
Figure 38.4
An 8x8 array of
luma samples from an
image is shown. This 8x8
array is known in JPEG
terminology as a
block.
Figure 38.5
DCT tends
to
concentrate
the power of the
image block into low-frequency
DCT coefficients (those coeffi-
cients in the upper left-hand
corner of the matrix). No infor-
mation is lost at this stage. The
DCT is its own inverse, so
performing the DCT on these
transform coefficients would
reconstruct the original samples
(subJect only to roundoff error).
If implemented directly according to these equations,
an 8x8 DCT requires 64 multiply operations (and 49
additions) for