[FFmpeg-devel] pixel format convertion yuv422p->yuv420p->yuv411p->yuv422p degrade picture

[Siarhei Siamashka]

On Tue, Jul 15, 2008 at 7:35 PM, Maksym Veremeyenko wrote:
> Michael Niedermayer ???????(??):
>> On Tue, Jul 15, 2008 at 04:22:33PM +0100, M?ns Rullg?rd wrote:
> [...]
>>> 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.
> I did cyclic test for:
>
>  +->422->420->422->411->422-->+
>  |                            |
>  +----------------------------+
>
> no visial degrades found.
>
>> I suspect that dithering could reduce the drift, for normal interpolation
>> based filters but running 50 converters in a row is a stupid thing to do.
> Such condition possible in:
> Uncompressed (4:2:2) -> DV25 (4:2:0) -> DVCpro25 (4:1:1) -> Uncompr
>
> 50 iterations was only for proving that convertions degrade picture...
>
> So, as conclusion, that a normal?

In my opinion it's a bit suspicious and may need an investigation to
understand what happens.

Can you try to find a shorter chain of conversions which results in
this effect (preferably a conversion between two formats). Also what
happens if you run tests with an image, uniformly filled with some
color? Does it also degrade to green?