1. One or more processor-accessible tangible media comprising processor-executable instructions that, when executed, direct a device to perform acts comprising: identifying textual blocks from among multiple blocks of an image; and compressing the textual blocks by implementing the following acts for each textual block: decomposing the textual block into base colors and an index map, the index map having multiple index values that each reference a base color to represent at least part of a textual block; converting the index map by implementing the following acts for at least a portion of the multiple index values of the index map: generating a coding context that matches the index value based on one or more other index values of the index map that are proximate to the index value and with reference to a set of predetermined contexts; and remapping the index value responsive to a symbol that corresponds to the index value and that is included in the matching coding context; and encoding the converted index map to produce a compressed index map.