ChromaAb + ChromaMerge Toolset
A streamlined chromatic aberration solution designed for high-end integration. While most similar tools only distort RGB information, this solution treats the alpha channel the same way, preventing 'chopped' edges during the final merge.
Minimum knobs, maximum control: Every parameter is carefully selected to offer advanced features without a bloated interface.
ChromaAb Knobs:
Channels: rgba/alpha (RGBA is default, for alpha, see explanation below.)
red/green/blueAb: The amount of aberration on logarithmic sliders (x/y can be set separately).
red/green/blueBlur: Self explanatory. Aberration edges can be softened (x/y serparately).
ControlMatte: Controls the amount of chromatic aberration, just like any other matte would do.
viewControlMatte: Switch this on to set up the matte.
matteCenter/Scale/Softness/Blur: With the viewControlMatte switched on these should be self-explanatory.
ChromaMerge Knobs:
Operation: over/under. For non-alpha operations, standard Merge node should be used instead.
Set bbox to: Self explanatory.
Premultiplied: Enable if the primary input (A for over, B for under) is premultiplied.
Why use this over other tools?
- The rgbAlpha Layer: This is the key to proper integration. Most tools distort the alpha as a single channel, which "chops off" the edges where RGB channels have drifted apart. ChromaAb generates a hidden rgbAlpha layer (an RGB-split version of your alpha) that ChromaMerge uses to reconstruct a technically correct edge during the merge.
- The "Alpha-only" Feature: Perfect for matching a roto or a mask to a plate that already has aberration (like a film scan). By aberrating only the alpha channel, you can align your mask perfectly to the existing plate's aberration.
"I hate your tools, I have my own favourite CustomChromaticAberration"
Fine. Good news is: you might not even need them at all. Let's check:
- Will you do any alpha merging with your aberrated element? No? Then feel free to use whatever tool you like for the aberration, and a standard Merge node for the final operation (plus, screen, etc.).
- Is your aberration very subtle? Yes? You might get away with a satndard Merge node (though technically it’ll be incorrect, but hey, if the client doesn't see it...).
- Still here? That means you've got those ugly chopped-off edges. Don't worry, you still don't have to use my ChromaAb node. With a few extra steps, you can properly merge your own custom aberration:
Using ChromaMerge with any custom node:
If you have a favorite aberration tool, you can still use ChromaMerge for a clean result:
1. Duplicate your custom aberration node.
2. Take your input’s alpha channel, shuffle it into all three RGB channels, and feed it into the duplicated aberration node.
3. Shuffle this newly created three-colored alpha into a layer called "rgbAlpha".
4. Copy this layer back into your original RGBA stream.
5. Now you can use ChromaMerge to properly merge your element without losing those edge details.
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