Nikon 9235 - Coolscan III Reference Manual page 68

Step 3—Setting the White Point and Black Point
The endpoints of the curve are referred to as the "white point"
and the "black point." The black point for a given channel repre-
sents the darkest shade (minimum value) for that color, the white
point, the brightest shade (maximum value). In the CMYK color
model, the black point is at the right end of the curve and the
white point at the left, while in all other color models the white
point is at the right end of the curve and the black point at the
left.
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 im-
age. Increasing the input value for the black point until it matches
the darkest shade in the image will steepen the curve, enhanc-
ing overall contrast without causing a corresponding loss of detail
in shadows. Similarly, if the original image does not actually con-
tain shades corresponding 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 final image: choosing the white-point and black-point
input levels, and selecting output levels.
Reference: The Tool Chest
White-Point and Black-Point Input Levels
Input levels for the white point and black point can be set using
any of the following three methods:
• automatic contrast adjustment
• white-point and black-point sliders
• direct sampling using the white-point and black-point eye-
dropper tools
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