Hello Folks,
I had to replace the background in a shot and had problems with a red area in the semi-transparent ones, which I found difficult to get out.
I then tried to filter out the red using the RGB channels and it worked fantastically. Unfortunately I have no idea what this method is called. Maybe someone has a few tips and tricks.
Thanks!
Here is the setup:
Here the before and after:
Nice solution. You can call it channel separation. Also you can use the Separate node which has 3 output tabs. It can sparate RGB as well as YUV and HLS which comes handy sometimes. The Combine node you used can be used for YUV/HLS too.
What are you doing in the cooler correct node? De-Sat?
Yes Channel séparation IS very usefull !
I’ve seen in the past a similar tips but forgot how to do it. It allowed to only change the luminance of the image whitout affecting the color, in case of someone know and can explain 
@eversondigital
there I turned the green channel in the direction of the red channel via the gain
You can also do that in the MasterGrade Matchbox, under curves, H-H curve allows you to rotate specific hue ranges. You have curves of H-H, H-L, H-S, correcting hue, saturation, and luminance for a specific hue range.
You do get a nice fall-off on the range. You can add control points to narrow the range.
There are corner cases where it has a hard time isolating a hue, and you have to fall back to other methiods. But 90% of the time that’s an easy way to swing colors.
And if you need help finding the hue in a complex image, set the eye dropper on your problem area, and the H-H curve will show a vertical line where that hue is. Then you can either add a point on the curve (A + click), or move one horizontally into place:
Joel Osis once showed a trick of sharpening just the red channel to limit that icky black edge fringing when sharpening and it can be a nice trick in a pinch. Throwing it out there as well!
