1. An apparatus used in video encoding comprising: a processor configured to: generate a prediction block for a current block; compute a difference between the current block and the prediction block to generate a residual block, wherein the residual block comprises a plurality of residual values; and if the plurality of residual values includes at least one non-zero residual value comprising at least one sign and at least one residual level, perform entropy encoding on the at least one sign; and perform entropy encoding on the at least one residual level, wherein one non-zero residual value comprises one sign and one residual level, wherein the plurality of residual values includes at least one non-zero residual value, wherein entropy encoding of a sign is based on spatial correlation between the sign and one or more previously encoded signs, and wherein the plurality of residual values includes at least three non-zero residual values, wherein the three non-zero residual values have a first, second, and third signs, wherein performing entropy encoding on the first, second and third signs follows an encoding order, wherein the second sign immediately follows the first sign in the encoding order, wherein the third sign immediately follows the second sign in the encoding order, wherein performing entropy encoding on the third sign comprises using a context-adaptive binary arithmetic coding (CABAC) algorithm, wherein the CABAC algorithm has four context models selectable by an index, wherein the index equals 0, if the first and second signs are (+, +); 1, if the first and second signs are (+, −); 2, if the first and second signs are (−, +); and 3, if the first and second signs are (−, −).