Method and apparatus for rotating a digital image ninety degrees

Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel

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382297, 345201, G09G 500

Patent

active

055981810

ABSTRACT:
A method for rotating an image clockwise or counter clockwise by ninety degrees in place in an image buffer with a small auxiliary buffer is disclosed. The image, defined by a rectangular pattern of H lines with each line having W pixels, is segmented into square blocks of N pixels per row and N lines per column. The image is stored in an image buffer, and each square block of pixels in the image buffer is rotated by ninety degrees. A starting memory location in the image buffer is selected from a set of starting memory locations, and a memory word at the selected starting memory location is copied into a memory word of a temporary storage buffer. A replacement memory location in the image buffer is determined for the memory word in the temporary storage buffer, which is swapped with a memory word at the replacement memory location. A sequence of replacement memory locations is defined by repeating the preceding operation until the selected starting memory location in the image buffer is determined to be a replacement memory location in the image buffer for the memory word in the temporary storage buffer. The sequence of replacement memory locations is terminated by replacing the memory word at the selected starting memory location with the memory word in the temporary storage buffer.

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