1. At least one computer storage medium having computer executable instructions that, when executed by a computer, cause the computer to perform a method comprising: coding a coefficient representative of a chrominance component corresponding to an (x, y) coordinate pair into a symbol; computing a plurality of context events based upon a corresponding coefficient of a luminance component at the (x, y) coordinate pair and at least one other coefficient of another luminance component having a coordinate relationship with the (x, y) coordinate pair, wherein the computing the plurality of context events comprises comparing coefficients that have adjacent horizontal, vertical and diagonal relationships with the corresponding coefficient against a threshold value, and wherein the computing the plurality of context events further comprises separately comparing each horizontally-related coefficient against the threshold value and logically combining a result of each horizontally-related luminance coefficient comparison to obtain one value for one context event, and separately comparing each vertically-related coefficient against the threshold value and logically combining a result of each vertically-related coefficient comparison to obtain another value for another context event, and separately comparing each diagonally-related coefficient against the threshold value and logically combining a result of each diagonally-related coefficient comparison to obtain yet another value for yet another context event; comparing the coefficients against a decreasing threshold value until the coefficient representative of the chrominance component meets the threshold value; halving the threshold value into a new threshold value when the coefficient representative of the chrominance component does not meet the threshold value; and associating the symbol with the context events for context-based arithmetic coding.