Gamma Slamming

Gamma Slamming

Maybe you’ve seen an old movie on television—the example
I think of fi rst is Return of the Jedi (before the digital
re-release)—in which you see black rectangular garbage
mattes dancing around the Emperor’s head, inside the
cloak, that you obviously shouldn’t be seeing. Jedi was made
prior to the digital age, and some of the optical composites
worked fi ne on fi lm, but when they went to video, subtleties
in the black levels that weren’t previously evident suddenly
became glaringly obvious.
Don’t let this happen to you! Now that you know how to
match levels, put them to the test by slamming the gamma
of the image. The simplest way to do this is just to adjust
the Exposure control at the lower right of the Viewer up
or down. You can also make an adjustment layer, set it as a

guide layer so that it cannot render, and add a Curves or
Levels effect to push gamma up or down (different than
exposure—you may prefer it).
Slamming  exposes areas of the image that
might have been too dark to distinguish on your monitor; if
the blacks still match with the gamma slammed up, you’re
in good shape. Similarly, slamming up will give you a clear
glimpse of grain matching (and slamming the alpha, even
more so). Slamming down can reveal whether highlight levels
match; it’s particularly useful if you’re working in linear
HDR with over-range values

This is a useful habit anywhere that there is a danger of
subtle discrepancies of contrast; you can use it to examine
a color key, as you’ll learn in the next chapter, or a more
extreme change of scene lighting. Every big effects studio
I’ve worked at examines footage this way before it’s sent
for fi nal.