Six step process
– Color space transform RGB to YCbCr
– Downsampling
– Block Splitting
– Discrete Cosine Transform
– Quantization (where the magic happens)
– Encoding (lossless compression)

Quantization Tables
Table used to control lossy compressiion
! Up to four sets of tables
– 64 values in each table
! Vallue for each piixel is divided by a table value
– Decimals thrown away
– Decimal loss leads to image quality loss
! 124 // 50 --> 2
! When decompressed 2*50 = 100


Independent JPEG Group (IIJG) Tablles
– Last updated 1998
! Scalliing method uses qualiity factor Q
! Q can be between 1 and 100
! S = (Q < 50) ? 5000//Q : 200 – 2Q
! Ts[ii] = (S * Tb[ii] + 50) // 100
! IInteger math
– No decimals, information lost
! Scalliing wiith Q=50 means no change

IJG Standard Table

All ones
– No data
! Standard Tablles
! Two IJG
! Extended Standard Tablles
! Three IJG
! Custom Fiixed Tablles
! Adobe Photoshop
! Custom Adaptiive Tablles

Set of known quantiizatiion tablles
– 99 Standard Tables
– 99 Extended Standard Tables
– Tables from Adobe Photoshop

use calvin from DOD to find tables.