about
Curves
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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