Quantization Type: What is a Quantization Matrix?
The quantization matrix is the 8 by 8 matrix of step sizes (sometimes called quantums) – one element for each DCT coefficient. It is usually symmetric. Step sizes will be small in the upper left (low frequencies), and large in the upper right (high frequencies); a step size of 1 is the most precise. The quantizer divides the DCT coefficient by its corresponding quantum, then rounds to the nearest integer. Large quantums drive small coefficients down to zero. The result: many high frequency coefficients become zero, and therefore easier to code.” To put it short: It’s the lossy filter by which you achieve higher compressibility by losing detail. The amount of detail lost is determined by the values of each individual quantum. More theory about the technical process behind it: http://www.ece.purdue.edu/~ace/jpeg-tut/jpegtut1.html http://www.mpeg.org/MPEG/MSSG/tm5/Ch7/Ch7.html http://www.cmlab.csie.ntu.edu.tw/cml/dsp/training/coding/jpeg/jpeg/encoder.htm http://www.acm.org/crossroads/xrds
