[Kdenlive-devel] Color correction tools: How and where to implement them?

[Simon Eugster]

I have added a Vectorscope to kdenlive now.
Re-using it in a different project would require only few changes
given that the other project works with Qt as well, it would mainly
mean copying the widget and adjusting some values.
I will look into other color displays now if time allows it (exams in 3 weeks).

2010/7/11 Dan Dennedy <dan at dennedy.org>:
> On Fri, Jul 9, 2010 at 12:29 PM, Simon A. Eugster <simon.eu at gmail.com> wrote:
>> What still needs to be improved:
>> * Curves is not really useful at the moment because of the
>>   chosen interpolation method. For example, this curve is
>>   impossible for now:
>>   http://granjow.net/uploads/kdenlive/gimp-curves.png
>>   Also it is limited to only 3 points, which is not enough
>>   for earnest color correction.
>
> More than likely it was useful to the person who wrote it.

Should be improved nevertheless :)

>> * 3-Way color correction works basically quite well,
>>   but the usability is terrible.
>>   If you want to change the blacks, you have to rise the black
>>   value to see colors in the color picker, and at the end make
>>   it nearly black again. Would be much better to just chose a
>>   color and not having to worry about black.
>>   Also is it not very convenient not to have a live preview.
>
> All Kdenlive effects have live preview. So, a simple enhancement to
> toggle that would help.

Well, there is live preview as soon as the color has changed in the
widget. But this is only the case when the color picker has been
closed already. There should be a built-in color picker.

>> * White balance: You cannot click into a monitor to pick a
>>   neutral color from there.
>
> Yeah, why is that? Is that due to the Qt dialog mode? It would be nice
> to have the "eye dropper" directly in the effects panel instead of
> having to open the dialog.
>
>>   You should also be able to change the color temperature
>>   as this also belongs to white balance.
>
> Internally, the color selection sets the temperature, and I feel most
> people should use it by interactively selecting the color to be
> neutral. I can expose temperature as a parameter, but then I  need a
> way to pass invalid color and temperature values to prevent one
> parameter from clobbering the other. Otherwise, I will need to add
> another parameter to let one choose the defining parameter.

I'm pretty sure it is not the color temperature. The white balance
here changes to magenta for low values, and to green for high values.
It should rather be blue for low temperature, orange for high
temperatures.

> parade and vectorscope are available in frei0r, but they do not make
> sense as general video effects. They require special integration into
> Kdenlive monitor, but it is not implemented yet.

Ah, that's why they don't show up in the effect list anymore. They
used to be there some months ago :)


>>>     What is the current status?
>
> I do not believe digikam/showfoto's image processing or widget code
> exists as a library to facilitate reuse. No one has contributed gegl
> integration into MLT, and I have been working on higher priority
> tasks. Meanwhile, frei0r integration has already addressed many of
> these needs. There is no simple and clean integration that exposes all
> of the capabilities of one these other tools. You can, however, export
> a series of stills (Kdenlive could make this easier) and process them
> with the Gimp Animation Plugin or blender and then load the result of
> that as a clip.

Okay.

>>>     The point is also, I would like to do it interactively. Means, if I
>>>     e.g. have a levels display[1] I would like to be able to select the
>>>     lower 25 % of the curve (all dark pixels) and have them highlighted in
>>>     the kdenlive project monitor. So I guess neither frei0r nor MLT would
>>>     be suitable for that at the moment? (I don't know MLT yet, and frei0r
>>>     only partially) Could MLT probably be extended this way, or is this
>>>     not intended?
>
> The frei0r filters that apply need to be enhanced to support that, or
> the way frei0r is integrated into MLT could be enhanced to support
> that for all filters (currently, the MLT frei0r module acts as a
> simple bridge between MLT and frei0r). At that point you have only
> addressed the image processing pipeline and not any UI. Any UI change
> would need to be done in Kdenlive as that does not exist in MLT or
> frei0r.

At the moment the second option sounds quite good to me. This would
not require applying a frei0r effect (e.g. for the vectorscope I wrote
for kdenlive) to a clip to get the highlighting, if I understand
correctly.