Page 192 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes 11.4.2 interpixel redundancy
Consider the images shown in Figures 11.1 (a) and (b). As Figs. 11.1 (c) and (d) shows, these images
have virtually identical histograms. Note also that both histograms are trimodal, indicating the
presence of three dominant ranges of grey-level values. Because the grey levels in these images
are not equally probable, variable-length coding can be used to reduce the coding redundancy
that would result from a straight or natural binary encoding of their pixels. The coding process,
however, would not alter the level of correlation between the pixels within the images. In other
words, the codes used to represent the grey levels of each image have nothing to do with the
correlation between pixels. These correlations result from the structural or geometric relationships
between the objects in the image.

figure 11.1: two images and their Grey-level Histograms and
Normalized Autocorrelation Coefficients along One Line

b
a
( ) ( )
p × 10 2 p × 10 2
r
r
1.6 1.8
1.2
1.2
0.8
0.6
0.4

0.0 0.0
0 128 r k 225 0 128 r k 225
d
( ) ( )
c
 
1.0 1.0
0.8 0.8
0.6 0.6
0.4 0.4

0.2 0.2
0.0 0.0
0 5 0 n 100 0 5 0 n 100
e
( ) ( ) f

186 LoveLy professionaL University