Applying a video effect only to a certain region of the video

Hello,

I'd like to ask if it's possible to apply a video effect only to a certain region of the video. For example a certain region may need a change in brightness whereas the rest may be OK.

Apparently this is possible the Obscure effect (square regions only), but is there a generic technique for the other effects?

Cheers

You could chop a video clip into as many pieces as you want and apply the effect only to the pieces that need it.

@tidris769

He obviously means a specific region of a clip (as in... in the frames)... not a time in a clip (what you're thinking of).

You can add the clip twice on two tracks on top of each other, then crop the clip on the top (using the crop effect, not changing its length), apply the effect to the clip on top and composite it on the clip below.
There recently also has been work to apply effects only to a region defined by a image (or clip), but I think this is not working correctly yet and also only available in the development version.

@till

Does the crop effect work for the described purpose, ie masking a region of the video?

In my tests the crop effect is zooming the video, so defeating that purpose. Please look at the attached screenshots.

Original file attached.

Cropped file attached.

I also tried Scale0tilt (which is able to "hide" all but a square of the video) and Vignette (which masks all except a circle whose edges can be smoothed). The problem with both is that the effect (ex: Brightness) also gets applied to the surrounding black region generated by the effect. This defeats the purpose of having the effect restricted to a certain region and will mess the compositing.

Comments?

I am working on an "alpha controlled" color manipulation Frei0r plugin. Will affect the image proportionally to the alpha channel.

Correcting myself: although with scale0tilt the effect also gets applied to the black surroundings it seems to work with the composite transition after all. But I had no luck the Vignette. The behavior seems to be inconsistent, so I opened this bug report:

http://www.kdenlive.org/mantis/view.php?id=1725

@Marko: I see roughly your idea, but I don't know how it can help this situation. I need to be able to select a certain region of the clip. I don't know if I can control the alpha channel or if all the videos come with an alpha channel.

I also plan a few plugins for alpha manipulation, like filling spots and gradients, this could be more or less what you need...