286 CHINESE OPTICS LETTERS / Vol. 8, No. 3 / March 10, 2010
Robust color segmentation algorithms in illumination
variation conditions
Jinhui Lan (777777)
∗
and Kai Shen ( ppp)
Department of Measurement and Control Technologies, School of Information Engineering,
University of Science and Technology Beijing, Beijing 100083, China
∗
E-mail: jh.lan@263.net
Received June 15, 2009
Changing illumination condition can change the result of image segmentation algorithm and reduce the
intelligent recognition rate. A novel color image segmentation method robust to illumination variations
is presented. The method is applied to the skin segmentation. Based on the hue preserving algorithm,
the method reduces the dimensionality of the red-green-blue (RGB) space to one dimension, while keeping
the hue of every pixel unchanging before and after space transformation. In the new color space, the skin
color model is established using Gaussian model. Experimental results show that the method is robust to
illumination variations, and has low computational complexity.
OCIS co des: 100.2000, 100.3008.
doi: 10.3788/COL20100803.0286.
Color segmentation is an essential, critical, and prelimi-
nary process in a lot of vision-based tasks such as visual
tracking, human-computer interaction (HCI), human-
robot interaction (HRI), vision-based robotics, visual
surveillance, and so forth, because color is an effective
and robust visual cue for characterizing an object from
the others. Recently, there has been a growing interest
in the skin segmentation, which aims at detecting human
skin regions in an image.
However, changing illumination condition can change
the characteristics of a color, and limit the applications
of the color segmentation
[1]
. Therefore, a lot of re-
searches have been carried out for invariant detection of a
color under illumination-variation conditions. Static skin
model based methods were adopted
[2−5]
, which firstly
selected an appropriate color space. The color space
transformation has been assumed to increase separabil-
ity between skin and non-skin classes to increase sim-
ilarity among different skin tones. Then a model of
skin color in the selected color space is established to
decide whether a pixel belongs to a skin region. The
color space mainly includes normalized red-green (RG)
[2]
,
hue-saturation-value (HSV) (hue-saturation-illumination
(HSI))
[5]
, YCrCb
[6]
, YIQ
[7]
, YES
[8]
, etc. The skin color
model includes single Gaussian model
[2]
, Gaussian mix-
ture models
[3]
, Gaussian mixture models considering in-
tensity information
[5]
, etc. Cho et al. and Soriano
et al. used dynamic learning based methods for color
segmentation
[9,10]
. These methods dynamically allocate
a color through various illumination conditions while
those models are updated for every image sequence.
Adaptive skin color filter and ‘skin locus’ adaptive skin
color modeling are two typical methods of dynamic learn-
ing based methods.
In this letter, a novel color image segmentation method
which is robust to illumination variations is proposed.
Since RGB space is the most common space to represent
color images, and HSI space can separate the chromi-
nance and luminance in a color image to a certain extent,
we consider both the characteristics of RGB space and
HSI space, and reduce the dimensionality of the RGB
space to one dimension while preserving the hue of ev-
ery pixel in the image before and after space transforma-
tion constant by hue-preserving algorithm. Therefore,
1D threshold can be used to sub divide the color image.
Experimental result verifies that the proposed method is
not only robust to the changing illumination condition,
but also more efficient in computation efforts.
Hue preservation is necessary when converting colors
from one color space to another. Distortion may o ccur
if hue is not preserved. The hues of a pixel in the scene
before and after the transformation should be the same
for a hue preserving transformation. First of all, a gen-
eral hue-preserving method between RGB space and HSI
space is introduced for color image segmentation.
The conversion equations from the RGB space to HSI
space are noted as
H = arctan
Ã
√
3 (G − B)
(R − G) + (R − B)
!
S = 1 −
3 [min (R, G, B)]
(R + G + B)
I =
1
3
(R + G + B)
. (1)
In general, color images are stored and viewed using
RGB space. To pro cess an image for segmentation in
HSI space, the image needs to be transformed. As can
be seen from Eq. (1), this transformation is computation-
ally costly
[11]
, and the inverse coordinate transformation
has to be implemented for displaying the images.
Two hue-preserving operations, scaling and shifting,
were introduced in Ref. [12] for luminance and saturation
processing. Using these two operations, hue-preserving
method for color image segmentation is developed.
We denote the grey values for R, G, and B components
of an image pixel I by a vector x, where x = (x
1
, x
2
, x
3
),
x
1
, x
2
, and x
3
correspond to the red, green, and blue
pixel values, respectively. That is, 0 ≤ x
k
≤ 255, k = 1,
2, and 3.
Scaling the vector x to x
0
by a factor α > 0 is defined as
1671-7694/2010/030286-04
c
° 2010 Chinese Optics Letters