SECTION 7.2
521
Basic Compositing Computations
NAME
RESULT
Screen
Multiplies the complements of the backdrop and source color values, then complements
the result:
B
(
c
b
,
c
s
) =
1
–
[ (
1
–
c
b
) × (
1
–
c
s
) ]
=
c
b
+
c
s
–
(
c
b
×
c
s
)
The result color is always at least as light as either of the two constituent colors. Screening
any color with white produces white; screening with black leaves the original color un-
changed. The effect is similar to projecting multiple photographic slides simultaneously
onto a single screen.
Overlay
Multiplies or screens the colors, depending on the backdrop color value. Source colors
overlay the backdrop while preserving its highlights and shadows. The backdrop color is
not replaced but is mixed with the source color to reflect the lightness or darkness of the
backdrop.
B
(
c
b
,
c
s
) =
HardLight
(
c
s
,
c
b
)
Darken
Selects the darker of the backdrop and source colors:
B
(
c
b
,
c
s
) =
min
(
c
b
,
c
s
)
The backdrop is replaced with the source where the source is darker; otherwise, it is left
unchanged.
Lighten
Selects the lighter of the backdrop and source colors:
B
(
c
b
,
c
s
) =
max
(
c
b
,
c
s
)
The backdrop is replaced with the source where the source is lighter; otherwise, it is left
unchanged.
ColorDodge
Brightens the backdrop color to reflect the source color. Painting with black produces no
changes.
⎧
min
(
1
,
c
b
⁄ (
1
–
c
s
)
)
B
(
c
b
,
c
s
)
=
⎨
⎩
1
ColorBurn
if
c
s
<
1
if
c
s
=
1
Darkens the backdrop color to reflect the source color. Painting with white produces no
change.
⎧
1
–
min
(
1
, (
1
–
c
b
) ⁄
c
s
)
B
(
c
b
,
c
s
)
=
⎨
⎩
0
if
c
s
>
0
if
c
s
=
0