Patent ID: 7733519

Claim:
A compensation method for compensating digital image data generated by a scanning module of a scanner when a luminance of a lamp is unstable, said compensation method comprising: measuring a first reference luminance value W 1 obtained by scanning a reference color region illuminated by the lamp at a first scanning position by means of the scanning module; computing a first compensating gain G 1 according to a target luminance value T and said first reference luminance value W 1 , wherein G 1 =T/W 1 ; measuring a second reference luminance value W 2 obtained by scanning said reference color region at a second scanning position by means of the scanning module; computing a second compensating gain G 2 according to said first reference luminance value W 1 , said first compensating gain G 1 and said second reference luminance value W 2 ; compensating original luminance values of the image data with said second compensating gain G 2 and computing a third compensating gain G 3 if said first compensating gain G 1 is larger than said second compensating gain G 2 and a difference between the first compensating gain G 1 and the second compensating gain G 2 is larger than a threshold value; and compensating the original luminance values of the image data with said second compensating gain G 2 without computing said third compensating gain G 3 if said second compensating gain G 2 is less than said first compensating gain G 1 and the difference between said first compensating gain G 1 and said second compensating gain G 2 is less than said threshold value.