Effects of Chromatic Aberration Compensation on Visibility of Compression Artifacts. Mohona, S. S., Au, D., Hou, Y., Kio, O. G., Goel, J., Jacobson, N., Allison, R. S., & Wilcox, L. M. In CVR/VISTA Virtual Vision Futures Conference, pages 48. Toronto, Canada, 06, 2021.
Effects of Chromatic Aberration Compensation on Visibility of Compression Artifacts [pdf]Paper  Effects of Chromatic Aberration Compensation on Visibility of Compression Artifacts [pdf]-1  abstract   bibtex   
In virtual and augmented reality displays, lenses focus the near-eye display at a far optical distance and produce a large field of view to immerse the user. These lenses typically exhibit considerable distortion and cause chromatic aberration. These are not apparent to the user because they are typically corrected by pre-processing the image with the opposite distortion before sending it to the display. Such pre-processing involves pre-warping source images with inverse pin-cushion (barrel) distortion to correct for the pin-cushion transform from the display optics with different correction for each colour channel. Most image compression algorithms use a colour space conversion before compression which normally improves compression performance by reducing the degree of correlation between components. However, as lens pre-distortion processing is colour specific the spatial correlation between colour channels is disrupted by this processing; objective analyses suggest that the colour space conversion may not be beneficial under these conditions. Here we used the ISO/IEC 29170-2 flicker protocol that has been adapted for 3D imagery, to evaluate the sensitivity of two state- of-the-art display stream compression algorithms to characteristic distortions resulting from stereoscopic head-mounted display pre-processing which either included normal colour transformations or bypassed them. A set of 10 computer-generated stereoscopic high dynamic range images were tested. Images spanned a wide range of content and were designed to challenge the codecs. The pre-processing workflow involved pre-warping the images, compressing with each codec, and finally de-warping with pin-cushion distortion. De-warping was applied to simulate the distortion from magnifying lenses as all images were viewed on a mirror stereoscope without such lenses. The main image manipulations were the codec used, the compression levels and whether the colour transform was bypassed (bypass-on) or not (bypass-off). Images were compressed at the codec's respective nominal production level and at each image's estimated limit of visually lossless compression. 60 observers were tested in 3 groups of 10 for both codecs. Overall, we found little sensitivity to these distortions and our results confirmed that bypassing colour transforms in the codec can be significantly beneficial for some images.

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