One of the essential mechanisms employed by the human visual system when interpreting the natural world is that of trichromatic integration of a physical scene spectrum by cone photoreceptors. By extension of this, different scene spectra can result in the same color sensation in an observer, a phenomenon known as metamerism which allows imaging systems to produce realistic reproductions of scene content by the same three channel simplification. To predict these matches, color matching functions are used which aim to describe the average spectral integration behavior of all observers. This practice has been shown to result in significant color rendering errors, however, as there exists a significant and natural variability in the spectral behavior of the optical pathway and photoreceptors within populations of color-normal observers. When this is crossed with the growing disparity between the spectral characteristics of emerging display technology it becomes evident that this inter-observer variability should be accounted for.
In lieu of more spectrally accurate imaging systems, a color management pipeline for motion picture production which considers the individual characteristics of key creative observers could remove this variability when color critical decisions are being made. For example, if for the various stages at which a Director of Photography reviews imagery (on-set, dailies, editing, color correction, vfx, mastering) their monitoring equipment is calibrated to be a metameric match to some reference considering their individual physiology, this would remove inconsistency relating to the differing display technology used and avoid any influence it may have on creative decisions. Additionally, it would allow an observer and display specific reference point to be established in the pipeline (for example, the colorist and primary mastering display) which imagery could be directly related to when remastering content for emerging formats.
Asano and Fairchild present a physiologically based individual observer model, as well as a method for separating a population of observers into a limited number of observer categories. Building on this work, an experiment is performed to show that observers can be reliably assigned to a category in a forced choice matching experiment involving natural images as stimuli. The results provide further evidence that inter-observer metameric variability is a relevant problem for motion picture production, and that categorical observer profiles can be a consistent and practical solution for removing this variability in the workflow. Then, various enhancements to standard color management workflows using critical observers' categorical functions are proposed.
Technical Depth of Presentation
As this involves cutting edge research, the technical depth of the presentation will be at least intermediate.
What Attendees will Benefit Most from this Presentation
Engineers who work directly on developing color pipelines for motion picture content production will find the most direct benefit from this information. However, technologists and engineers who work on color management in other regards (engineering camera/display pipelines) can also benefit from this information.
Take-Aways from this Presentation
- CIE standard observer color matching functions are insufficient to accurately produce a match for all observers between displays of different spectral quality.
- Visually detectable errors can be found by observers in natural images when a metameric match is predicted using color matching functions which are different from theirs own
- Categorical observer sets can be practically incorporated into color management pipelines