From: "Chris Zwar" <chris@chriszwar.com>
To: "After Effects Mail List" <AE-List@media-motion.tv>
Importance: Normal
Sensitivity: Normal
Message-ID: <W369924258315501328237300@webmail105>
Date: Fri, 03 Feb 2012 02:48:20 +0000
Subject: Re:  [AE] Inverse a LUT?
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

I'm working with Alexa footage at the moment, but I wasn't 100% sure by w=
hat you meant by 'inverse'.  But I think I've got it now.  Basically you'=
ve downloaded a LUT to convert the Arri LogC format into a rec709 colours=
pace to work with in AE.  Now you need to convert your renders back to th=
e original Arri LogC colourspace?
If that's it then I don't know how you can do it inside After Effects.  T=
he Arri LUT converter only creates LUTs that go one way.
Can you export a different format - can you use the Cineon converter to p=
rovide Cineon Log files instead of Arri Log files?
Not sure if other software such as Nuke can do this, you might have to re=
nder out 32bit dpx or exr and have them converted back to Arri LogC in a =
different package.

-Chris

-----Original Message-----
From: Byron Nash [mailto:byronnash@gmail.com]
Sent: Friday, February 3, 2012 01:25 PM
To: 'After Effects Mail List'
Subject: Re: [AE] Inverse a LUT?

That's what I'm doing, and it works great until you have to put a piece o=
f
footage or a graphic in there that has a different color space. What we a=
re
trying to do is deliver a shot to color correction that does not have the=

LUT applied.

On Thu, Feb 2, 2012 at 8:52 PM, Chris Biggs <christopher.biggs@gmail.com>=
wrote:

> I  apply my LUTs to an Adjustment layer on top of my comp, then make it=
 a
> guild layer, as to not render out
> no need to reverse then.
>
>
> On Thu, Feb 2, 2012 at 12:51 PM, Byron Nash <byronnash@gmail.com> wrote=
:
>
>> It's a 3D LUT from the Arri site, LogC2Video_Rec709.
>>
>>
>>
>> On Thu, Feb 2, 2012 at 3:13 PM, Brendan Bolles <brendan@fnordware.com>=
wrote:
>>
>>> It depends on your LUT.  If it's a 3D LUT, then it can not be inverte=
d
>>> in general. 1D LUTs can often be inverted.  LUT Buddy has an invert b=
utton
>>> 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 t=
hat'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 bes=
t
>>> 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 Co=
lor
>>> Correction. This works fine for source footage but as soon as you nee=
d to
>>> put a logo in there it gets weird. I'd like to be able to put a rever=
se of
>>> the LUT on the logo/graphics and keep all that under the Adjustment l=
ayer.
>>>  In the past we have just sort of used levels and curves to approxima=
te the
>>> graphics with some success. But I'd like to do it the "right" way.
>>>
>>>
>>> +---End of message---+
>>> To unsubscribe send any message to <ae-list-off@media-motion.tv>
>>>
>>
>>
>
>
> --
> ---------------------------------------
> R.Christopher Biggs
> Digital Ronin
>