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Chapter 3: Correcting Images in the RGB Color Space 3-11
The gradation curve (black) defines how tone compression is handled. The hori-
zontal axis shows the input density while the vertical axis displays the output
density.
The points (called “anchor points”) are located, from left to right, at the follow-
ing values: highlights, quarter tones, midtones, three-quarter tones, and shadows.
By selecting an anchor point and dragging it up or down, you can alter the gra-
dation value for that point.
The lock icon at the bottom left corner of the grid is open by default. By clicking
on it, you can lock the anchor points on the curve. This allows you to move the
points individually without affecting the others. Locking anchor points is useful
for fine-tuning the gradation curve.
Note: Adjustments in the gradation curve
change the input-to-output tonal compression.
For example, moving the three-quarter tone
point down expands the shadow area of the
image by starting the three-quarter tone range
at a lower optical density.
Note: Every original, film or print, has a specific
density range which defines the points where
the image data starts and ends. This density
range is measured on an optical density scale of
0 (lowest) to 4 (highest).
The “output density range” is usually set to different values than the input range.
The default output density value is 2.7, the maximum density monitors are capa-
ble of displaying. Knowing the density range of your intended output device and
entering that value in the RGB Control window helps optimize the quality of the
final image.
Note: If you are unsure of which value to use,
keep the value 2.7. If your output device is a
film recorder, values of 3.0 or higher may be
advisable.