How can I accurately display the Sun’s ~5800 K color on a calibrated 6500 K monitor?
Asked 5/12/2012
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I’m processing a solar photo taken through a telescope with a dedicated white-light solar filter. My monitor is hardware-calibrated to about 6500 K, gamma 2.2, and 120 cd/m². I’d like the Sun to appear as close as possible to its natural color on that calibrated display.
Assuming I want to represent a roughly 5800 K blackbody on a 6500 K monitor, what RGB values should I aim for, and is there a practical workflow for doing this in software such as Lightroom or GIMP?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
11
The answer is: sRGB = (255, 241, 234).
The details of the calculation:
I calculated the spectrum of a blackbody at 5800 K using the Planck’s formula, then multiplied by the CIE color-matching functions of the standard 2 degrees observer and integrated over the wavelengths to get the (X, Y, Z) color. I then divided by X+Y+Z to get the chromaticity:
(x, y) = (0.3260, 0.3354)
multiplying (x, y, 1-x-y) by the XYZ to sRGB matrix, and dividing by the greatest component (R) yields:
(R, G, B) = (1, 0.8794, 0.8267)
I then gamma-encoded, multiplied by 255 and rounded to the nearest integer and got:
(R’, G’, B’) = (255, 241, 234)
Caveat: My answer is in the sRGB color space, which is almost, but not quite 6500 K with 2.2 gamma. BTW, “6500 K with 2.2 gamma” is not a color space specification: you also need the chromaticities of the primaries to get a fully-specified color space.
Originally by user1730. Source · Licensed CC BY-SA 4.0
user1730
14y ago
0
Generated from our catalog & community — verify before relying on it.
If you want an approximate display color for a 5800 K blackbody on a standard sRGB-like display, one community calculation gives:
- sRGB ≈ (255, 241, 234)
That was derived by converting a 5800 K blackbody spectrum through CIE XYZ, then into sRGB. In normalized linear RGB, it’s about:
- (1.000, 0.879, 0.827)
A few cautions matter here:
- Your monitor calibration target of “6500 K, gamma 2.2” is not, by itself, a full color-space definition.
- The answer above is specifically for sRGB, which is close to but not exactly the same thing.
- Your telescope filter, camera spectral response, possible IR leakage, atmospheric effects, and processing pipeline all affect the captured color.
- ICC/ICM color management should already help your software display colors correctly on a calibrated monitor.
So, in practice: use a color-managed workflow, and if you want a target visual reference for the Sun’s color, use approximately sRGB 255/241/234 as a reasonable guide. It should appear as a very slightly warm white rather than pure neutral white.
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