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                                                         524
             CHAPTER 7                                                                  Transparency



             In the following function, the subscripts min, mid, and max refer to the color
             components having the minimum, middle, and maximum values upon entry to
             the function.
             SetSat(C, s)
                   if C max > C min
                       C mid = ( ( ( C mid – C min ) × s ) ⁄ ( C max – C min ) )
                       C max = s
                   else
                       C mid = C max = 0.0
                   C min = 0.0
                   return C


                                 TABLE 7.3 Standard nonseparable blend modes
NAME                    RESULT

Hue                     Creates a color with the hue of the source color and the saturation and luminosity of the
                        backdrop color.
                           B ( C b, C s ) = SetLum(SetSat(C s, Sat(C b)), Lum(C b))

Saturation              Creates a color with the saturation of the source color and the hue and luminosity of the
                        backdrop color. Painting with this mode in an area of the backdrop that is a pure gray (no
                        saturation) produces no change.
                           B ( C b, C s ) = SetLum(SetSat(C b, Sat(C s)), Lum(C b))

Color                   Creates a color with the hue and saturation of the source color and the luminosity of the
                        backdrop color. This preserves the gray levels of the backdrop and is useful for coloring
                        monochrome images or tinting color images.
                           B ( C b, C s ) = SetLum(C s, Lum(C b))

Luminosity              Creates a color with the luminosity of the source color and the hue and saturation of the
                        backdrop color. This produces an inverse effect to that of the Color mode.
                           B ( C b, C s ) = SetLum(C b, Lum(C s))

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