Discrete Cosine Transform

1
Discrete Cosine Transform

• The forward equation, for image A, is

• The inverse equation, for image B, is

• Here

2
Discrete Cosine Transform

• Basic idea of JPEG
• Convert image to YIQ color space
  (luminance-hue-saturation model used for TV
  transmission)
• Each color plane is partitioned into 8x8 blocks
• Apply DCT to each block
• Values are quantized by dividing with preset
  quantization values (in a table)
• Values are then rounded to nearest integer

3
JPEG Compression Interface
COMPRESSED IMAGE
8 X 8 BLOCK
ENTROPY ENCODER
DCT
QUANTIZER
(0,0)
QUANTIZERTABLE
4
Basis function of DCT