1. A white balancing method, comprising: capturing an original image, the original image including red (R), green (G) and blue (B) color channels; computing and converting the R, G and B color channels into original color histograms; stretching the original color histograms to form stretched color histograms distributed over an entire grayscale width from 0 to 255 values; and adjusting a color of the original image based on the stretched color histograms to obtain a white balanced image; wherein in the step of computing and converting the original color histograms, a sampling length follows a formula of span m =min{(2 h , H), (2 w ,l W)}, wherein h=[log 2 H]+1, w=[log 2 W]+1, H represents a height of the original image, W represents a width of the original image, [ ] is the Gaussian symbol, ( ) is greatest common divisor function, and min{ } means selecting the minimum value.