Nikon Scanners Software Reference Manual page 165

Chapter 16
reduces the tonal range of the image data so as not to waste any of its tonal range on
light areas that are not actually present in the film.
The White Point is typically selected such that all values in the image that are
lighter than this point can be 'mapped,' or converted to white without disrupting the
quality of the image.
Selection of the White Point and Black Point is illustrated in the Master curve of
Figure 16.23. Note that all pixels in the image darker than the Black Point will be
mapped to Black, while all points lighter than the White Point will be mapped to white.
White Point
Master Curve
Black Point
Figure 16.23 The White and Black Point set in the Master curve.
When the White Point is selected, the active gamma curve is automatically adjust-
ed to reflect the Black Point.
After the White Point button is clicked, shown in Figure 16.24, position the
mouse cursor over the image in the preview window and select a pixel value to be used
as the lightest point in the image. This will be the White Point, or reference point for
darkness. In addition, the pixel's location and RGB component values will be displayed
as described in the Marker button section.
Figure 16.24 The White Point button – Macintosh and Windows.
When you decide on the pixel value you want to use as the image's White Point,
clicking the mouse forces the gamma curves to use this value as the minimum value in
the preview window. Any pixels lighter than the White Point will be set to the mini-
mum value. The result of this new curve is approximated in the preview window.
Software Reference for Scanners
The Gamma Curve Editor Dialog
Page 151