Operation Manual

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The Tool Chest — Curves

Channel Selection Shortcuts

The current channel can also be selected using the following shortcuts:

• Ctrl ~ (Windows)/ ~ (Macintosh)

Master channel (RGB)

• Ctrl 1 (Windows)/ 1 (Macintosh)

Red channel (RGB)

• Ctrl 2 (Windows)/ 2 (Macintosh)

Green channel (RGB)

• Ctrl 3 (Windows)/ 3 (Macintosh)

Blue channel (RGB)

Step 2—Channel Selection

The channel menu is used to select compo-

nents of the current color model for editing.

Select the master curve to modify tones for

all channels in the image. In the RGB color

model, the red, green, and blue curves can

be modiﬁ ed separately. The histogram shows tone levels for

the selected chan nel only.

When the master curve is selected, the auto-contrast but-

ton and white-point and black-point eye drop per tools apply

simultaneously to all of the red, green, and blue curves (the

master curve is un af fect ed). When one of the red, green,

and blue curves is selected, these controls can be used to

edit only the se lect ed curve.

Step 3—Setting White and Black Points

The endpoints of the curve are referred to as the “white

point” and the “black point.” The black point for a given

channel represents the darkest shade (minimum value) for

that color, the white point, the brightest shade (maximum

value). By default, the input and output values for the black

point are zero. The darkest shade in the input image may

however be greater than zero, with the result that a portion

of the curve is dedicated to reproducing tones not actually

present in the image. Increasing the input value for the black

point until it matches the darkest shade in the image will

steepen the curve, en hanc ing overall contrast without caus-

ing a corresponding loss of detail in shadows. Similarly, if the

original image does not actually contain shades correspond-

ing to the maximum value, the white point can be lowered

to match the brightest shade in the image.

There are two steps to selecting a white point and black

point for the ﬁ nal image: choosing the white-point and

black-point input levels, and selecting out put levels.