Page 256 - Digital Analysis of Remotely Sensed Imagery

218 Cha pte r S i x

histogram of both images should be very similar. The matching is con-
ceptually illustrated in Fig. 6.10. The two photographs (Fig. 6.10a and b)
to be histogram matched cover the same geographic area. They have a
temporal separation of 20 years (from 1978 to 1997). Histogram match-
ing bears a high resemblance to histogram equalization. The only dif-
ference is that the second cumulative histogram comes from the master
image (Fig. 6.10b) instead of the equalized one in this case. Because of
the changed illumination conditions and the environment, the histo-
gram-matched image (Fig. 6.10c) highly resembles the master image,
but is not identical to its radiometry.

Histogram
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0 256
(a)

Histogram
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0 256
(b)

Histogram
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(c)
FIGURE 6.10 An example of histogram matching. (a) Slave image and its
histogram; (b) master image and its histogram; (c) the output image whose
histogram has been matched to that of the master image (b).