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Of the several ways to adjust the tonality of
Photoshop images, applying an adjustment curve is
perhaps the most useful. Curves providing broad
changes, as shown below, or the more precise
corrections needed when making digital negatives,
can be created, saved, reloaded, and applied with
either the Adjust
Curves or Transfer
Functions tools. Curves made with one tool
may be loaded and applied from the other, the
Adjust Curves tool used to alter the image itself,
while the Transfer Functions tool serves to modify
the way the image is printed.
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Original image,
no adjustment
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Image lightened
with "Adjust Curves"
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Image darkened
with "Adjust Curves"
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The Adjust Curves tool provides 2
options for altering the shape of the
curve.
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The curve may be altered by "dragging"
the various points up or down. When
dragging a point on the curve, the
previous (Input) value and the current
(Output) value are displayed
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If the pencil icon is activated, the
curve may be drawn freehand and ...
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smoothed by successively clicking the
"Smooth" button. Notice that the Input and
Output display is deactivated.
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After smoothing the freehand curve,
clicking on the "graph" icon allows you to
return to "dragging" mode, where the
values of the various points can be
checked. Notice that the "Smooth" option
is no longer available.
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If the curve is saved, it may be
"loaded" with the Transfer Functions tool,
where individual values are displayed and
may be changed either by dragging the
curve, or entering numerical values.
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Each time the Adjust Curves tool is
activated, a straight line is initially displayed,
regardless of any previous alterations. UNLESS,
curves are applied to an "Adjustment Layer" (Layer
> New > Adjustment Layer > Curves). An
Adjustment Layer retains and displays the last
setting and permits repeated adjustment, or
deletion of the alterations, without damaging the
original image. An additional advantage of the
Adjustment Layer is that changes are seen as the
curve is being altered, and, for comparison, may be
temporarily "switched off", without loss, by
de-selecting the Adjustment Layer.
When printing from Photoshop to an Epson printer,
the Transfer Function is accessed through "Page
Setup". It is designed to alter the way the printer
deposits ink, and has no effect on the image itself
or the way it appears on the monitor. In my view, it is also the best way to
create or modify an adjustment curve, since
individual values can be set. Curves which have
been saved from either the Transfer Function or the
Adjust Curves function, can be opened and applied
from either. Since the "factory" settings for my
Epson Stylus Photo 1200 printer provided less than
ideal color and tonality for my taste, I
found it useful for adjusting the amount of ink
deposited in both color and B&W printing.
No indication of the presence of a Transfer
Function adjustment will be seen in the image
without accessing Page Setup>Transfer Function
and viewing the curve, so care must be taken when
printing to assure that the proper adjustment, if
any, is in effect.
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