Adobe 65008009 - After Effects CS4 Technical Paper page 27

cases, this option should remain checked to enable correct viewing and rendering of composi-
tions. For more information on this feature, see the white paper discussing this issue on the
Adobe web site at www.adobe.com/go/learn_ae_sceneoutputreferredpaper.
The list of Adobe-supplied profiles at the beginning of this appendix provides information defin-
ing profiles as either "scene" or "presentation environment" type profiles.
limited-range video profiles (hdTv (rec. 709) 16-235, SdTv nTSC 16-235,
and SdTv PAl 16-235)
If you have already looked at the profile lists in After Effects CS4,
you may have noticed several color profiles with names ending with
"16-235". You may be wondering what these profiles define and when
they would be used in your workflow.
These profiles are built to support video workflows that require the
user to define a limited tone range for the RGB values used in the
After Effects project. Why would this be necessary? In many cases,
recorded analog video limits the range of tone in a captured image
to "video safe" levels of luminance (normally IRE values from 7.5 to
100 in the US). However, it may be the case that luminance levels are
recorded below 7.5 IRE (super black) or above 100 IRE level (super
white or overbright). This presents a problem. When these analog
IRE voltage values are translated to the YCbCr color space during
the analog to digital conversion, it is normal for the 100 IRE value to
translate to 235 Y (the luma part of the YCbCr color space) and the 7.5
IRE value to translate to 16 Y. Since After Effects works with RGB val-
ues, there will be an additional translation from YCbCr to RGB before work can be done in After
Effects. The translation of colors from YCbCr to RGB is normally done by the codec used for a
specific video format. This codec may translate the luma values to limited range RGB (16-235) or
the codec may translate luma values to full range RGB (0-255). In some cases, a codec used in the
workflow may have controls for how it will interpret luma values. In other cases, this translation
is hidden from the user. You may be working with footage from several different formats that
treat luma levels in different ways. This could add additional time and cost to your project as you
manually tweak each piece of footage to comply with the requirements of your output.
The Adobe-supplied "16-235" profiles address this issue and provide additional flexibility in
workflows where control of luma expansion/compression is critical. Here are some workflows
where the use of the "16-235" profile may be helpful:
1 Expand luma levels on import:
If your HD (or SD) footage has limited range of 16-235 and you would like to expand values
in your footage to the full RGB range of 0-255, choose a full range RGB profile in the Working
Space menu in the Project Settings dialog box (probably the HDTV (Rec. 709) profile) and
assign the HDTV (Rec. 709) 16-235 profile to your footage in the Interpret Footage dialog box.
After Effects will convert colors from the profile you assign in the
Interpret Footage dialog box to the project working space profile,
mapping 16 to 0 and 235 to 255 when the colors are converted.
Choosing the "16-235" profiles in Interpret Footage dialog box
and using a non-"16-235" profile as your working space will
achieve the same result as choosing the Expand ITU-R 601 Luma
Levels option in the Interpret Footage dialog box in After Effects
7.
Note: When working in 8-bpc or 16-bpc mode, colors from 0-16
and 235-255 will be clipped.
2 Maintain luma levels in project at 16-235:
If you would like to maintain the 16-235 range in your project
and view RGB 16 as darkest black and RGB 235 as maximum white
on your computer monitor, choose the HDTV (Rec. 709) 16-235
profile in the Working Space menu in the Project Settings dialog
Y=255
overbrights
100
Y=235
7.5 Y=16
super black
0
Analog
IRE
Figure 1 — Luma expansion to full-range RGB
Y=255
overbrights
Y=235
Y=16
super black
Y=0
YCbCr
Figure 2 — Maintaining luma levels in the After Effects project
overbrights
super black
Y=0
YCbCr
(After Effects
RGB=255 Y=255
overbrights
RGB=235 Y=235
RGB=16 Y=16
super black
RGB=0 Y=0
RGB
(After Effects
project)
Color management workflow in Adobe After Effects CS4
RGB=255
RGB=0
RGB
project)
overbrights
super black
YCbCr
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