Image Processing Reference
In-Depth Information
1
0.9
1
1
0.8
0.8
0.7
0.8
0.6
0.6
0.6
0.5
0.4
0.4
0.4
0.3
0.2
0.2
0.2
0.1
0
0
0
0
1
1
0.2
0.2
0.8
0.8
0.6
0.6
0.4
0.4
0.4
0.4
0.2
0.2
0.6
0.6
Green
0
0
Red
0.8
1
0.8
Green
Red
Fig. 2.6. (
Left
) The isocurves of the HSB coordinates when the saturation is 0.5. The
nine twisted hexagons represent colors for different values of brightness. (
Right
) The same
isocurves viewed through the brightness axis, (1
,
1
,
1)
T
2.6 HSB: Hue, Saturation, Brightness Color Space
Whereas the colors of the RGB space are usually produced by varying three colored
light emitters, it is not easy for humans to interpret the thus-obtained colors. Derived
from the RGB space, the
hue
,
saturation
and
brightness
space,
4
HSB color space
is, by contrast, intuitive. It interprets the color in a way that resembles artists' way of
describing or perceiving it. Assuming to have a color with the components (
r, g, b
)
T
,
in the RGB space, the HSB representation of this color yields
⎧
⎨
g−b
max
−
min
)
π
3
(
,
if
r
=max
,
b−r
max
−
min
)
π
3
H
=
(2 +
,
if
g
=max
,
(2.7)
⎩
r−g
max
−
min
π
3
(4 +
,
if
b
=max
,
S
=max
−
min
(2.8)
B
=max
(2.9)
where max and min refer to the largest and smallest values of
r, g, b
, respectively.
The HSB coordinates resemble
5
the cylindrical coordinates of the RGB color point
around the
brightness axis
, the main diagonal represented by the direction (1
,
1
,
1)
T
of the
RGB cube
, although there are significant differences. First, the coordinate
curves and sufaces of the HSB colors are contained within the RGB cube, but they are
neither cylindrical nor circular. By that we mean the curves and surfaces generated
when one or two of the variables H,S,B of the color is kept constant, i.e., the isocurves
and surfaces of the coordinate transformation above. They are curves that generate
4
Another name for this is hue, saturation, value
(HSV) color space
.
5
There are also studies in which HSB coordinates are presented as cylindrical coordinates,
although the “hexagon” version here appears to be the most common, because of its conver-
sion equations using only arithmetic operations, which result in simple graphics hardware.
