Blend Colors Using 1.0 Gamma

Blend Colors Using 1.0 Gamma

After Effects CS4 contains a fantastic option to linearize
image data only when performing blending operations:
the Blend Colors Using 1.0 Gamma toggle in Project Settings.
This allows you to take advantage of linear blending,
which makes Add and Multiply blending modes actually
work properly, even in 8 bpc or 16 bpc modes.
The difference is quite simple. A linearized working space
does all image processing in gamma 1.0, as follows
footage --> to linear PWS ->
Layer ->
Mask -> Effects -> Transform ->
Blend With Comp ->
Comp -> from linear PWS to OM space ->
output
whereas linearized blending performs only the blending
step, where the image is combined with the composition,
in gamma 1.0
footage --> to PWS ->
Layer ->
Mask -> Effects -> Transform -> to linear PWS ->
Blend With Comp -> to PWS ->
Comp -> from PWS to OM space ->
output
(Special thanks to Dan Wilk at Adobe for detailing this out.)
Because effects aren’t added in linear color, blurs no
longer interact correctly with overbrights (although they
do composite more nicely), and you don’t get the subtle
benefi ts to Transform operations; After Effects’ much
maligned scaling operations are much improved in linear
fl oating point. Also, 3D lights behave more like actual
lights in a fully linearized working space.
I prefer the linear blending option when in lower bit
depths and there is no need to manage over-range values;
it gives me the huge benefi t of more elegant compositesand blending modes without forcing me to think about
managing effects in linear color. Certain key effects, in particular
Exposure, helpfully operate in linear gamma mode.

Output

Finally, what good is it working in linear fl oating point if
the output bears no resemblance to what you see in the
composition viewer? Just because you work in 32-bit fl oating
point color does not mean you have to render your
images that way.
Keeping in mind that each working space can be linear or
not, if you work in a linearized color space and then render
to a format that is typically gamma encoded (as most
are), the gamma-encoded version of the working space will
also be used. After Effects spells this out for you explicitly
in the Description section of the Color Management tab.
To this day, the standard method to pass around footage
with over-range values, particularly if it is being sent for
fi lm-out, is to use 10-bit log-encoded Cineon/DPX. This is
also converted for you from 32 bpc linear, but be sure to
choose the Working Space as the output profi le and that in
Cineon Settings, you use the Standard preset.
The great thing about Cineon/DPX with a standard 10-bit
profi le is that it is a universal standard. Facilities around
the world know what to do with it even if they’ve never
encountered a fi le with an embedded color profi le. As was
detailed earlier in the chapter, it is capable of taking full
advantage of the dynamic range of fi lm, which is to this day
the most dynamic display medium widely available.

Conclusion

This chapter concludes Section II, which focused on the
most fundamental techniques of effects compositing. In
the next and fi nal section, you’ll apply those techniques.
You’ll also learn about the importance of observation, as
well as some specialized tips and tricks for specifi c effects
compositing situations that re-create particular environments,
settings, conditions, and natural phenomena.