[Kdenlive-devel] Color spaces and MLT

[Dan Dennedy]

On Wed, Jul 21, 2010 at 10:51 AM, Simon Eugster <simon.eu at gmail.com> wrote:
> Dear friends,
>
> I've just added an RGB parade to kdenlive. While testing I found
> something interesting: Although I'm painting on a rect with height 256
> (as atm we're dealing with 8 bits per channel only) and scaling the
> parade afterwards to the target height, I got kind of scanlines.
> Compare these two images:
> http://granjow.net/uploads/kdenlive/kdenlive-mlt-rgbparade-noeffect.png
> http://granjow.net/uploads/kdenlive/kdenlive-mlt-rgbparade-witheffect.png
> With the MLT effect there are scanlines, without it there are none.
>
> This is quite interesting, as this visualizes how color information
> gets lost when converting between different color spaces (according to
> [1], MLT is using YUV422, the input image is RGB).
>
> Basically I just wanted to show you this because it is interesting.
> But in the long term one of our goals should also be to avoid either
> conversion to other color spaces or the loss of information caused by
> the conversion.

I just pushed some changes in mlt to fix this problem when using
libswscale - at least on my version. It adds some flags, but some
flags are needed for some color/pixfmts and different flags for
others. Use an incorrect flag, and the results are totally disastrous!
So, I am little worried that it might be version-sensitive. It would
be good if you and others could update mlt from git, test it, and see
if this problem resolves for you without introducing disaster.

-- 
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