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Author Topic: Three different color calculators can't be wrong, can they?  (Read 4828 times)
BartvanderWolf
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« Reply #20 on: September 03, 2013, 06:05:18 AM »
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The current practice is to use a colorimetric definition based on euclidean distance from the Planckian locus on the uv chromaticity diagram.

Mark is correct. See here as well.

Quote from: spie.org
There are limitless different spectra, all with the same CCT, that may have little or no resemblance to the blackbody curve for that temperature or to each other.

There is no approved method for computing CCT nor is there a simple and accurate closed-form expression. One simple and accurate method is to use a program such as Excel with solver to find the blackbody temperature that minimizes the distance between its (u, v) coordinates and those of the light in question.


Cheers,
Bart
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digitaldog
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« Reply #21 on: September 03, 2013, 09:54:42 AM »
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Excellent info from both Bart and Mark. I plan to archive both. Unfortunately it will fall on Franz's deaf ears. He really isn't interested in getting the facts. The post he made on PhotoNet the same day as the post here was locked down due to his stubbornness and inability to link this to anything related to photography. I tried to explain to him that by the nature of a color being correlated, we're talking about a possible range of possible colors.

His reply is classic Franz:

Quote
Calculating CCT from the x and y coordinates is rather complicated and different calculators use different algorithms, resulting in slightly different answers. However, these answers should not be more than a couple of Ks apart, and the answers from the three calculators that I used are within that range. However, the SoLux CCT number is way off, by about 44K, so that begs the question that SoLux sofar hasn't answered.

Answer: The Solux values are wrong! He's certain despite asking, that the values should be within a few K but since that dismisses the Solux values, he can't accept it. Apparently even Solux is ignoring him as should we. Troll alert!
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
Czornyj
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« Reply #22 on: September 03, 2013, 11:34:17 AM »
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It was obvious from the start - who on earth would care about few K of relative and almost completely meaningless CCT values when exact x,y values are given?
« Last Edit: September 03, 2013, 11:36:25 AM by Czornyj » Logged

papa v2.0
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« Reply #23 on: September 03, 2013, 04:49:15 PM »
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Best place for standard definition and method of calculation is the CIE

http://www.cie.co.at

refer to the International Lighting Vocabulary

That should help.
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Frans Waterlander
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« Reply #24 on: September 05, 2013, 11:32:18 AM »
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Andrew wrote: "Apparently even Solux is ignoring him..."
I've been doing what I advice others to do as well if they have an issue with a company's product: work with them. SoLux agrees with me that there is an issue with their x, y and CCT numbers and will rectify the situation. I'll give an update as soon as I get more definitive information.
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digitaldog
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« Reply #25 on: September 05, 2013, 11:53:33 AM »
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I'll give an update as soon as I get more definitive information.

We'll all hold our breath's in anticipation.... Much like your promise to discuss the CIE article that greatly dismisses your ideas about display calibration which you haven't reported on.

Oh and LuLa audience, Frans has accomplished getting two forum posts on PhotoNet locked down, an indication that he's on a quest of Tilting at windmills!

There's no situation to rectify, nobody cares!
« Last Edit: September 05, 2013, 11:56:26 AM by digitaldog » Logged

Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
digitaldog
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« Reply #26 on: September 05, 2013, 12:58:39 PM »
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There's no situation to rectify, nobody cares!

So Frans, you realize you can set a poll here on LuLa, a site that gets 1.1 million unique readers each month. You should investigate if anyone gives a crap. I'll even write the poll for you:

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Dear LuLa members. My name is Frans. I've found that the SoLux data about their bulbs is off by 6K for one bulb, 44K for another bulb and 213K for yet another one. Do you have an interest in why? Fill out this poll:

1. I care a lot, please let me know why!
I would rather know why this is, than if there is other intelligent life in the universe.

2. I'm not interested but I'll look over your findings.
Knock yourself out, I'll at least read what you found.

3. I don't see how this will affect the Solux units I'm now using.
In no way would the Solux marketing values have any bearing on what I'll buy from them, nor how I currently use their products.

4. I don't care one bit, this has nothing to do with photography.
You obviously mistake me for someone who gives a s**t!
« Last Edit: September 07, 2013, 03:50:37 PM by digitaldog » Logged

Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
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