Primary Color Correction: Tonal Correction Tools - The Art and Technique of Digital Color Correction - page 50

Forms and Functions of Histograms

In some programs, the histogram is not limited to displaying the master
histogram. For example, in many applications, you can also display histo-
grams of the Composite level (saturation and luminance together), Luma,
and individual levels for each of the red, green, and blue channels.

… the danger signs of a histogram: sharp peaks or “cliffs” at either
end …

These individual histograms can be useful for spotting problems with the
individual channels. As I mentioned in the sidebar, sharp spikes at either
end of the histogram indicate clipping (lots of pixels jammed into the same
tight tonal range). You can look at the individual color channels' histograms
and see whether a specific color channel is more clipped than another, or
if there is an entire tonal range that is weak in a certain color channel. I've
actually seen footage from cameras with severe technical problems where
there was absolutely no information in a particular color channel.
The trick with Symphony's Levels controls is that there are both input
and output Level controls. These are tied together. The input controls
seem counterintuitive; as you move the shadow triangle to the left, the
level of blacks goes up, and moving it to the right makes black levels go
down. The reason for this is that when you move the black level to the
right on the input side, you are telling Symphony to map all of the levels
to the left of the triangle to a lower level.
However, if you move the same black triangle on the output side to the
right, you are telling Symphony that all of the levels of black that are at or to
the left of the input black triangle should now be mapped to a higher level.
A way to understand this is to look at the curve in between the two
histograms as you move the input, then the output black triangle. On the
input side, moving the black triangle to the left or right moves the black
point on the curve go left or right. But moving the black curve on the
output side moves the black point on the curve up and down.
To best study how this works and get it “under your fingers” is to
call up a black-to-white ramp or chip chart and simply slide the faders
around, watching the waveform carefully as well as looking at the result
on the video monitor.

D e f i n i t i o n
under your fingers:
This is a term that musi-
cians use to describe
practicing something
enough times that the
movements become second
nature. Basically, it means
developing muscle memory,
in which your body knows
what to do without your
brain consciously thinking
about it.

Curves Tab

Curves in Apple's Color, Avid, Resolve, and Synthetic Aperture's Color
Finesse are similar to the Curves controls of several other products, like
Adobe's After Effects and Photoshop. They allow pinpoint control over