m Separated codec examples (DivX, Xvid, 3ivx) and compression standards (MPEG-2, AVC) in a sentence under "Quantization matrices" section, for added clarity.
A typical video codec works by breaking the picture into discreetdiscrete blocks (8×8 pixels in the case of MPEG<ref name="wiseman"/>). These blocks can then be subjected to [[discrete cosine transform]] (DCT) to separate out the low frequency and high frequency components in both the horizontal and vertical direction.<ref name="wiseman"/> The resulting block (the same size as the original block) is then divided by the quantization matrix, and each entry rounded. The coefficients of quantization matrices are often specifically designed to keep certain frequencies in the source to avoid losing image quality. Many video encoders (such as [[DivX]], [[Xvid]], and [[3ivx]]) and compression standards (such as [[MPEG-2]] and [[H.264/AVC]]) allow custom matrices to be used. Alternatively, the extent of the reduction may be varied by multiplying the quantizer matrix by a scaling factor, the quantizer scale code, prior to performing the division.<ref name="wiseman"/>
This is an example of DCT coefficient matrix: <!--NOTE: this matrix was generated using random numbers and the other two matricies. It may not actually work well with an iDCT. -->
