Introduction
If you ever need to develop a JPEG application that uses quantization tables, theres probably a little bit of information you need to know here. Quantization tables are used by the JPEG application after DCT, and are applied against chrominance and luminance tables respectively.
Default Tables
The default JPEG quality (Q) facator is %75, and usually is settable in most JPEG applications. The following are the values used in the luminance and chrominance tables.
DC Component Only
You may wish to set only DC component of the quantization table, and this simply means setting the first element of both tables to the user required value. See the sample below.
Constant Values
The last option you might choose is a constant value. This sets all elements of the table to the same value, although you could have different constant values for luminance and chrominance.
Zig Zag Ordering
Normally zig zag ordering is done after quantization, but your application may require the quantization table to be in zig zag order. The zig zag starts from the upper left and ends at the bottom right, just like the picture below.
In this case I’m showing the default luminace quantization table; and thus the zig zag order would be as follows:
16, 11, 12, 14, 12, 10, 16, 14, 13, 14, 18, 17, 16, 19, 24, 40, 26, 24, 22, 22, 24, 49, 35, 37, 29, 40, 58, 51, 61, 60, 57, 51, 56, 55, 64, 72, 92, 78, 64, 68, 87, 69, 55, 56, 80,109, 81, 87, 95, 98,103,104,103, 62, 77,113, 121,112,100,120, 92,101,103, 99
Alvin Bunk 