A method of a sensing device, comprising steps of emitting, by a light source of the sensing device, a light pulse in each of n cycles; measuring, by a single photon avalanche diodes array of the sensing device, a time-of-flight value with a resolution of m in each of the n cycles to generate n raw data frames based on a reflected light of the light pulse; performing, by a pre-processing circuit of the sensing device, a pre-processing operation to n raw data frames to generate k pre-processed data frames, wherein m, n and k are natural numbers, and k is smaller than n; and generating, by post-processor of the sensing device, a histogram according to the k pre-processed data frames and analyzing the histogram to output a depth result.