Problem compositing glow on multiple layers

Support Compositing and Post Processing
#1

I’m trying to composite 2 layers with different colours, each with a glow effect. Unfortunately, when I combine them it produces a render that is way too bright and drowns out the colours of each layer. I’ve tried add, mix, screen and alpha over, as well as Filmic Blender (to increase dynamic range) and CDL node, but nothing seems to work. How can I composite these while preserving their colours? Is it possible to have layers that don’t affect each other’s brightness/contrast?

Here’s the first layer:

UV1UK.jpg1342×762 248 KB

Here’s the second:

VdMK6.jpg1363×811 301 KB

This is what happens when they’re combined:

fyC8j.jpg1343×767 91.2 KB

#2

You will have to adjust the colors in the RGB curves. Adjust the settings until you can see the colors that you see. Tweak the actual curves on the Red, Green, and Blue Color curves.

#3

I’ve tried that, however it changes the colour of the glow but the inner parts are still bright white.

#4

Have you tried changing the mix nodes?

#5

Yes I’ve adjusted the mix shader for the yellow layer, as well as adding an alpha over node instead of add at the end. Here’s a screenshot of my latest tweakings. Still not looking right though;

screenshot 1.jpg1893×877 417 KB

#6

Is there some sort of source of inspiration, like a image that your trying to achieve?

#7

Yes, basically like this:

screenshot 3.jpg1000×853 152 KB

#8

Proper glows can only be accomplished in a single pass with associated alpha. They are essentially an add. If you save to a junk format such as PNG, the resultant alpha / RGB values lose their emissive structure. Save to an OpenEXR and composite accordingly.

The dynamic range of your view transform also matters, as it will be the ceiling of the resultant scene referred ratios. The sRGB OETF / EOTF doesn’t provide enough room to properly composite glows, flares, blooms, etc. and will yield display referred white with almost a trivial level of intensity.

#9

A bright yellow and bright blue produce white. To get both yellow and blue in different parts, you should give different elements more “room” so that they don’t sit exactly on top of each other.

The Ghostbusters reference is a good example, the blue twirls are around the orange whips, not directly on top of them, so they are both clearly visible.

#10

Didn’t realize the file format really mattered in emission…good to know! I’ve been playing around with the Filmic add on and yes, it definitely has improved the dynamic range.

#11

This is very true! I didn’t realize the over exposure was so apparent because the 2 colours were overlapping so much. You can see where even in the Ghostbusters pic it happens in some spots. When I finish tweaking the blues, I’ll post it for others to refer to.

#12

Also, if you take a close look at these two movie stills, which were (necessarily) composited using film techniques, you will see that the various layers overlay one another: they don’t combine at all. Also, each element is visually distinct from the rest.

So, in the shot in post #1, what I would do is to separately develop at least three separate things:

(1) “A pudgy glow.” Pick your color, but pick one color. Even if the glow is derived from something else, you want just the glow.

(2) The fat yellow beam from the first shot, but without the glow.

(3) The prickly blue beam from the second, also without the glow.

Composite the shot by laying each overlay on top in the order given. Adjust alpha on the final result and lay it on top of the scene.

Each composite layer is visually distinct, self-contained, and different.

#13

Honestly, it will work just fine. Just use a decent dynamic range and either:

  • Properly generated associated alpha glows
  • Properly added glows

It will work just fine. Have faith. :wink: