http://www.digitalcameraworld.com AUGUST 2019 DIGITAL CAMERA^79
TOOL SCHOOL1
Parametric
and Point tabs
The Tone Curve Panel
offers two methods
for adjusting the curve line. The
Parametric tab is better for
beginners, as it offers sliders that
alter the highlights, lights, darks
and shadows. If you’re comfortable
using Curves, the Point tab is by
far the better option: it gives you
the freedom to add control points
along any part of the line, including
at the very top or bottom.3
S-curves
and contrast
An S-curve is the best
way to add contrast
and punch in Photoshop. Simply
drag a point upwards near the
top of the line, then drag a second
point downwards near the bottom,
creating an S-shape. The more
pronounced the S, the greater the
contrast. Making the S top-heavy
will lift the highlights but have less
effect on the shadows; a bottom-
heavy S will deepen the shadows.2
The curve
The curves actually
begins as a straight
diagonal, representing
the image in its current state. By
altering the line, you can affect the
tonal range – from shadows on the
left to highlights on the right. At
any point where you push the line
above the diagonal, that part of the
tonal range will get lighter, with the
curve ensuring gentle transitions
between our control points. Push
it below, and things get darker.4
Control points
Alter the curve by
adding control points
along it, then use them
to lift or lower the brightness in
different parts of the tonal range.
You can add up to 14 anchor points,
but you rarely need more than four.
As well as using control points to
move the line up or down, they
can be equally useful for anchoring
parts of the line back along the
original diagonal slope, thereby
ensuring that part of the tonal
range is unaffected.6
Red, green and
blue channels
This lets you target
the red, green and
blue channels for precise colour
changes. Dragging the red curve
upwards adds in more red, while
down adds cyan – the opposite
of red. Similarly, decreasing green
introduces magenta, and dropping
blue results in yellow. You can
create interesting colour shifts
by tweaking the very top and
bottom points of the curves
on these three colour channels.5
Input and
Output boxes
These show the position
of your selected control
point. Input shows the part of the
tonal range between 0-255 that
you’re altering – in other words,
the X axis. Output shows how
much the point has been altered by
moving it up or down – the Y axis.
For example, if you make a point
in the centre of the box at Input
127, then drag it all the way up so
Output is 255, all the pixels from
124-255 are made fully white.