SECTION 4.8
345
Images
that
x
min
<
x
max
and clips
x
values to this domain so that
y
=
y
min
for all
x
≤
x
min
,
and
y
=
y
max
for all
x
≥
x
max
.
For a
Decode
array of the form
[
D
min
D
max
]
, this can be written as
y
=
Interpolate
(
x
,
0
,
2
–
1
,
D
min
,
D
max
)
D
max
–
D
min
⎞
⎛
-
=
D
min
+
⎜
x
×
------------------------------
⎟
n
⎝
⎠
2
–
1
n
where
n
is the value of
BitsPerComponent
x
is the input value, in the domain 0 to 2
n
−
1
D
min
and
D
max
are the values specified in the
Decode
array
y
is the output value, to be interpreted in the image’s color space
Samples with a value of 0 are mapped to
D
min
, those with a value of 2
n
−
1 are
mapped to
D
max
, and those with intermediate values are mapped linearly be-
tween
D
min
and
D
max
Decode
arrays for use with the
various color spaces. For most color spaces, the
Decode
arrays listed in the table
map into the full range of allowed component values. For an
Indexed
color space,
the default
Decode
array ensures that component values that index a color table
are passed through unchanged.
TABLE 4.40 Default Decode arrays
COLOR SPACE
Decode
ARRAY
[ 0.0 1.0 ]
[ 0.0 1.0 0.0 1.0 0.0 1.0 ]
[ 0.0 1.0 0.0 1.0 0.0 1.0 0.0 1.0 ]
[ 0.0 1.0 ]
[ 0.0 1.0 0.0 1.0 0.0 1.0 ]
[ 0 100
a
min
a
max
b
min
b
max
]
where
a
min
,
a
max
,
b
min
, and
b
max
correspond to the values in the
Range
array of the image’s color
DeviceGray
DeviceRGB
DeviceCMYK
CalGray
CalRGB
Lab
space