Appealing to color science is a reliable approach to alienating associates, customers, and jurists; you’re telling them they can’t trust their own eyes.

The damnable problem is that this claim is absolutely true and is endorsed by psychologists, optometrists, color scientists, etc.

Visual photonic, physiologic, and psychologic processes are shockingly complex, as is digital imaging science (our industrial generation of visual experiences). This tends to discourage engagement.

One of the most potent demonstrations of the problematic use of color exists in the discipline of thermography, that is the use of cameras sensitive to infrared rather than visible band electromagnetic energy. That invisible energy must be translated to visible band artifacts for humans to view, and that translation is mathematically and cognitively perilous.

Comparison of Thermal Palette Mapping: Viridis v. Ironbow
Comparison of Thermal Palette Mapping: “Viridis” v. “Ironbow.”

The preceding diagram illustrates the differences between two color mapping schemes. The top red, green, and blue channel graphs are a forensically defensible color mapping schema that is perceptually uniform and “robust to colorblindness.” Perceptual uniformity is critical in qualitative visual assays.

The bottom three channel graphs are a common color mapping schema for thermography, “Ironbow.” Note that the color mapping is radically different between the two procedures.

It is reasonable to ask, “so what?”

The most direct answer is to explain that color error in human vision is common; not necessarily complete “color blindness” (achromatopsia), but assorted versions and magnitudes of variable color sensitivities. Two of these dyschromatopsias are so relevant in the imaging and graphics worlds that Photoshop maintains a top-level menu item for “proofing” output germane to them.

Ironbow Palette re Protanopia and Deuteranopia
“Ironbow” Palette (Left) and as Viewed by an Exemplar Protanope and Deuteranope. The Protanope Will Perceive Higher Contrast and the Deuteranope Lower Contrast in Areas of Relevant Detail.

Another relevant concern is that while digital imaging is formulated upon a trichromatic theory (red, green, and blue), human vision is not.

Visual Opponent Color Process Graphic
Visual Opponent Color Process Graphic.

The common model of human vision is predicated upon an “Opponent Color Process” that is functionally distinguishable from the classic trichromatic theory; the above graphic exhibits an obvious juxtaposition of red v. blue, and green v. yellow. This diversity is not without material consequences in the digital and computer science realms.

Spatial and temporal parameters are just as complex as colorimetric concerns. If you’d like to test those waters buy a book on “The Visual Process” and look into Receptive Fields, Lateral Inhibition, and Phototransduction.

Comparison of Thermal Palette Mapping: Glowbow v. Grayscale
Comparison of Thermal Palette Mapping: “Glowbow” v. “Grayscale.”

A grayscale palette may be considered somewhat more objective than an aggressively colored palette but has its own insufficiencies. The preceding diagram illustrates the differences between two additional color mapping schemes; the top red, green, and blue channel graphs are another common color mapping schema for thermography, “Glowbow.”┬áThe bottom three channel graphs are the common grayscale mapping schema for thermography, “Grayscale,” with a “white = hot” distribution.

Comparison of Thermal Palette Mapping: Viridis v. Grayscale
Comparison of Thermal Palette Mapping: “Viridis” v. “Grayscale.”

Comparing the grayscale to the perceptually uniform standard (above) illustrates why simply linear solutions aren’t necessarily a therapy; the mapping differences between the two schemes are quite obvious.

This also begs a question concerning human visual acuity; humans are able to discern perhaps 200 levels of grayscale, somewhat shy of the 256 levels mathematically specified by the 8-bit image file standard and without a terribly strong correlation to any particular monitor performance or operation, particularly in non-color managed environments.

Beneath these concerns lie very real image compression concerns and uncertainties of assured visual acuity for triers of fact.

Color in thermography is problematic.

Ironbow Palette re Grayscale and Viridis
Comparison of Thermal Palette Mapping: “Ironbow” v. “Grayscale” v. “Viridis” (Perceptually Uniform).

In the above graphic details in the lower right quadrant of the frame are mitigated in “Ironbow” but well-defined in the “Grayscale” and “Viridis” treatments. The details (not the color) of the “Grayscale” and “Viridis” treatments should be virtually indistinguishable to observers with relatively standard vision.

L

Author

Expertise: Defensible extreme-specification forensic and research LiDAR (LASER Scanning) and thermographics, near-infrared & visible band imagery (photography, videography, time lapse, macro- and microphotography & video). Environmental controversies including water temperatures, geotechnics, and erosion volumetrics, architectural illumination. Construction, engineering, and craning operations and incidents. Color management, color science, and human visual acuity relevant to litigation. Certified Level II (Advanced) and Level III (Master, Managerial) Thermographer; FLIR Infrared Training Center. Certified Terrestrial LiDAR operator; theory, planning, and data interpretation; FARO Technologies, GmbH. Certified Aerial Photographer (Professional Aerial Photographers Association, International). Certified Master Aerial Photographer (Professional Aerial Photographers Association, International: one of ~50 to ever receive the award as of 7/18). OSHA 30 Certified (General Industry). Adobe Certified Expert: Photoshop (CS4, CS5, CS6, CC). Adobe Certified Expert: Premiere Pro (CS6, CC). Adobe Certified Expert: Flash Professional (CS5, CS6, CC). Adobe Certified Expert: Web Specialist (CS6). Adobe Certified Expert: Video Specialist (CS6, CC; 1 of 105 in the world as of 7/18). (Inactive) Member, Professional Advisory Board, Stevens-Henager College. (Inactive) Moderator for Adobe's online Photoshop, Premiere, & Flash forums. (Inactive) Lecturer, Law Seminars International.

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