Patent ID: 6944336

Claim:
A fast gamma correction method for an image reading apparatus with a color correction function and a plurality of normalized output pixel data after correction Y quantified by n-bits into 2 n intervals, comprising the following steps: a. combining the 2 n intervals to M merged intervals, comprising the following steps: a0: set k=0; a1: set h=k; a2: set k=k+1; a3: if k=2 n , stop; a4: if s is within (h,k), and all X T , T=0 . . . 2 m −1, in (G −1 (T s ), G −1 (T s+1 )), are equal to all X T , T=0..2 m −1 in (F −1 (h,k) (T s ), F −1 (h,k) (T s+1 )), back to step a2; a5: merging (T h , T h+1 )˜(T k−1 , T k ) into (T h , T k ), and recoding F (h,k) (.): and a6: back to step a1; wherein m: resolution of normalized input data, n: resolution of normalized output data, Y=G(X): realistic color correction function, F (h,k) (.) fitting function in interval (T h , T k ), and M≦2 n ; b. reading a normalized input pixel data X and locating which merged interval the input pixel data X lies in, wherein threshold values of the X coordinate can be obtained by inversely mapping threshold values of the Y coordinate; and c. finding the normalized output pixel data after correction Y by a fitting function in the merged interval and using the normalized input pixel data X for substitution.