High-Accuracy Digital Camera Color Transforms for Wide-Gamut Workflows

Metadata

Publisher: SMPTE — White Plains, NY, USA
Doc Type: Journal Article
Content Type: Original Research
Abbreviated Title: SMPTE Mot. Imag J.
Volume: 123, No. 8, pp. 33–40
Abstract: For digital camera systems, transforming from the native camera RGB signals into an intermediate working space is often required, with common examples involving transformations into the Academy Encoding Specification (ACES) or XYZ. For scene-linear camera signals, by far the most common approach utilizes 3 x 3 matrices (formed using regression methods), which are low-complexity approximations to the exact transformation that would be obtained using a full spectral analysis. For workflows designed for Rec. 709 displays, matrix-based input transforms are capable of producing reasonable accuracy in this domain. However, the 3 x 3 matrix colorimetric errors can become significant for saturated colors in workflows involving wide-gamut primary systems such as UHDTV or ACES. To address this shortfall, a novel input color transformation method has been developed that involves separate one-dimensional and two-dimensional operations. From the native camera RGB signals, chromaticity-like coordinates are computed, and these are used to index into a two-dimensional lookup table (LUT); the output of the two-dimensional LUT is then scaled according to the input signal. Because the surfaces associated with the two-dimensional LUTs possess many degrees of freedom, highly accurate colorimetric transformations can be achieved. For several cinematic and broadcast cameras tested, this new transformation method consistently shows a modest reduction of mean ΔE errors for colors within the Rec. 709 primaries. The improvement in accuracy becomes much more significant for saturated colors, for which the mean ΔE errors are reduced by more than a factor of three for colors that lie between Rec. 709 and Rec. 2020.
Publication Date: 2014-11-01
DOI: 10.5594/j18485
ISSN: Print: 1545-0279 | Electronic: 2160-2492
Link: https://doi.org/10.5594/j18485
Author(s): Jon S. McElvain
bio
Jon McElvain is a senior staff researcher with the Advanced Technology Group of Dolby Laboratories, and is based in Burbank, CA. He specializes in camera and display systems, image quality quantification, and image processing algorithm development. His previous positions were with Digital Imaging Systems GmbH, Micron Inc. (imaging division, now Aptina LLC) and with Xerox Corp. He has more than 20 publications and holds 25 patents. McElvain is a member of SMPTE and IS&T, and previously served as chair of the IEEE Standing Committee on Industry Signal Processing Technology (IDSP). He received a B.S. in physics from the University of California, San Diego, an M.A. in physics from the University of California, Berkeley, and a Ph.D. in physics from the University of California, Santa Barbara.
Walter Gish
bio
Walter Gish is principal member for Dolby's Image Technology Research and Development group, where he leads research and development efforts for next-generation imaging technology. He has more than 30 years of experience in signal and image processing, high-performance computing, and hardware development. He began his career working on classified sonar, radar, and image analysis applications for the U.S. government. Since the early 1980s, he has focused on computer graphics, video, and display technology. Before joining Dolby Laboratories Gish was principal engineer at Evans & Sutherland, executive scientist at Terabit, and chief technology officer at Interactive Machines, Inc. — Gish received screen credit for his work on The Last Starfighter, the first full-length motion picture to use extensive CGI. He received special recognition from ISO/IEC for his contributions to the development of the high profiles for H.264/AVC, which were awarded an Emmy in 2008. His current interests include compression algorithms, high-dynamic range, and wide color gamut imaging technology, and forensic watermarking.
Copyright: © 2014 Society of Motion Picture and Television Engineers, Inc.

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Jon S. McElvain and Walter Gish; High-Accuracy Digital Camera Color Transforms for Wide-Gamut Workflows, SMPTE Motion Imaging Journal ( Volume: 123, Issue: 8, November 2014); SMPTE, 2014. Available at https://doi.org/10.5594/j18485

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Jon S. McElvain and Walter Gish; High-Accuracy Digital Camera Color Transforms for Wide-Gamut Workflows, SMPTE Motion Imaging Journal ( Volume: 123, Issue: 8, November 2014); SMPTE, 2014. Available at https://doi.org/10.5594/j18485

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<span class="citation">Jon S. McElvain and Walter Gish; <cite>High-Accuracy Digital Camera Color Transforms for Wide-Gamut Workflows</cite>, SMPTE Motion Imaging Journal ( Volume: 123, Issue: 8, November 2014); SMPTE, 2014. Available at <a href="https://doi.org/10.5594/j18485" target="_blank" rel="noopener">https://doi.org/10.5594/j18485</a></span>

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Jon S. McElvain and Walter Gish; <cite id="bib-10-5594-j18485">High-Accuracy Digital Camera Color Transforms for Wide-Gamut Workflows</cite>, SMPTE Motion Imaging Journal ( Volume: 123, Issue: 8, November 2014); SMPTE, 2014
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