For RED footage, you can determine these quite easily, because you have
the source and target images..
If you write out an image in the CameraRGB colorspace, and the exact
same frame in RedColor, you can ~randomly try values in a ColorMatrix
until they match
Manual steps would be:
* connect a ColorMatrix node to the CameraRGB image
* Compare the ColorMatrix node to the Redcolor image
* Adjust the first row of the matrix until they match...
Starting values for the first row would be 1, 0, 0 (which just creates
the red output channel by doing: red*1 + green*0 + blue*0)
Repeat the same for the other channels, and you have the node ot convert
from CameraRGB to RedColor (which can be inverted easily)
I've been meaning to do this for the various RED colorspaces, and wrote
a script to determine these automatically
https://github.com/dbr/colourstuff/blob/master/lib/python/colourstuff/determine_colour_matrix.py
..but never got around to finishing the script, running it on real
footage, and writing up the results (it would be useful to have a
freely-distributable, one-frame R3D file of a colour chart and something
with a lot of luminance range - all the footage I have access to to is
copyrighted or otherwise unusable for an opensource-type thing)
That said, I wanted to do this for a different reason: So we could be
sent converted RED footage with RedColor burned in, reverse it for doing
comp stuff, then reapply before sending to DI. Or it would allow working
with EXR's in CameraRGB, then applying the RedColor look later (e.g in a
viewer LUT)
To answer the original question...
> Doing the linearisation is easy. But how do I match the gamut?
Basically, I'd suggest just linearising the footage as best as you can,
and doing some grading by eye to match the colours. Using the gamut
remapping is nice in theory, but in reality it doesn't work too well in
my experience..
It'll work for CameraRGB<->Redcolor and such because they are
mathematically perfect linear-transforms done in the RED SDK.. Whereas
the differences between two cameras is squishy physical optoelectronic
stuff.
Thing I just remembered about: ACES. It might have transforms for the
ALEXA and RED cameras, which would do exactly what you want, if they are
available yet
On 24/01/13 19:04, Simon Björk wrote:
I've been talking to RED about this, but they are very secret with their
color operations. For example, I would like to be able to convert from
their own "CameraRGB" color-space to Redcolor as CameraRGB can give you
very clean keys. I have some charts shot, but I don't think that would
help much.
/Simon
2013/1/23 Schneider, Abraham <[email protected]
<mailto:[email protected]>>
Hi there!
I have an Alexa project where I have several plates that were shot
on RED. To mix these plates with Alexa footage, I'd like to
'convert' the RED footage to AlexaV3. Doing the linearisation is
easy. But how do I match the gamut? I know, it's more of a
theoretical thing, because I always have to colograde the files. But
how would I do this properly? To do this, I'd like to use the
Colorspace node, set the 'out' gamut to 'AlexaV3LogC'. But what do I
use as 'in' gamut?
Anyone knows, which primaries are used in REDcolor, REDcolor2 and
REDcolor3?
Thanks, Abraham
Abraham Schneider
Head of VFX pipeline / VFX Supervisor
ARRI Film & TV Services GmbH
Tuerkenstr. 89
D-80799 Muenchen / Germany
Phone +49 89 3809-1269 <tel:%2B49%2089%203809-1269>
EMail [email protected] <mailto:[email protected]>
www.arri.de/filmtv <http://www.arri.de/filmtv>
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Geschäftsführer: Franz Kraus, Dr. Martin Prillmann, Josef Reidinger
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