03/18/2003
15-462 Graphics I
43
Discrete Cosine Transform
•Used for lossy compression (as in
JPEG)
•JPEG (Joint Photographic Expert
Group)
–Subdivide image into n £ n blocks (n = 8)
–Apply discrete cosine transform for
each block
–Quantize, zig-zag order, run-length
code coefficients
–Use variable length coding (e.g.
Huffman)
•Many natural images can be compressed
to 4 bits/pixels
with little visible error
