Creating a video from an image sequence with alpha values

Hey guys :slight_smile:

I rendered a little smoke animation in Blender v2.72 whereas the background is transparent and the smoke has a very low density. I chose to render single PNG images as I had some troubles with the OpenGL Renderer (I had to edit every image with photoshop to make it look nice ans smooth).

Now my 600 PNG images look perfectly nice and I want to put them together in an image sequence. I tried using the Blender video sequence editor but it fills in every alpha value with black. I want to put this smoke simulation over another external video sequence so it has to be transparent except for the smoke.

How do I accomplish that?

Thanks,
Choix :slight_smile:

Not sure because I didn’t really use VSE but I think it should work like this:

  • put the external clip on a lower track then the image sequence (like you’d do with any other video editor)
  • select the image sequence
  • open the properties side panel (N-key) and under Edit Strip, change the blend mode to Alpha over

HTH :slight_smile:

Why convert it to video in the first place? The VSE can input image sequences.

Steve S

As far as I know, there aren’t many video formats that support transparency. One is Apple Prores 4444, but I’ve had only limited and mixed results getting anything into that format with the alpha channel intact, even using Apple compressor, or Adobe Media Encoder. The only successful exports I’ve done I think are using Apple Motion to compile the image sequence and exporting from that programme, and eve then, that seems to introduce some colour shift…

A simpler option may be to just render your smoke with a black background, then composite or layer the smoke using an Add blend mode. or maybe Screen if that looks better.

Good luck.

Or render a separate alpha channel pass as a sync video stream. Then use both together, one as an alpha mix input. Other alternative is to try and export with legacy Quicktime Animation codec, it does support alpha.

Ah yeah, I forgot about the Animation codec. Used to use it all the time… another useful thing Apple did, then decided to take away from us. :slight_smile: