Faster lossless rotation of JPEG images
First Claim
1. A method of lossless image rotation by operation on compressed data including steps of associating an R value of a run length of zero-values preceding a non-zero orthogonal transformation coefficient in a zig-zag order with an S value corresponding to an adjacent, following, non-zero orthogonal transformation coefficient in a reverse zig-zag order in a matrix of orthogonal transformation coefficient, and outputting said R value and said S value with said orthogonal transformation coefficient.
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Abstract
Image rotations of 90°, 180° and 270° and horizontal and vertical mirroring image transformations are performed losslessly and with greatly enhanced speed by processing orthogonal transform coefficients in a zig-zag order with direct storage of S (size) values, reassociated R (run of zero valued coefficients) from an adjacent coded orthogonal transform value and a non-zero valued transformation coefficient in reverse zig-zag order. Cache misses are avoided by processing values which are not widely separated in the coded data and other features of the technique and memory accesses are reduced to accelerate processing while extremely little computation is required. These effects are substantially augmented when intermediate codes having certain attributes including coding of zero valued coefficients and flagging certain code features are employed.
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Citations
22 Claims
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1. A method of lossless image rotation by operation on compressed data including steps of
associating an R value of a run length of zero-values preceding a non-zero orthogonal transformation coefficient in a zig-zag order with an S value corresponding to an adjacent, following, non-zero orthogonal transformation coefficient in a reverse zig-zag order in a matrix of orthogonal transformation coefficient, and outputting said R value and said S value with said orthogonal transformation coefficient.
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12. A method of performing lossless rotations of image data including the steps of
rearranging or maintaining orthogonal transform coefficient zig-zag order, depending on rotation angle, altering signs of said orthogonal transform coefficients by an exclusive OR operation inverting binary values of said orthogonal transform coefficients, and storing an R value with an adjacent S value and orthogonal transform coefficient value in reverse zig-zag order if said zig-zag order is rearranged.
Specification