Blackmagic Forum

Hi,
I would like to inform about a bug in Resolve 15/Fusion TAB/Color Correction node
When colour correction is applied to a merged and scaled image the brightness, contrast and lift values seems to affect also the background.
It also happens with a DVE node
Other parameters are fine and if the merge node has a mask it also works as expected.
This is the FX with no colour node

Gain and colour transformation not affecting the background

Contrast, Lift and Brightness affecting the background


Is this a bug?
Many thanks
Albano

In a premultiplied image (one where you have transparent black pixels), changing the black point with Lift, Brightness, and Contrast affects those black pixels as well. They're not simply null.

In order to get the results you expect, you must first divide by the alpha, perform your correction, then multiply by Alpha again to knock those transparent pixels back down to black. There's a switch in the CC node (and other color correction tools like Brightness Contrast and Color Curves) labeled "Pre-divide/Post-Multiply" that will do this for you automatically, or you can bracket your color correction tools with an AlphaDivide and AlphaMultiply node.

Thanks Bryant,
I didn't know that.