180° rotation of digital images with concurrent compression

Abstract

A method of rotating an input image matrix of pixel data 180° to form an output image matrix of pixel data using a computer. The input image matrix is divided into pre-rotated bands of image pixels. Groups of pixels of a first pre-rotated band are accessed beginning at a bottom end of the first band and ending at a top end of the first band. The order of the pixels within each group of pixels of the first band is then reversed. The groups of reordered pixels are written to a band memory to form a rotated band of pixel data. In the rotated band of pixel data, the order of the groups of pixels of the rotated band is in reverse order to the order of the groups of pixels in the first band. The steps of accessing, reversing, and writing steps are repeated for the other bands of image pixels. Finally, the rotated bands are combined in reverse order of the pre-rotated bands to form the output image matrix. Optionally, the bands are concurrently reordered and compressed. By appropriately selecting the size of the groups of pixels and performing the steps on separate direct memory access masters, the method can take advantage of the bandwidth of high-performance busses to rotate and compress data in real-time.

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