Blackmagic Forum

Hi,

I've looked for this answer on youtube but almost every video out there only talks about outputting alpha channel out of Resolve or how to add a title with a transparent background.

What I am looking for is how to ADD alpha channel to my video clip. Here is the use case; I rendered a fractal animation (500 frames which I converted to .MOV). There is some black background visible in the clip and I'd like to make it transparent for use in another app.

How can that be done? I'd assume Fusion may need to be utilized, if so what is the best way to do this?

thanks
jake

Hello,
The best way would be to output the seminal animation with alpha layer, its the normal way to do it.
For example, I made animation with Houdini or TouchDesigner, I output to .exr or .png sequence or .mov with animation RGBA codec. So th alpha mask is embeded.
If your background is black, you can try to use luma keyer in Fusion page to add an alpha mask for the black. But it depend of the other part of the image. If there is another black in it…
You can also use the color page:
– qualifier to isolate the black
– power window as garbage mask and concentrate on the subject
– tracking to follow the subject
– inverse Node
– add a alpha output
– wire the last node alpha to the alpha output
When you go back to edit page, your clip have alpha layer

Unfortunately I did not output my frames with alpha channel, hence the need to do it after they've been assembled. The final output will be used in Resolume (since you've mentioned TouchDesigner!). So in order to layer animations having alpha channel present is the preferred method for Resolume use.

Which one of these options would be most effective (Fusion vs Color page)? I actually have few hundred of these animations so from a workflow perspective I'm looking for a quick/easy way to add the alpha channel since it will have to be repeated multiple times.

thanks
jake

Jake Melon wrote:I actually have few hundred of these animations so from a workflow perspective I'm looking for a quick/easy way to add the alpha channel since it will have to be repeated multiple times.

I'm afraid to be the bearer of bad news, but even the "quickest" and "easiest" ways are going to be an awful lot of time and drudgery if you're talking about hundreds of clips.

If there's something unique about the background that isn't any part of the foreground such as luminance or colour, then a chroma or luminance key in Fusion would probably be the easiest way to do it. But even that usually requires close review and cleanup to make it work well.

The animations came from somewhere - considering the task you're facing I'd suggest it would be worth investigating whether or not they can be redone.

Hmm, some of these fractal animations took over a week to render so re-rendering is not an option.

jake

Jake Melon wrote:Hmm, some of these fractal animations took over a week to render so re-rendering is not an option.

Well, if nothing else you now know to make sure that any future animations are rendered with an alpha channel in order to save you time on your future projects.

Sean Nelson wrote:

Jake Melon wrote:Hmm, some of these fractal animations took over a week to render so re-rendering is not an option.

Well, if nothing else you now know to make sure that any future animations are rendered with an alpha channel in order to save you time on your future projects.

Can you post a single frame?

It is possible to use ffmpeg for automatically luma keying your footage and injecting alpha channel. Look at this Reddit thread for a handle: https://www.reddit.com/r/ffmpeg/comment ... _to_alpha/

You could scan through all your source clips in a batch process loop and autogenerate alpha for them.