1. An image filtering method, comprising: receiving an original image; generating a plurality of first images by filtering the original image with filters respectively generated along a plurality of channels; generating a second image by selecting a channel having a maximum value for each image unit, from the generated first images wherein the image unit represents a basic unit in operation of an image; and generating an output image whose edge is detected by filtering the second image with filters respectively generated along the plurality of channels to generate a plurality of third images and comparing the channel of the second image with the channels of the third images.