2017

First, you must ensure that the images are scene-linear:
■ Output-referred images, such as video and sRGB, should have the gamma removed and an inverse tone
map applied. These two operations are often combined in one transform. Ideally, you should use the
inverse of the tone map that will be used for output and display. For example, if you will be using the
ACES RRT tone map, then you can use sRGB_to_ACES from the RRT+ODT/ directory as an inverse tone
map. Alternatively, inversePhotoMap_gamma_2.4 from the primaries/ directory is a generic transform
that works well in many cases.
NOTE Although it is common to simply remove the gamma from output-referred images, this is not enough
to convert images to scene-linear — an inverse tone map is always required. However if a digital photograph
was not flatly lit, or if a digital painting uses overly bright colors, then an inverse tone map may create values
greater than 1.0. In these cases, the best approach may be to use one of the remove_gamma transforms in
the gamma/ directory without applying an inverse tone map, even though this is not ideal.
■ Log-encoded images should have the log encoding removed using one of the transforms in the film/
directory. See
Color Managing Images from Scanned Film (page 1314) for additional considerations.
■ Scene-linear images, such as images prepared using a tone map for display, can be used as-is if the primaries
match your working space.
Once the images are scene-linear, you can convert the primaries to your working space using one or more
of the transforms in the primaries/ directory. For example, if you converted an image to scene-linear ACES
and you want to render using the UHDTV (Rec. 2020) primaries, you can apply ACES_to_CIE-XYZ followed
by CIE-XYZ_to_LinearUHDTV.
Light Sources
Maps that represent light sources should be scene-linear but can contain values greater than 1.0. These
include reflection maps, environment maps, and backplates, as well as some other effects such as
incandescence.
■ Output-referred images, such as video and sRGB, should have the gamma removed and an inverse tone
map applied. After that, you can convert the primaries if necessary.
■ Log images should have the log encoding removed, and then the primaries converted if necessary.
■ Scene-linear images only need to have the primaries converted if they don't match your working space.
Non-color Data
If images are used to control non-color attributes, such as normals, depth, and so on, then the values should
not have any color transform applied.
Color Management and Image-based Lighting (IBL)
The algorithms used to render 3D CG graphics require scene-linear colors, and images intended for
image-based lighting are typically supplied as HDR or OpenEXR images that are scene-linear already. However,
the images might still require some color management.
If the primaries used to encode an image do not match the working space used for rendering, then the image
should be converted using one or more of the transforms in the primaries/ directory. For example, if the
image uses the Adobe RGB primaries and you want to render using the UHDTV (Rec. 2020) primaries, then
you can apply LinearAdobeRGB_to_CIE-XYZ followed by CIE-XYZ_to_LinearUHDTV.
Autodesk Color Management | 1317