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Author Topic: White Balance and Photoshop's Tint Slider Calibration  (Read 3885 times)

xpatUSA

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White Balance and Photoshop's Tint Slider Calibration
« on: May 30, 2014, 10:33:04 am »

I'm researching something which is outside of the standard methods for setting the white balance for a scene relative to it's illumination. I shoot raw. As part of that research, I want to set the WB in PhotoShop Elements ACR 5.4 to emulate the CIE illuminant 'E'. The CCT is easy enough - 5455K according to WikiPedia, but what about the tint setting? As we know, illuminant E lies below the Planckian line on the CIE 1931 chromaticity chart, so I assume the tint setting should be +n but what is n for illuminant 'E'? In other words, how do Adobe's tint values relate to the CIE chart (xyY or Luv, either one) ?

Thanks,
« Last Edit: May 30, 2014, 01:12:14 pm by xpatUSA »
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digitaldog

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #1 on: May 30, 2014, 11:29:04 am »

I doubt a CCT Kelvin value will fly and even if it did, it will probably be interpreted differently based on the converter, camera profile and a lot of other factors.
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xpatUSA

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #2 on: May 30, 2014, 11:55:29 am »

I doubt a CCT Kelvin value will fly and even if it did, it will probably be interpreted differently based on the converter, camera profile and a lot of other factors.

Thank you, Richard Andrew (sorry, 3 June).

Do you happen to know the relationship between the Adobe Slider values in ACR 5.4 and the offset of Illuminant E, for example as shown here:



cheers,
« Last Edit: June 04, 2014, 12:05:51 am by xpatUSA »
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digitaldog

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #3 on: May 30, 2014, 12:05:43 pm »

Tint is the opposite color axis (magenta to green) from temp, what the exact offset is, is unknown and further, are we considering that the illuminant exactly follows the theoretical behavior of the black body curve (Plankian)?
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xpatUSA

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #4 on: May 30, 2014, 12:57:46 pm »

Tint is the opposite color axis (magenta to green) from temp, what the exact offset is, is unknown and further, are we considering that the illuminant exactly follows the theoretical behavior of the black body curve (Plankian)?

That would 'Planckian' would it not? No, I am not considering that the illuminant exactly follows the theoretical behavior of the black body curve.

So, I take it that you don't know the numerical relationship between a distance along a temperature line on the above chart and the numbers above the ACR tint slider.

Thanks anyway,
« Last Edit: May 30, 2014, 12:59:29 pm by xpatUSA »
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Schewe

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #5 on: May 30, 2014, 01:23:48 pm »

So, I take it that you don't know the numerical relationship between a distance along a temperature line on the above chart and the numbers above the ACR tint slider.

I doubt there is a direct relationship...the tint slider has arbitrary units and it would not translate to a specific mapped unit (as far as I know). Perhaps Eric might chime in, but I don't think there's a way to do what you want to do. Also, the Temp numbers are also not "pure" units, but more relative units. While ACR and LR have the same units, other software will not. So, D5000ºK in one app won't  necessarily match with another app. It's all pretty much relative...
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digitaldog

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #6 on: May 30, 2014, 01:56:14 pm »

So, I take it that you don't know the numerical relationship between a distance along a temperature line on the above chart and the numbers above the ACR tint slider.

Nope because YMMV (as will the numbers).
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sandymc

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #7 on: May 30, 2014, 02:22:12 pm »

The answer is (approximately, and with the caveats laid out above by others):

Temp = 5455K, tint = -12.95

This only applies within "Adobe world" - other raw converters may have a different view.

For those interested in the technicalities, tint in Adobe world is 3000*distance of the point in uv space from the black body line.

Sandy
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xpatUSA

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #8 on: May 30, 2014, 02:25:45 pm »

Thank you so much, Sandy,

Just what I was looking for!

cheers,
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bjanes

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #9 on: May 30, 2014, 07:22:30 pm »

The answer is (approximately, and with the caveats laid out above by others):

Temp = 5455K, tint = -12.95

This only applies within "Adobe world" - other raw converters may have a different view.

For those interested in the technicalities, tint in Adobe world is 3000*distance of the point in uv space from the black body line.

Sandy

That is interesting information, but are there any real world Illuminant E sources, and, if so, what would be the advantage of such an illuminant.

Bill
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xpatUSA

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #10 on: May 30, 2014, 09:11:44 pm »

That is interesting information, but are there any real world Illuminant E sources?

None that I know of, just as there are no real D50's, D60's, etc.

Quote
. .  and, if so, what would be the advantage of such an illuminant?

None, per se. I'm playing with an idea and the ability to set a WB in post to emulate illuminant E will help.

cheers,
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digitaldog

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #11 on: May 31, 2014, 11:55:08 am »

None that I know of, just as there are no real D50's, D60's, etc.
D50 is based on real, actual measurements of daylight albeit taken around the world at differing times for an average. Illuminant E? don't think so:

Quote
Illuminant E is an equal-energy radiator; it has a constant SPD inside the visible spectrum. It is useful as a theoretical reference; an illuminant that gives equal weight to all wavelengths, presenting an even color. It also has equal CIE XYZ tristimulus values, thus its chromaticity coordinates are (x,y)=(1/3,1/3). This is by design; the XYZ color matching functions are normalized such that their integrals over the visible spectrum are the same.[1]

Illuminant E is beneath the Planckian locus, and roughly isothermal with D55.
Illuminant E is not a black body, so it does not have a color temperature, but it can be approximated by a D series illuminant with a CCT of 5455 K. (Of the canonical illuminants, D55 is the closest.) Manufacturers sometimes compare light sources against Illuminant E to calculate the excitation purity.[18]
http://en.wikipedia.org/wiki/Standard_illuminant#Illuminant_E
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xpatUSA

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #12 on: May 31, 2014, 02:58:48 pm »

D50 is based on real, actual measurements of daylight albeit taken around the world at differing times for an average. Illuminant E? don't think so:
http://en.wikipedia.org/wiki/Standard_illuminant#Illuminant_E

It was Bill Janes that asked the question re: illuminant E. So perhaps you should respond to him, not me.

cheers,
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digitaldog

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #13 on: May 31, 2014, 03:22:24 pm »

So perhaps you should respond to him, not me.
There are real world Illuminant D sources.
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xpatUSA

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Re: White Balance and Photoshop's Tint Slider Calibration
« Reply #14 on: May 31, 2014, 03:42:49 pm »

There are real world Illuminant D sources.

I doubt this rather terse claim.

CIE's Illuminants are all theoretical sources of visible light with profiles (spectral power distributions) which are published. They provide a basis for comparing images or colors recorded under different lighting. (paraphrased from the WikiPedia page).

In the good old Real World there are sources that attempt to emulate D sources - which I suppose is what you're trying to say.
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