It also, of course, depends on what the goal is. Jeff, are you trying to figure out the CCT based on known multipliers, or trying to determine multipliers based on a known CCT, or … ? And, regardless, for what purpose? That is, once you know CCT / multipliers, then what? I ask because neither figure is likely to be especially useful in isolation. If the goal is to apply white balancing to an image, either number will get you in the ballpark and likely “close enough” for any casual usage — but neither will be “good enough” for color-critical work. I’ll also toss out there that, if you know a camera’s spectral response, you can, in theory, get a not-miserable spectral measurement of a scene’s illuminant from a photograph of a ColorChecker. You certainly won’t be able to identify Fraunhofer lines or anything like that; however, you should absolutely be able to determine the type of illuminant (actual daylight, incandescent, flash, fluorescent, etc.). And, for illuminants with variable spectra (especially daylight and incandescent), determining the precise color temperature (and thus exactly characterizing the spectrum) is also achievable. This should be extendable; you won’t get the precise spikes of a fluorescent source, but, if you know that the source is one of a known set to pick from, picking the right one should be trivial. I haven’t tried it, but, in principle, you should also be able to suss out ratios of mixed-lighting environments, too ... b&
On Dec 5, 2022, at 9:08 PM, Iliah Borg via colorsync-users <colorsync-users@lists.apple.com> wrote:
There is, Adobe DNG SDK suggests one way to approximate it, and there are other ways, too.
With Canon one can do interpolation as the raw files contain data like this:
10900, {2.92571f, 1.0f, 1.25183f, 1.0f}, 10000, {2.86034f, 1.0f, 1.28160f, 1.0f}, 8300, {2.70185f, 1.0f, 1.36533f, 1.0f}, 7000, {2.53465f, 1.0f, 1.46705f, 1.0f}, 6000, {2.36490f, 1.0f, 1.57538f, 1.0f}, 5600, {2.28062f, 1.0f, 1.63578f, 1.0f}, 5200, {2.18337f, 1.0f, 1.70383f, 1.0f}, 4700, {2.06452f, 1.0f, 1.81883f, 1.0f}, 4200, {1.92120f, 1.0f, 1.96923f, 1.0f}, 3800, {1.78397f, 1.0f, 2.11570f, 1.0f}, 3500, {1.67320f, 1.0f, 2.26549f, 1.0f}, 3200, {1.54683f, 1.0f, 2.45564f, 1.0f}, 3000, {1.46286f, 1.0f, 2.63239f, 1.0f}, 2800, {1.36533f, 1.0f, 2.79781f, 1.0f}, 2400, {1.16232f, 1.0f, 3.21003f, 1.0f}
On 12/5/22 23:00, Jeff Nova via colorsync-users wrote:
Just to be certain, it sounds like there is no possible route to CCT from these numbers, true? - J Jeff Nova Chief Executive Officer Colorhythm https://colorhythm.com Mobile: +1 510-710-9590 Main: +1 415-399-9921
-- Best regards, Iliah Borg LibRaw, LLC www.libraw.org www.rawdigger.com www.fastrawviewer.com _______________________________________________ Do not post admin requests to the list. They will be ignored. colorsync-users mailing list (colorsync-users@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/colorsync-users/ben%40trumpetpower.c...
This email sent to ben@trumpetpower.com