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Subject: Re: [AE] Inverse a LUT?
From: Brendan Bolles <brendan@fnordware.com>
In-Reply-To: <list-4614805@media-motion.tv>
Date: Thu, 2 Feb 2012 12:13:56 -0800
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References: <list-4614805@media-motion.tv>
To: "After Effects Mail List" <AE-List@media-motion.tv>

It depends on your LUT.  If it's a 3D LUT, then it can not be inverted =
in general. 1D LUTs can often be inverted.  LUT Buddy has an invert =
button that will be enabled when the LUT is invertible.

In the 3D LUT case, imagine you had a LUT that was used to turn your =
image black and white (desaturate).  As you know, no color operation =
could hope to magically restore the color once it had been taken out.  =
So that's a clue as to why 3D LUTs can't generally be inverted.

If you created your 3D LUT using a series color corrections, your best =
hope is to try to apply them in reverse with inverted settings.  You =
could then make a LUT of that operation to be your inverted LUT.

But usually you just try to come up with something close or deal with it =
on a case-by-case basis.


Brendan


On Feb 2, 2012, at 11:09 AM, Byron Nash wrote:

> I was wondering if there is a way to inverse a LUT? I'm applying an =
Arri Alexa LUT to some footage for VFX work. Some of the elements are =
graphics that need to maintain their color with and without the LUT. We =
have been using a LUT on an adjustment layer and then turning it off =
before rendering it. That way our VFX should be in the correct ranges =
for Color Correction. This works fine for source footage but as soon as =
you need to put a logo in there it gets weird. I'd like to be able to =
put a reverse of the LUT on the logo/graphics and keep all that under =
the Adjustment layer.  In the past we have just sort of used levels and =
curves to approximate the graphics with some success. But I'd like to do =
it the "right" way.=20