CHAPTER 7
524
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
))