Efficient implementation of mirror-mode edge handling in image filtering

A method of image filtering, the method comprising:

• storing in line buffers image data corresponding to a plurality of rows of an image, wherein the line buffers include N lines, where N is an integer and each line of the line buffers stores a row of image data from the image, wherein lines 0 to N−1 of the line buffers respectively store data of rows M−N to M−1 of the image data, where M is an integer that represents the number of rows of data in the image data;
• defining filtering coefficients of a filter, wherein a filtering coefficient c(n) is a filtering coefficient for row n of the filter, where n is an integer that represents a row number of the filter, wherein when row numbers of the filter are numbered 0 to N−1, c(n) is equal to 0 when n is less than 0 or when n is equal to or greater than N;
• and
• determining, for each line k of the line buffers, which filtering coefficient or coefficients apply, wherein k is an integer that represents a line number in the line buffers, further wherein when lines numbers of the line buffers are numbered from 0 to N−1, k is equal to or greater than 0 and less than N;
• wherein for each line k of the line buffers, filtering coefficients c(k−x)+c(2N−x−1−k) apply, where x is a positive integer that indicates by how many rows the filter is below the image, and wherein the defining and the determining are performed by one or more processors.

A non-transitory computer-readable medium including sequences of instructions, the sequences of instructions including instructions which when executed cause a computer to perform:

• storing in line buffers image data corresponding to a plurality of rows of an image;
• filtering image data on one row of the plurality of rows;
• and
• filtering image data on another row of the plurality of rows without changing the image data stored in the line buffers between filtering image data on the one row and filtering image data on the another row.