TMI Color Temperature Correction

Screenshot of Nuke's TMI slidersOne of the things that I miss in Fusion whenever I have been using Nuke is a way to adjust colors using color temperature. Yes, there’s a white balance tool, but it’s a bit of a black box and it doesn’t have the kind of sliders known from Nuke (or even Photoshop’s RAW converter). I think Fusion’s tool is pretty accurate in terms of color science, but for eyeballing adjustments or creative tinting the other programs’ sliders are more useful.

Nuke provides the TMI system in its color picker so you can use it anywhere you see a color swatch. One parameter adjusts the color temperature by moving red and blue in different directions (you don’t have to specify a proper temperature like 5300K). The second parameter is a shift along the magenta/green axis.

Here’s a macro which allows you to tint an image using this system in Fusion. I don’t know if the formulas I’ve reverse-engineered are only used in Nuke or if there’s a standard for TMI (it’s kinda hard to find information about it). It goes without saying though that all of this is only valid in a linear color space. Reportedly it was also useful to cancel the effect of the ARRI Alexa’s white balance and CC Shift settings.

update August 2013:

I’m getting a bunch of Google hits for the TMI system, although I haven’t spelled out the formulas I’ve used for my macro. Here they are (as used by Nuke’s color picker)…

Color Temperature (T):

Red Gain = 1 – T/2, Blue Gain = 1 + T/2

Magenta/Green (M):

Red Gain = 1 + M/3, Green Gain = 1 – M*2/3, Blue Gain = 1 + M/3

Intensity (I):

RGB Gain = 1.0 + Intensity

Download the macro here or view the help page on vfxpedia.

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