Approximating color temperature with smart phones and camera

I know this is old, but I’ll add that the $170USD XRite Colormunki is supposed to be about as accurate a display calibrator as the Pro. We bought it few years ago for SO’s photography business, as any digital graphic artist is working blind if their displays aren’t calibrated.

I leave my own displays uncalibrated, though. For general use, the factory calibration is often more pleasing than accuracy. Just don’t imagine your images will look the same on all devices, or print accurately. Or render beamshot tints especially accurately. And I don’t even bother to print images I’ve taken, because I know only images like hers, shot in Raw and edited on a calibrated monitor, will print similarly to how they appear on the screen.

So I think the ColorMunki Photo + Argyll will give full spectral data and would be the least costly solution.

So CCT, CRI, DUV, etc right since it’s a spectrophotometer and not simply a colorimeter. Is this right?

Yes, you’re correct. Also goes for the new i1Studio.

Wicked!

I’ve got the i1 so this is definitely something I’m going to be checking out, great stuff as always maukka!

I ordered a used one from eBay for $250, will play around with it and report back!

ColorMunki Photo arrived.

I got the Argyll drivers installed and began with “spotread -a” after reading only a fraction of the documentation.

I hope maukka can provide a crash course tutorial for me/us. Some initial questions:

  • Should I be concerned about distance from my light to meter?
  • How much do I care about ambient light? My room is fairly dark and I put the device under my desk w/ monitor on and shine light from desktop height?
  • What spotread command works best for our flashlights?
  • What is it doing during calibration? Do I need to have it set up any special way?
  • It said (Caution) in the output on some lights/modes but still gave me somewhat reasonable output. Should I be concerned?
  • Continued from above, will I run into a lux ceiling and how can I adjust to measure higher output if so?

Any other best practices would be appreciated. For a ~$250 outlay if I can get my dual monitor setup calibrated at work (same model monitor but different panels and ~5 years apart) and still use it to screw around with LEDs seems like a pretty “fun” investment.








219C 4000K 90CRI w/ smooth narrow carclo @ high-ish amps, measured from about 2.5 feet away:

Luxeon MZ 3000K + 5700K in Cute4 medium optic:

Medium output:

High ~12A output:

  • Should I be concerned about distance from my light to meter?

Because the meter also works as a lux meter, if you want to measure cd you need to know the distance to convert from lux (cd = lux*(distance in meter)^2, throw in meters = square root(cd/0.25))

  • How much do I care about ambient light? My room is fairly dark and I put the device under my desk w/ monitor on and shine light from desktop height?

Ambient light is usually so minuscule in intensity in relation to the light you’re measuring that it usually has no effect on the results.

  • What spotread command works best for our flashlights?

Looking at the printout it seems you got that already figured out, I’d just add -H for hires mode and -x for xy coordinates in the CIE space :+1:

  • What is it doing during calibration? Do I need to have it set up any special way?

It calibrates for dark reading. No need to do anything else than put the device in calibration mode (rotate the side wheel to the correct orientation)

  • It said (Caution) in the output on some lights/modes but still gave me somewhat reasonable output. Should I be concerned?

The measurement might have been clipped at some wavelengths which could skew the results.

  • Continued from above, will I run into a lux ceiling and how can I adjust to measure higher output if so?

Increase distance.

  • Any other best practices would be appreciated. For a ~$250 outlay if I can get my dual monitor setup calibrated at work (same model monitor but different panels and ~5 years apart) and still use it to screw around with LEDs seems like a pretty “fun” investment.

It’s as simple as that. And fun!

Thanks for all the responses. I will try to refine my testing a bit to make sure everything is consistent. I did test the calibration at work and it got my 2 displays calibrated closer to each other in 10 minutes than I could achieve with publicly uploaded ICC profiles and manual adjustments after hours. Looks to be a very versatile device.

I have a USB on the go cable I will try with an android tablet and ArgyllPro ColorMeter DEMO version as well as BabelColor evaluation copy. Are there any open source or free/cheap things to try? Argyll’s command line tools seem pretty full featured but they don’t show the same eye candy of your BabelColor screen captures!

HCFR is free and it can plot the xy coordinates and show a colorful spectrum image.

I thought i read somewhere you could make your own spectrum image with the XY data, can you elaborate? Maybe i can just make my own program to read .sp output and plot exactly what i need

You can graph the spectrum in Excel for example, but not using the CIExy data. That’s just the tint coordinate. Spotread -s gives you the necessary wavelength data for that. Or plots the spectrum with -S.

Is there any way of knowing how accurate the Aperture Meter Android app is?

It has a calibration feature for CCT and lux so it could work. I’ll have to check it out.

edit: did some tests, on my phone (the ancient Motorola Moto E) the CCT reading doesn’t work since the phone doesn’t have an RGB front light sensor and its lux readings are all over the place and wildly vary with different CCT and CRI sources. So, may or may not work depending on the device.

I see the spectral data in the file but how do you go from that to this? or maybe I just need this to be written to the file so I can parse it?

Yxy: 7578.662723 0.364250 0.361470


Ambient = 7578.7 Lux, CCT = 4375K (Duv –0.0022)


Color Rendering Index (Ra) = 89.9 [ R9 = 77.8 ]

R1 = 92.2 R2 = 90.6 R3 = 87.2 R4 = 90.1 R5 = 91.2 R6 = 86.0 R7 = 91.1
R8 = 91.0 R9 = 77.8 R10 = 77.0 R11 = 90.9 R12 = 73.9 R13 = 91.1 R14 = 92.8

Trying to do something like you do here:

That’s just a spreadsheet plotting those xy coordinates.

edit: you could also check out Osram Color Calculator.

but i only see those coordinates in the spotread output not in the spectrum file it saves

I usually just take a single measurement and log the data by piping the output to a file, because spotread doesn’t save all the data in the log. Or just copy and paste the text from the command line window. After first calibrating, use whatever parameters and -N -O > log.txt

Is it likely that the accuracy is device dependent?

This free program Osram ColorCalculator is super cool. I re-arranged the spectrum data into a CSV and imported it:

Here is a SST-20 3000K on high with a frosted optic

CIE plot:

R-value plot:

Some report like babel shows:

The actual program window:

Can somebody tell me how to calibrate the colors on a projector connected to one of those stupid fruit-branded all-in-one desktop computers? At our church, the media computer is a Mac of some sort, a few years old. The projector is connected by HDMI over Thunderbolt, IIRC. The colors are horrible! Blues are over-saturated while reds are badly washed-out. I tried the on-board “monitor calibration” …thing on the Mac, but it only had brightness, contrast, maybe gamma, but no per-color-channel fixing. The projector itself has per-color-channel controls, but they don’t help, so the problem seems to be in the signal from the Mac! The LCD monitors connected to the Mac show colors “fine” though. Just the projector doesn’t. So, I don’t know what the deal is actually. Help?