I shot a bird in my backyard. As it flies from tree to tree it becomes difficult to see it because the background is only vegetation. I'd like to "enhance" the bird by making it "brighter" against the background, i.e. by turning the surrounding area "darker". For example, when a TV shots a police chase, the vehicle being followed becomes distinguished (or "brighter") from the others (that become "darker"). Is this possible in Kdenlive? What's the technical term that defines this effect?
You could use rotoscope. You put two copies of the footage on the time line one on track 1 and the other on track 2. You brighten the one on track 2 up and darken the one on track 1 down. You add a composite transition between the two. And then you add rotoscope and draw rotoscope paths around your bird at key frames. The rotoscope allows track 2 to show through brighting up around the bird.
You need to make a selection in the alpha channel.
From what you say, I guess the bird is quite similar color-wise to the background, and chroma keying won't work well.
So, if you want an more or less exact outline of the bird, the only solution would be manual rotoscoping, for each frame separately!
If you just want to put a "spotlight" on the bird, you can use alpha shapes, and just keyframe the position of the spot.
After you have obtained an alpha mask by any of the above methods, put a copy of the same video on a track below, make it brighter, and add a composite transition to the top track, so that the brighter video track will show through the "alpha hole", that you placed on the bird in the top track.
OOOps, collided with ttguy... :-)