Got Luts?

bsloan <bsl...@...>

I've used 10bit DPX for this purpose in the past (when I thought I'd
invented 2D 3D LUTs).

8 or 16 bit PPM may be a good compromise. It won't please everyone but
implementation requires so little code -- and the advantage of *not*
having to depend on openimageio may outweigh the disadvantage of
whining developers :).

There's some precedent for this -- NVidia's early Cg SDK provided the
source for a lightweight PPM IO library.

Who knows? This may be one case where OCS can influence the standard.


On Jun 8, 11:28 am, Larry Gritz <l....@...> wrote:
I wouldn't burden OCS with the image-reading functionality.  You'll never make everybody happy without supporting a bzillion formats.  Why not just allow the lut to be specified as a big array and call it a day, and let apps that use OCS be responsible for reading the image files (or having its own dependency on an image-reading library) in order to pass the array?

On Jun 8, 2010, at 11:10 AM, Naty Hoffman wrote:

There are some subtleties with layout and mappings, so let me know  
when it's time to implement the import/export logic and I'll write up  
a spec.
As for file formats, people use different ones - TIFF and TGA are  
common.  There are enough tools to support converting between 2D  
formats that I don't know if it's worth adding complex library  
dependencies to Open Color Space just for this. Does OCS have any 2D  
image file formats supported at the moment? PPM (the RGB version of  
PBM) could perhaps work - how widely is it supported by common image  
viewing utilities, OS thumbnails, etc.?
Sent from my iPhone
On Jun 8, 2010, at 10:05 AM, Jeremy Selan <jeremy...@...>  
Yah, the "lut as image" approach should be really easy to support,
I'll add that to the short list.  My only concern would be which
fileformats to support.  I'd still like to keep our dependencies as
low as possible though.  Naty, when folks use this approach in
production, which file formats are actually used to store the pixel
If it were a trivial ascii format (such as pbm,pnm, etc) that would be
ideal... ;)
-- Jeremy
On Jun 7, 7:04 pm, "Nathaniel Hoffman" <n....@...> wrote:
The 2D LUT format I describe below is starting to become a bit more
standardized in the game industry - it is being used by two major
middleware companies (Crytek and Epic - see here:http:// So it might make sense
to support it after all...
There are two LUT formats I know of that are used in game  
One is a 2D image format (any lossless image format will do -  
we've used
BMP, TGA and PNG) with a 2D representation of the LUT where the  
along the 3rd axis have been placed next to each other. So a  
32x32x32 LUT
would turn into a 1024x32 2D image. A common usage is for an  
identity LUT
in this format to be placed next to an ungraded screenshot, both
manipulated in Photoshop or some other color manipulation package,  
then the colorized LUT is extracted.
The other format is a DDS (Microsoft DirectDraw Surface) file with  
a 3D
texture in it, typically uncompressed. This is usually loaded  
into the game engine.
These are both a bit ad-hoc and not really standardized, so I  
don't know
if they are relevant for OCS. If they are, let me know and I can  
try to
work up something more like an actual spec for each of these.
I'm at the stage where I would like to get a survey of lut file
formats (1d, 3d, matrix, etc) that folks actually use in the wild.
If you commonly use a lut format at your facility, or define one in
your software package, I would hugely appreciate it if you could
upload example files and/or spec documents so I can begin work on  
Even if it's a proprietary format, I'd love to take a peek so I can
get a sense of the scope of formats out in the wild.  (I need to  
sure the internal API is rich enough to encompass current use  
Many formats have been mentioned previously, including:
   - Truelight ASCII .cub 3D lut
   - Assimilate Scratch  (Arri /Kodak .3dl)
   - Iridas Framecycler  (Iridas .cube)
   - Autodesk            (MESH3D, .lut, etc.)
For the majority of these, I do not have either example files or
specifications. Please help! :)
Also, does anyone know if the majority of lut formats  
identifiable by
their extension?  Are there common extension conflicts?  Ideally,  
like to try and have format reader registered based on file  
and only if that fails give each lut loader a chance to read it.
(Similar to how reader plugins work in nuke).
(Note that I'm not assuming 1 file == 1 lut.  (We will support  
where 1 file can generate multiple transforms, such as a 1d  
shaper lut
-> 3d lut -> 1d shaper lut.))
Larry Gritz