lift/gamma/gain - Color adjustment - 2 issues, maybe related to each other.
Issue 1: When the slider on "Lift" is on it's "0" position, moving around the color selector does not have any effect.
However, if you move the slider to any value that is not 0, moving the color selector around does have an effect on the color of the shadows.
It would seem to me that the color selector should have an effect no matter where the intensity slider is positioned.
Issue 2: When the slider is positioned away from 0, and a color adjustment is made, the color adjustment is re-set if the slider is dragged to 0, or slowly past 0.
Playing around with the effect, I can see that Gamma and Gain also reset their color adjustment when their slider reaches 0. The big difference is that the range for Gamma and Gain is 0 to 2 and 0 to 4 respectively, while for lift the range is -1 to 0 to 1.
In my humble opinion, the color adjustment in Lift, Gamma and Gain should not be reset unless specifically requested by the user.
Reading through the documentation for this effect in MLT, I am a little mystified. It states that the minimum value for lift is 0, and in Kdenlive we are able to do -1. How is that possible? Could this be the reason that this effect misbehaves?
The documentation also only mentions red, green and blue values, so it would appear that the slider is some sort of mechanism to adjust all the channel values at once, and is internal to Kdenlive. I have a gut feeling that the slider position is multiplied with the channel values, which is why it zeros out the color adjust at 0.
Let's say that when you select a color offset, you adjust the ratio between red, green and blue. This is a ratio that must be preserved whatever the intensity the slider is set at. If anywhere in the equation you are multiplying the slider value with the red, green, and blue, that ratio between red, green and blue will be removed if the slider value is 0, because anything multiplied by 0 is 0.
It might be an idea to have the slider values only as a range of positive integers, and then translate that to a percentage to be added or taken away from the actual red, green and blue channels to avoid the trap of multiply by 0.