Understanding ColorCorrection node behavior

Hey there...

Lets say:
- I have two clips in Fusion merged
- i mask out a part of the fg clip with a rectangle for example
- i throw in a cc node in the masked fg clip pipeline

When i then play with the gamma in the cc-node, it behaves like i want it to. It changes the gamma of the fg clip only.
But if i play with the brightness or contrast sliders for example, it changes the whole output (including the bg clip)

I want to know why it`s like that and if there is a work around...

Any hints?

Cheers

Thomas

You need to check the 'pre-divide/post multiply' checkbox in the color correction node (I think that's what it's called) in one of the tabs. That should solve your problem.

You need to use the Pre/Post multiply checkbox on the CC node.
When you adjust things like brightness, this can introduce negative values for example. Or push values up, even if the alpha is 0.
Gamma will keep lower and upper values untouched which is why you don't see that reflected in the merged image.
It's generally a good idea to use the Post multiply checkbox to avoid edges with possibly problematic luminance.
You could also divide the alpha prior to the CC, then multiply it again after the CC and have the same effect.

This post by Bryan touches this topic as well:
http://www.bryanray.name/wordpress/blac ... he-basics/

If you're a beginner you should definitely check out his posts.

While I'm not a Fusion beginner anymore, not a day passes in which I don't mourn the fact that he isn't writing on his Fusion book anymore. I can't imagine how much valuable information he still has to offer.
(He still offers incredible amounts of information here and on WSL, but a complete composting handbook by him would still be incredible)

You need to check the 'pre-divide/post multiply' checkbox in the color correction node (I think that's what it's called) in one of the tabs. That should solve your problem.

Yeah, problem solved. Thanks a lot...still dont understand why negative numbers can apear, but as long as i understand the issue and have a workaround, i wont dive into math madness

While I'm not a Fusion beginner anymore, not a day passes in which I don't mourn the fact that he isn't writing on his Fusion book anymore. I can't imagine how much valuable information he still has to offer.
(He still offers incredible amounts of information here and on WSL, but a complete composting handbook by him would still be incredible)

Great site/blog. Never came across yet.
Guess the development is too fast to keep everything so detailed and in depth and its just too much time for someone who does not get paid for...

He should really be on the payroll.

No thank you. I'd rather be out here in the world learning and growing (and adding to my IMDb page) than doing technical writing for a living!

Now that the icon set is mostly complete, and the UI might be settling down a bit, I'm hoping to start back in on the second draft. And to finally get the first draft of that automation chapter written.