1. A method for applying sub-pixel converting algorithm on the display of a display device, comprising the steps of: a. extracting, by the display device, a sub-pixel W′ from three input original pixels (RGB) 3 of the display, wherein W′=f(Y 1 min , Y 1 max , Y 2 min , Y 2 max , Y 3 min , Y 3 max ), Y 1 min and Y 1 max respectively denote the minimum value and maximum value of luminance of R 1 G 1 B 1 , Y 2 min and Y 2 max respectively denote the minimum value and maximum value of luminance of R 2 G 2 B 2 , and Y 3 min and Y 3 max respectively denote the minimum value and maximum value of luminance of R 3 G 3 B 3 ; b. removing, by the display device, the sub-pixel W′ from the original pixel R i G i B i (i=1, 2, 3) to obtain R i *G i *B i *(i=1, 2, 3); c. calculating sub-pixels R 1 ′ and R 2 ′ by using R 1 *, R 2 *, R 3 * in (R i *G i *B i *) i=1,2,3 , calculating a sub-pixel G 1 ′ and G 2 ′ by using G 1 *, G 2 *, G 3 *, and calculating sub-pixels B 1 ′ and B 2 ′ by using B 1 *, B 2 *, B 3 *, wherein 
 R 1 ′=g 1 (R 1 *, R 2 *), R 2 ′=g 2 (R 2 *, R 3 *); 
 G 1 ′=g 1 (G 1 *, G 2 *), G 2 ′=g 2 (G 2 *, G 3 *); 
 B 1 ′=g 1 (B 1 *, B 2 *), B 2 ′=g 2 (B 2 *, B 3 *); and rendering sub-pixels R 1 ′, R 2 ′, G 1 ′, G 2 ′, B 1 ′, B 2 ′, W′ and on the display.