[Kdenlive-devel] Color spaces and MLT

[Simon A. Eugster]

On 22.07.2010 22:57, Dan Dennedy wrote:
> On Thu, Jul 22, 2010 at 12:09 PM, Simon Eugster<simon.eu at gmail.com>  wrote:
>> 2010/7/21 Dan Dennedy<dan at dennedy.org>:
>>> On Wed, Jul 21, 2010 at 12:16 PM, Simon Eugster<simon.eu at gmail.com>  wrote:
>>>> 2010/7/21 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).
>>>>>
>>>>> It does not operate exclusively in YUV422. The color/image-format
>>>>> conversion implementation depends on your build and your version of
>>>>> libswscale (>= 0.7.2) whether MLT uses libswscale or inbuilt routines.
>>>>> Maybe the problem is in the composite transition.
>>>>
>>>> libswscale is at 0..6 here in debian sid.
>>>
>>> I do not believe that is correct. Maybe you are looking at a package
>>> version. What does 'ffmpeg -version' show as the libswscale version?
>>
>> Something different.
>>   libswscale     0.11. 0 /  0.11. 0
>>
>
> So your MLT should be using libswscale for colorspace and image format
> conversion as well as scaling. This is generally a good thing.

By the way, what happens when rendering to a file? If the input is in RGB, 
and no filters/effects operating in YUV only are put on top of it, will it 
remain RGB until being written to the output file?

Simon