Patent ID: 6915022

Claim:
An image preprocessing method for processing an input image having a plurality of pixels arranged in an array form to increase the accuracy of a subsequent face detection, a pixel at column m and row n of the input image having an image value f(m,n), the preprocessing method comprising the steps of: (A) for each pixel (m,n) of the input image, determining a sum TOP a (m,n) of PN pixels on row n−a closest to the pixel (m,n), and a sum BOT a (m,n) of the PN pixels on row n+a closest to the pixel (m,n), wherein PN is an integer of at least 2, and the superscript ‘a’ is a positive integer; (B) determining a difference DT(m,n) between the pixel (m,n) and the determined pixels on the row n−a by DT(m,n)=PN*f(m,n)−TOP a (m,n), and a difference DB(m,n) between the pixel (m,n) and the determined pixels on the row n+a by DB(m,n)=PN*f(m,n)−BOT a (m,n); (C) if |DT(m,n)|>|DB(m,n)|, providing an image difference DIF(m,n)=DT(m,n), otherwise, providing an image difference DIF(m,n)=DB(m,n); and (D) determining a temporary value T(m,n) of the pixel (m,n) by T(m,n)=(α*f(m,n)+DIF(m,n))/β for use as a new image value f′(m,n) of the pixel, where α is a positive enhancement factor and β is a positive division factor to make the value of T(m,n) range between 0 and a maximum gray-level.