A gamma correction method and system, which performs a gamma correction on an n-bit video signal to thus generate a gamma correction value. At first, a first primary index and a first sub-index are obtained by performing an index mapping on a value of the video signal. Next, a first gamma value is obtained by performing a table lookup on the first primary index and the first sub-index. Next, a second primary index and a second sub-index are obtained by performing the index mapping on the first gamma value. Next, multiple thresholds are obtained by performing the table lookup on the second primary index and the second sub-index. Finally, the value of the video signal and the multiple thresholds are compared to accordingly correct the first gamma value and generate the gamma correction value.