The Channel Blur effect blurs a clip’s red, green, blue, or alpha channels individually. You can specify that the blur is horizontal, vertical, or both.

Select Repeat Edge Pixels to make the blur algorithm operate as if the pixel values beyond the edge of the clip are the same as those of the edge pixels. This option keeps edges sharp, preventing the edges from darkening and becoming more transparent—the result of being averaged with a lot of zeroes. Deselect this option to make the blur algorithm operate as if the pixel values beyond the edge of the clip are zero.