A method for generating an all-in-focus image is provided. In the method, a plurality of frames including one source frame and several reference frames captured at different focus lengths are obtained. After performing a motion compensation procedure on the frames, for each pixel position belonging to an edge, a characteristic similarity between the source frame and each reference frame is calculated respectively to accordingly select a plurality of qualified reference frames among the reference frames. The method further includes determining a first type color space component of the pixel position within an all-in-focus image by an edge sharpness corresponding to the pixel position within each of the source frame and the qualified reference frames, and determining a second type color space component of the pixel position within the all-in-focus image by an color brightness corresponding to the pixel position within each of the source frame and the qualified reference frames.