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Abstract. With the advent of modern computing and imaging technologies, digital holography is becoming widespread in various scientific disciplines such as microscopy, interferometry, surface shape measurements, vibration analysis, data encoding, and certification. Therefore, designing an efficient data representation technology is of particular importance. Off-axis holograms have very different signal properties with respect to regular imagery, because they represent a recorded interference pattern with its energy biased toward the high-frequency bands. This causes traditional images' coders, which assume an underlying 1∕f 2 power spectral density distribution, to perform suboptimally for this type of imagery. We propose a JPEG 2000-based codec framework that provides a generic architecture suitable for the compression of many types of off-axis holograms. This framework has a JPEG 2000 codec at its core, extended with (1) fully arbitrary wavelet decomposition styles and (2) directional wavelet transforms. Using this codec, we report significant improvements in coding performance for off-axis holography relative to the conventional JPEG 2000 standard, with Bjøntegaard delta-peak signal-to-noise ratio improvements ranging from 1.3 to 11.6 dB for lossy compression in the 0.125 to 2.00 bpp range and bit-rate reductions of up to 1.6 bpp for lossless compression.

Abstract-This paper reports results of subjective and objective quality assessments of responses to a grand challenge on light field image compression. The goal of the challenge was to collect and evaluate new compression algorithms for light field images. In total seven proposals were received, out of which five were accepted for further evaluations. For objective evaluations, conventional metrics were used, whereas the double stimulus continuous quality scale method was selected to perform subjective assessments. Results show competitive performance among submitted proposals. However, in low bitrates, one proposal outperforms the others.

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Recently several papers reported efficient techniques to compress digital holograms. Typically, the rate-distortion performance of these solutions was evaluated by means of objective metrics such as Peak Signal-to-Noise Ratio (PSNR) or the Structural Similarity Index Measure (SSIM) by either evaluating the quality of the decoded hologram or the reconstructed compressed hologram. Seen the specific nature of holograms, it is relevant to question to what extend these metrics provide information on the effective visual quality of the reconstructed hologram. Given that today no holographic display technology is available that would allow for a proper subjective evaluation experiment, we propose in this paper a methodology that is based on assessing the quality of a reconstructed compressed hologram on a regular 2D display. In parallel, we also evaluate several coding engines, namely JPEG configured with the default perceptual quantization tables and with uniform quantization tables, JPEG 2000, JPEG 2000 extended with arbitrary packet decompositions and direction-adaptive filters and H.265/HEVC configured in intra-frame mode. The experimental results indicate that the perceived visual quality and the objective measures are well correlated. Moreover, also the superiority of the HEVC and the extended JPEG 2000 coding engines was confirmed, particularly at lower bitrates.

A 3D extension of the standard will support cuboid volumetric data sets with no time component. Medical and scientific imaging equipment generate a significant amount of volumetric data. Because such data sets tend to be very large, powerful compression technology is crucial for efficient storage and transmission, random access, region of interest (ROI) support, and resolution/quality scalability. JPEG2000, the current standard devised by the Joint Photographic Expert Group (JPEG), provides this functionality for 2D data sets through Part 1 (Core Coding Systems) 1 and Part 2 (Extensions). 2 Although the latter indirectly supports a 3D wavelet transform by means of the extended multiple component transform, a complete volumetric coding scheme is still essential to functionality, optimal rate-distortion performance, and isotropic behavior for all dimensions.

Significant research efforts have been invested in attempting to reliably capture and visualize holograms since their inception in 1962. However, less attention has been given to the efficient digital representation of the recorded holograms, which differ considerably from digitally recorded photographs. This paper examines the properties of recorded off-axis holograms and attempts to find a suitable sparse representation for holographic data. Results show significantly improved Bjøntegaard delta PSNR up to 5 dB on average within a bit-rate range of 0.125 to 2 bpp when combining the direction-adaptive discrete wavelet transform with non-standard decomposition schemes for microscopic off-axis holographic recordings; up to 7.5% reduction of file size has been achieved in the lossless case.

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