.
Yes, of course. I should have been specific using correct (or decent)
> I suspect that dithering could reduce the drift, for normal interpolation
> based filters
Possibly. However, I doubt it's worth the effort, since as you say...
> but running 50 converters in a row is a stupid thing to do.
... and that I can agree with.
mans at mansr.com
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