Operation Manual

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The Tool Chest — Curves

Sampling the Image for White Point or Black Point

The white point or black point can be set by directly sam-

pling the image, allowing the user to choose the pixels that

will be used to set the maximum (white point) or minimum

(black point) output value. This makes it possible to set the

black point by matching it to a pixel in the darkest part of

the image containing detail you want to preserve, eliminat-

ing details in darker areas that are not important to the ﬁ nal

image. Similarly, you can match the white point to a pixel in

the brightest area of the image containing details important

to the ﬁ nal image. While direct sampling can be used with

any channel, it is most effective when used with the master

curve. When the master curve is selected, sampling will set

the white or black point for red, green, and blue curves si-

multaneously; the master curve itself is unaffected.

Setting the White or Black Point for the Current Channel

By default, sampling sets the white point or black point for all channels

and displays the master curve. To set the white point or black point for

the current channel only, press the Ctrl key (Win dows) or option key

(Macintosh) while clicking the or button. To modify brightness

and contrast without affecting color balance, select the master channel

and press Ctrl (Win dows) or option (Macintosh) while clicking the

or button.

To sample the white point, click the button. When the

cursor is moved over the active image, it will take the shape

of an eyedropper. Move the cursor over the image to ﬁ nd

the pixel that you want to use to set the white point, keeping

an eye on pixel level display in the “Information” palette to

identify pixels with high input values. With the cursor over

the target pixel, click the mouse button. The input value

for the selected pixel will be used as the input value for the

white point. The image will automatically be altered to re-

ﬂ ect the new value for white point and the master curve will

be displayed in the “Curves” palette.

To sample the image for the black point, click the

button

and move the eye drop per cursor over the image until you

ﬁ nd the point that you want to use to set the min i mum input

value, then click the mouse button to select the black point.