Why does my rainbow look different from yours?

[blekenbleu]

And yet the camera itself interprets this particular situation correctly -- the JPEG created in camera does not contain the dark band.

Camera's JPEG Yuv implementation could be tuned for its hardware artifacts.
Note that reviewers are often constrained to JPEG for preproduction cameras.

Perhaps this is just a simple bug in the profile.

As CrispyBee suggested, default commercial profiles are often tweaked for idiot-proof human skin tones.
Beyond that, general human color memory bias is a cultural thing,
and many diligent e.g. flower photographers learn to expect disappointment from commercial color [mis]management.

[rjlittlefield]

Adding to this thread some gory technical details that I would like to remember...

At https://www.cloudynights.com/topic/8660 ... ry12555752 , Lou Jost mentions that some nonlinear stretching was necessary to bring various representations into alignment.

I was intrigued to see that in my data, only linear operations were needed. The explanation is that for spectra from a diffraction grating, offset from the optical axis is linear in wavelength, per the formulas at https://en.wikipedia.org/wiki/Diffraction_grating#Theory_of_operation . So, it is only necessary to know the wavelengths of two points on the spectrum, and all other wavelength are simple to compute.

Here is an incredibly ugly montage of the spectrum collected by my Canon R7 (color band in the middle, lines intensified by strong USM filtering), overlaid on the annotated spectrum at https://upload.wikimedia.org/wikipedia/commons/7/7d/Fraunhofer_lines_DE.svg , also overlaid by the graph at https://upload.wikimedia.org/wikipedia/commons/e/e4/Solar_spectral_irradiance.svg , both linked from https://en.wikipedia.org/wiki/Fraunhofer_lines .



The pixel coordinates of certain major Fraunhofer lines (G,F,b1,E2,D2+D1,C) are pretty clear in my raw data. Working from the known wavelengths of those and the linearity of the spectroscope, I measured the actual wavelengths of my red and blue laser pointers. Those turned out to be blue = 407.2 nm (label says 405 +- 10) and red = 653.5 nm (label says 650 +-10). I assume these wavelengths will vary depending on environmental conditions, but I have no idea by how much or because of what conditions. If anybody knows these things, I would be interested in learning.

Edited to add... I see that I haven't shown any raw data for daylight. That looks like this:



--Rik