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; and generating an output image whose edge is detected so as to maintain the consistency of channel 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.