
Figure 7.14 shows an example of the two-dimensional DWT of an image.
Since the sum of all of the coefficients in each detail set is zero, the average value
(which is zero) is adjusted to 128 (medium gray), and the dynamic range is
adjusted to fit the 8-bit grayscale, for ease of visualization. Notice that the detail
coefficients (high-frequency subbands) have large magnitudes near edges and
details in the image and small magnitudes at locations where no prominent high-
frequency features reside. This sparse representation, also known as energy com-
paction, is quite useful for many applications, especially image compression.
Notice also that the edges ...