Operation Manual

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The Tool Chest — Curves

The Curve Edit Display

Although values for input and output in the “Curves” palette range from

zero to 255 (eight-bit pre ci sion, familiar to users of other image editing

software), the results of any changes to curves are calculated at a preci-

sion of sixteen bits. This allows images scanned at twelve and fourteen

bits to be modiﬁ ed without lowering the quality of the output.

Input is plotted along the horizontal axis, with shadows (the

dark areas of the image) to the left, high lights (the bright

areas of the image) to the right, and mid-tones in between.

The left end of the axis marks the minimum possible value

for colors in the selected channel (zero, or no color), the right

end the maximum value. In the case of the master curve, the

minimum value represents areas of the input image that are

a true black; the maximum value represents areas that are a

true white. Output is plotted along the vertical axis, with the

minimum possible output value (again, zero, or no color) at

the bottom and the maximum output value at the top.

Current channel

Curve edit display

Curves

Fine-Tuning Color, Contrast, and Brightness

The “Curves” palette is used to adjust brightness, contrast,

and color in speciﬁ c por tions of the tone range (highlights,

mid-tones, and shadows). The main editing tool in the

“Curves” palette is the curve edit display, which contains a

curve showing the relationship between input (the tones in

the original image) and output (how the tones in the input

will be represented in the ﬁ nal image). Separate curves

control the re la tion ship between input and output for the

image as a whole (the “master curve”) and for each of the

com po nent colors, or “channels,” in the current color model

(red, green, and blue in the case of the RGB color model).

The default curve in each case is linear, meaning that tones

will be output exactly as they are input.

The “Curves” Palette

The “Curves” palette can be used in both the scan window and in im-

age windows.

Output

Input

Shadows

Mid-tones

Highlights