2017

In order for the characterization to remain valid, a device must be calibrated. Calibration involves adjusting
the device to meet the "aim" (that is, the intended primaries, white point, and gamma) corresponding to
that characterization. This process must be repeated periodically because devices' responses drift with use
over time. For more information, see
Calibrating Your Monitor (page 1312).
Color Management Workflow
Color management involves converting color values between color spaces. This conversion happens at
specific points along a color pipeline.
■ When importing media, color values must be converted to a common working space so that color
information can be properly combined with other sources. For example, to combine on-set footage with
3D CG rendered elements and a painted matte background, the images should be in the same color space.
If the images originated in different color spaces, they require different input transforms to convert them
to a common working space.
■ While working, color values in your current working space must be converted to a color space that is
appropriate for your system's monitor. For example, if you are working in a scene-linear color space, then
you need to apply a transform that tone-maps the images and converts them to values that are appropriate
for your display. This display transform is not baked into the underlying color values, but is only applied
on-the-fly for previewing.
■ Also while working, you may want to switch color spaces to perform specific operations. For example,
some operations like compositing and blurring work best in a scene-linear space, but other operations
like noise and grain operations, or tracking and stabilization, work best in a video or log space. When
performing conversions like these, it's best to use an invertible transform to preserve the original color
information. In addition, you need to change your display transform to match the new working space.
■ Finally when outputting, you need to convert colors from your working space to the color space that is
appropriate for your deliverables. For example, SD video, HD video, and digital cinema all use different
color spaces, and require different output transforms.
Converting Between Color Spaces Using Connection Spaces
It is often necessary to convert between color spaces several times along an image pipeline. For example,
you may need to convert several inputs from different spaces to a common working space so that they can
be composited and blended, and then convert to another space for output.
To minimize the number of different color transforms that are needed to convert from each color space to
every other one, it is common to use one color space as an intermediate or connection space.
1304 | Chapter 25 Colour Management