Emmissive material loses colour/brightness when rendered against transparent

Artistic Support Materials and Textures
1

As the title says really…

Here is a section of the image rendered without ‘transparent’ set in the film options:


and is a section of the image rendered with ‘transparent’ set in the film options, with a black background added in photoshop:


as you can see they particles hardly render at all against the transparent background, and have pretty much no colour.

Is there any way around this?

2

Upload a sample image and/or blend file. I would guess it is a problem on double-premultiplication of rgb channels. Do a little test and switch the black background for a light gray or colored in photoshop and see if objects get an unnatural dark edge.

3

Hmmm, light BG in photoshop and I get the same thing:


Here’s the blend file, well, the relevant parts at least:
spark_Transparency.blend (4.92 MB)

4

what kind of format are you using to save the image?
Just because the brightness of your sparkles is way above what most image formats can deal with.
check this out.

5

Ahhh yes!

Saving the image as openEXR gives me a nice transparent image that works when overlaid over whatever colour.

Cheers!

6

So the next step is (and I know this probably isn’t a Blender question) , how would I convert an openEXR sequence into a nice portable avi or png sequence, as most spark and fire effects would usually be supplied?