Photoshop User - USA (2020-02)

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Now let’s look at a gradient that’s
squished to one side. Instead of the midpoint
being exactly 50% gray, let’s move it toward
the shadows.
The bars are clearly no longer aligned,
but because we already have pure black and
white in the gradient, how do we even out
the distribution? The midpoint slider! This
important little fella is actually a gamma
correction slider. While the endpoint sliders
range in luminosity values from 0 to 255, the
gamma slider ranges from 0.01 to 9.99, but
the midpoint is 1.00 instead of 128. The rea-
son for this is because this slider isn’t specifi-
cally remapping a luminosity value so much
as controlling the midpoint (hence the name)
of the transition from black to white. So the
numeric value represents a relationship, not
an absolute value.
Note: If you’re interested—and I know at
least some of you are—the midpoint value
is the exponent in the following equation:
V out = V in ^ gamma. V is luminosity here, so
this reads: output luminosity is equal to the
input luminosity raised to the power of the
gamma value. This is why the middle value
is 1.00, meaning the input value is exactly
the same as the output value. Gamma is also
nonlinear, and if you’re interested in the math,
drop me a note on the KelbyOne Commu-
nity forums. For now, just realize that 1.00
means “dead center” and that when you
move either the shadows or highlights sliders,
the midpoint slider moves to maintain its rela-
tive position between those two sliders.
Moving the midpoint slider to the right
expands the shadows, while moving it to the
left expands the highlights. In this case, we
want to drag out the shadows, so we move
the midpoint to the right to offset the unbal-
anced gradient.
In this way, Levels lets us redistribute
the dynamic range with the gamma slider,
expand the dynamic range with the Input
sliders, and limit the dynamic range with the
Output sliders.

Corrected histogram

Gradient Editor

showing offset

of 50% gray to

the left

Gradient and Posterized bands offset

Corrected bands