Patent ID: 8285036

Claim:
An image processing method for extracting an edge from a color image comprising pixels each of which expressed by color component values of three R, G, and B colors, comprising: calculating a lightness value of each of the pixels based on the color component values of three colors corresponding to said each of the pixels; determining which one of the low, medium, and high lightness regions defined by dividing a predetermined lightness range into three the lightness value thus calculated belongs to; generating an extraction image comprising pixels corresponding to said each of the pixels of the color image; wherein, for a pixel of which the lightness value belongs to the medium lightness region, a pixel value is determined based on the color component values of three colors, wherein, for a pixel of which the lightness value belongs to the low lightness region, a pixel value is determined based on the color component values excluding at least one of the color component values of three colors; and wherein, for a pixel of which the lightness value belongs to the high lightness region, a pixel value is determined based on the color component values of two colors of the color component values of three colors, or, based on the lightness value and the color component value of B; and extracting an edge based on the pixel value of the extraction image thus generated.