[Kdenlive-devel] Color spaces and MLT

[Simon Eugster]

2010/8/14 Dan Dennedy <dan at dennedy.org>:
> 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.

By the way, I changed the Histogram and the Waveform to use Rec. 709
by default (can be changed in the context menu). They look much
smoother now.  :)

Simon