EOS R8: Custom White Balance - Kelvin value?

[justadude]

This is a bit of an off the wall question concerning custom white balance that I'm 99% sure I will not get an answer on, but here goes.  When I set a custom WB and take a photo, is there a way to find a Kelvin value to it in the file?

Let me explain why I am asking...

I am shooting infrared with a full spectrum Canon R8.  When I set a custom white balance I put a 720 nanometer lens filter on the camera, then to set it I make sure the camera is pointing towards green sunlit foliage.  Now if I want to shoot in the 850nm spectrum, I put that filter on, and repeat the custom WB setup steps.  I do this with 5 different wavelength filters each time I change from one to the other.  Sounds like a pain in the... foot.  However after 25 years of doing this it is second nature for my infrared photography.

I've done this with various Kodak, Pentax and Canon cameras over the years.  Never had a problem with getting a nice custom WB... until the R8.  I can nail 4 of the 5 wavelengths each time I set a custom WB, with the exception of the 720nm.  I have no idea why this one is hit or miss on this particular camera, and only at this wavelength, but never on any other wavelength or other camera (including any of my other Canon cameras).

So my thoughts are IF there is a way to determine a Kelvin value of a file (or any other way to tell the temperature that I'm not thinking of), maybe on the rare times that I hit the correct custom value, I could look it up, then set Kelvin values from that point on.

Also, to my knowledge, if I save settings as a Custom Program setting on the menu, it won't keep the WB in the Custom menu once I change the custom WB for a different wavelength.  At least that was my experience with other cameras.

[rs-eos]

Not that I know of. Though beyond the ºK value, a custom white balance could also vary the tint.

It's possible you could do something with trial and error, but with two variables in play, that may get way too tedious.

[shadowsports]

Greetings,

I just dove into this and came to the same conclusion as Ricky.  I did find a white balance setting on the recipes tab of a cr3 image in DPP, but found no way of displaying actual Kelvin temp after setting a Custom White Balance.  

This is not available on the R8 (either) as far as I can tell

[johnrmoyer]

Exiftool will report some of the color temperature values recorded by the camera. The color temperature in the camera seems to me more complicated than a single Kelvin number. It seems to me likely that it is calculated from the RGGB numbers measured when the shot is made and modified by by the RGGB values recorded when the custom white balance image was made.

Here is an example using a custom white balance file followed by setting the white balance to 5600K using the camera menu. My camera is EOS R5, but I expect yours to be similar.

exiftool -s -G0:2 -filename -"*whitebalance*" -"*RGGB*" -"*_WB*" -colortempkelvin -h /Volumes/EOS_DIGITAL/DCIM/100CANON/IMG_3642.CR3

File:Other	FileName	IMG_3642.CR3
MakerNotes:Image	WhiteBalance	Custom
MakerNotes:Image	WhiteBalanceRed	0
MakerNotes:Image	WhiteBalanceBlue	0
MakerNotes:Camera	MeasuredRGGB	473 1024 1024 414
MakerNotes:Camera	WB_RGGBLevelsAsShot	2250 1024 1024 1745
MakerNotes:Camera	WB_RGGBLevelsAuto	2144 1024 1024 2131
MakerNotes:Camera	WB_RGGBLevelsMeasured	2144 1024 1024 2131
MakerNotes:Camera	WB_RGGBLevelsDaylight	1975 1024 1024 1886
MakerNotes:Camera	WB_RGGBLevelsShade	2305 1024 1024 1613
MakerNotes:Camera	WB_RGGBLevelsCloudy	2131 1024 1024 1753
MakerNotes:Camera	WB_RGGBLevelsTungsten	1369 1024 1024 2929
MakerNotes:Camera	WB_RGGBLevelsFluorescent	1689 1024 1024 2796
MakerNotes:Camera	WB_RGGBLevelsKelvin	1975 1024 1024 1886
MakerNotes:Camera	WB_RGGBLevelsFlash	2212 1024 1024 1683
Composite:Camera	WB_RGGBLevels	2250 1024 1024 1745
MakerNotes:Camera	ColorTempKelvin	5200
File:Other	FileName	IMG_3643.CR3
MakerNotes:Image	WhiteBalance	Manual Temperature (Kelvin)
MakerNotes:Image	WhiteBalanceRed	0
MakerNotes:Image	WhiteBalanceBlue	0
MakerNotes:Camera	MeasuredRGGB	475 1024 1024 406
MakerNotes:Camera	WB_RGGBLevelsAsShot	2056 1024 1024 1814
MakerNotes:Camera	WB_RGGBLevelsAuto	2185 1024 1024 2056
MakerNotes:Camera	WB_RGGBLevelsMeasured	2185 1024 1024 2056
MakerNotes:Camera	WB_RGGBLevelsDaylight	1975 1024 1024 1886
MakerNotes:Camera	WB_RGGBLevelsShade	2305 1024 1024 1613
MakerNotes:Camera	WB_RGGBLevelsCloudy	2131 1024 1024 1753
MakerNotes:Camera	WB_RGGBLevelsTungsten	1369 1024 1024 2929
MakerNotes:Camera	WB_RGGBLevelsFluorescent	1689 1024 1024 2796
MakerNotes:Camera	WB_RGGBLevelsKelvin	2056 1024 1024 1814
MakerNotes:Camera	WB_RGGBLevelsFlash	2212 1024 1024 1683
Composite:Camera	WB_RGGBLevels	2056 1024 1024 1814
MakerNotes:Camera	ColorTempKelvin	5600

[johnrmoyer]

---

@rs-eos wrote:

Not that I know of. Though beyond the ºK value, a custom white balance could also vary the tint.

It's possible you could do something with trial and error, but with two variables in play, that may get way too tedious.

---

You are correct that it is more complicated than a single Kelvin number.

Exiftool will calculate RedBalance and BlueBalance from the WB_RGGBLevels associated with the chosen white balance. I have not looked at how the calculation is done. If one selects "Daylight" WB, then it appears to be that the Kelvin value will always be 5200. If one selects "Auto WB" then it appears to me that the reported Kelvin value is not meaningful.

[shadowsports]

Nice work John.  I was looking at the graph that represents CWB.  Nice that ExifTool does the calculation, but in a simplistic manner.  The K* mapping just isn't there.  

[Waddizzle]

I usually shoot RAW and dial in a color temperature when shooting in sunlight. I use Auto WB White Priority under artificial lighting. 

I use Adobe LR, but I am on my phone with no access to it until later tonight. But I believe that you can adjust the color temperature and tint using sliders, provided that you shoot RAW. 

[johnrmoyer]

For green ( e.g. foliage ), color temperature in Kelvin is not likely to be useful by itself.

https://en.wikipedia.org/wiki/Color_temperature

From the author of exiftool:

January 05, 2023, 07:12:59 PM

I'm guessing that you could use the ExifTool Composite RedBalance and BlueBalance tags for the red and blue in the DNG.  These are just R/G and B/G from the WB_RGGB values.

- Phil

"

Although the concept of correlated color temperature extends the definition to any visible light, the color temperature of a green or a purple light rarely is useful information.

"

In Canon DPP software: https://cam.start.canon/en/S002/manual/html/UG-04_EditImage_0040.html#EditImage_0050_7 there is 2 dimensional adjustment. Kelvin adjusts blue to amber as one dimension and the other dimension is green to magenta.

[justadude]

I have done a ridiculous amount of trial and error over the past year before deciding to check here in the forum.  Thanks, Ricky.

[justadude]

Thanks, John.  There is a lot of good information there, but I don't think there would be a way to apply all off that in the settings for upcoming shots.