Abstract
The authors propose a method for reducing discontinuities between blocks (block distortions) caused by block processing in the enlargement (increase of pixel numbers) of a gray-scale digital image with an orthogonal transform. In the enlargement of a 1-dimensional signal series by transformation of the Fourier spectrum frequencies, the signal series within the block being processed is transformed based on the first signal value of the subsequent input block so as to connect the interpolation curves in the blocks at the block boundaries. The results of processing a test image demonstrated extremely small and hardly visible block distortions in images enlarged by the proposed method. In addition, block distortions were further reduced to the extent of becoming invisible, by implementing the proposed method with blocks overlapped at their sides. Even at a high enlargement ratio, for which conventional methods yielded substantially degraded images, interpolation by a high order curve resulted in smoothing between pixels and yielded enlarged images that were comparatively less blurred. Based on these results, the authors discuss the issues of block length and the proper overlap value. In addition, when the fast Fourier transform was used, the processing time was of the same order as, or lower than, that obtained in conventional interpolation methods. © 1998 Scripta Technica, Syst Comp Jpn, 29(8): 38–47, 1998
Published Version
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