Page 116 - Digital Analysis of Remotely Sensed Imagery

Storage of Remotely Sensed Data 87

header information is followed by the image content of the first band.
This sequence is repeated for each of the multispectral bands. This
method of image storage is the most intuitive and practical, but is
difficult to deal with subscene images. This storage form has the
advantage in certain image analyses, such as display of individual
bands on the computer screen. In this case BSQ is preferable insofar
as one does not have to read past ancillary data in an image stack. On
the other hand, this form is ill suited to other analyses, such as image
classification, in which multiple pixels at the same location need to be
examined simultaneously. Other forms of image storage are more
efficient in this regard.
In the BIL form multiple bands are stored line by line. For instance,
the first line of the first band is recorded, followed by the first line
of the second band, and the first line of the third band until the first
line of the last band. Then the second line of the first band is stored,
followed by the same line in the second, third, … , and the nth band
(Fig. 3.2).
The BIP form is very similar to that of BIL except the value
associated with a pixel is stored sequentially in all bands (Fig. 3.3). All
pixels at a certain location are stored at a close proximity to one
another. This kind of data storage is advantageous when these pixels
are examined at the same time, such as during a classification.
However, it is an inefficient form of storage if only one band is
examined, such as image contrast enhancement in which a single
band forms the focus of analysis.

5824110554599924311062234
4462447715523556533488958
8200334455880113400966223

33124477867714542255734

FIGURE 3.2 The BIL format of image storage.

5585244519190922424314140

4662542437575165538384280
8093534141535480800961622
42437373862727515475344

FIGURE 3.3 The BIP format of image storage.