A comparative, quantitative study of image compression techniques for use with digital particle image velocimetry has been performed. Several candidate compression algorithms were selected for the study, including a lossless technique and two mathematical transform-based methods. Each of the compression algorithms was implemented using commercial off-the-shelf software packages. Three image sequences were selected to exercise the various compression methods. These sequences included a set of industry standard images and two sets of images obtained from experimental work conducted at NASA Langley Research Center. Evaluation of the various methods was accomplished using quantitative perceptual and metrological performance measures. The results of the study indicate that several of the tested methods of compression are suitable for digital particle image velocimetry. A lossless LZ77 technique, coupled with pixel thresholding of image gray levels before compression, yielded excellent performance in terms of compression level and negligible introduction of spatial errors to the images. A lossy JPEG algorithm was shown to provide acceptable performance, however, significant spatial errors and increased numbers of false vectors derived from processing of the compressed images were observed at high compression levels. Finally, a lossy wavelet algorithm was shown to provide excellent performance in terms of minimal introduction of spatial errors and a reduction in the false vector rate over a wide range of compression levels. [References: 16]
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