Quadtree decomposition
qtdecomp
is appropriate primarily for square images whose
dimensions are a power of 2, such as 128-by-128 or 512-by-512. These images can
be divided until the blocks are as small as 1-by-1. If you use
qtdecomp
with an image whose dimensions are not a power
of 2, at some point the blocks cannot be divided further. For example, if an
image is 96-by-96, it can be divided into blocks of size 48-by-48, then
24-by-24, 12-by-12, 6-by-6, and finally 3-by-3. No further division beyond
3-by-3 is possible. To process this image, you must set
mindim
to 3 (or to 3 times a power of 2); if you are
using the syntax that includes a function, fun
, the
function must return 0
at the point when the block cannot be
divided further.
The qtdecomp
function divides a square image into four equal-sized
square blocks, and then tests each block to see if it meets some criterion of
homogeneity. If a block meets the criterion, it is not divided any further. If it does
not meet the criterion, it is subdivided again into four blocks, and the test criterion
is applied to those blocks. This process is repeated iteratively until each block meets
the criterion. The result can have blocks of several different sizes.