A system and method for detecting location and luminance transition range of slant image edge in a digital image. The variance value for the pixels inside a window in the image is calculated, based on which a current pixel is classified. If the current pixel is in a non-edge region, no further checking is needed, otherwise binary pattern data is generated from the pixels inside the window. Then it is determined whether the current pixel is a center pixel in a luminance transition range of a slant edge based on the binary pattern data at the current pixel location and its neighboring binary pattern data. If the current pixel is the center pixel in a luminance transition range of a slant edge, then the length of the luminance transition range of the slant edge is determined.