pre-multiplied alpha when running in overlay mode?

[rmoriz]

Hi,

I'm using --generate overlay to generate overlay-only clips which I then use in my video editing software of choice (DaVinci Resolve) to combine with the actual footage. I'm using the default coloring option values (no bg options specified, I assume it's 0,0,0,0) and the following XML layout for the map:

 <component type="moving_map" name="moving_map" x="3000" y="20" size="800" zoom="17" corner_radius="25" opacity="0.8"/>

It works quite well to strip out the background when using the "LumaKeyer" tool but fails when using the simple clip attribute "alpha mode: premultiplied". I assume that using the "pre-multiplied alpha" would render much faster than using the LumaKeyer which takes a long time to render out.

Sadly I see nasty artefacts not only in the map area but also in texts when using "alpha mode: premultiplied":

As far as I understand, Pillow/PIL has basic support for premultiplied modes: LA (L with alpha), RGBa (true color with premultiplied alpha. However I've not yet tested it. Maybe I'm completely wrong.