Manual

173
Enhancing Images
Sampling the Image for White Point or Black Point
The white point or black point can be set by directly sampling the image, allowing you 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, eliminating 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 im-
age. 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 simultaneously; the master curve itself is unaffected.
To sample the white point, click the White Point 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 cursor will return to its original shape, and the image will
automatically be altered to refl ect the new value for white point.
To sample the image for the black point, click the Black Point 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.
Setting the White Point or Black Point for the Current Channel
By default, sampling sets the white point or black point for all channels and displays the master chan-
nel. To set the white point, midpoint, or black point for the current channel only, sample the image
while holding down the Ctrl key (Win dows) or option key (Macintosh) on the keyboard. Note that
midpoint can not be sampled for a single channel; regardless of the channel currently selected in the
channel menu, sampling the image for midpoint always sets the mid point for all chan nels and dis plays
the master chan nel.