storing in a memory the method for selecting conditioning states to be used in the context model for coding the source;

processing on a processor the method for selecting conditioning states to be used in the context model for coding the source;

recognizing a plurality of potential conditioning states;

partitioning the plurality of potential conditioning states into groups of conditioning states according to a rule, at least one of the groups including a plurality of conditioning states, wherein the potential conditioning states includes one of:

a plurality of original conditioning states representing possible combinations of context events; and

a plurality of quantized conditioning states quantized from the potential conditioning states or a plurality of previously quantized conditioning states;

selecting at least one of the groups of conditioning states to be used in the context model; and

forming a plurality of layers by:

collecting the conditioning states in a layer; and

quantizing at least a portion of the conditioning states in the layer to create a next layer of collective conditioning states, wherein quantizing the conditioning states in the layer to create the next layer includes:

quantizing each of a plurality of pairs of conditioning states in the layer as a collective conditioning state in the next layer;

when there is a remaining conditioning state in the layer after each of the pairs of conditioning states have been quantized, including the remaining conditioning state in the next layer; and

outputting the selected conditioning states to be used in the context model for coding a source.