Nikon 4 Setting the White Point and Black Point, White-Point and Black-Point Input Levels

Enhancing Images

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 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, enhancing overall contrast without causing a corresponding loss of detail in shadows. Similarly, if the original image does not actually contain 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.

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 eyedropper tools

Automatic Contrast Adjustment

In automatic contrast adjustment, Nikon Capture automatically selects white and black points that exclude a certain percentage of the brightest and darkest pixels in the image, steepening curves for enhanced contrast (the exact percentage of pixels excluded can be specified in the Preferences dialog; 102). By default, 0.5% of the brightest and darkest pixels are excluded, producing a curve that makes optimal use of the output tone range while preserving details in shadows and highlights.

To perform an auto contrast operation, click the Auto Contrast button . The white and black points for each of the red, green, and blue channels will be modified simultaneously and the master curve will be displayed in the Curves palette (the master curve itself is unaffected by this operation). Clicking the button with the Ctrl (Windows) or option (Macintosh) key held down adjusts contrast only for the channel currently selected in the channel menu.

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