Zonal Coding

Zonal coding is the simplest transform coding scheme where each block is coded in the same way without any reference to local image content. That is, we measure statistics for the complete image and then use these to design a bit allocation and set of quantizers to code every block of the image. The bit allocation process, as discussed in chapter three, naturally leads to a zone of active coefficients and this leads to the term zonal coding. However, some researchers choose the zone first and then, using only the coefficient variances within this zone, make the bit allocation. This is a sub-optimal approach and instead we will let the bit allocation determine the zone directly.