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Author Topic: Predictive color temperature model  (Read 4609 times)
msf245
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« on: July 30, 2013, 12:00:41 PM »
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I’m a student at Cornell University working on a design project aimed at creating a formulaic model to predict the color temperature of sunlight at any time and geographic location in the world.  Our algorithms are well on their way and we need empirical data to verify our work.  Thus, we are turning to the online photography communities to help us out!

We are asking people from all around the world to capture the color temperature of direct sunlight on a, preferably, sunny day by photographing (in RAW) a white balance card pointed toward the sun.  From that image we’ll determine the color temperature and add it to our growing dataset.  While we want pictures taken at any time of day and sun position, the white balance card must be placed in direct sunlight.

Please send all photos (in any RAW format) to msf245@cornell.edu and include the following information in the email:
-Location (lat/long, if possible)
-Time
-Weather description (brief: cloudy, clear, overcast, a picture would work as well)


Note: a white piece of paper is used in the photo - I didn't have my white balance card with me that day and used the paper as a "prop." A real white balance card should be used.  Thanks!


Also, if anyone is curious/doubtful, I went to a local camera store to look into the variations between different body/lens/white balance card combinations and have found the differences to be minimal (100-200K tops).  For what I want to accomplish, this uncertainty is acceptable as I'm more curious about tracking large-scale trends.  Within the lighting businesses, it is standard to call anything with +-125K the same.  Here are the results from my "study."



Thank you in advance!
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Guillermo Luijk
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« Reply #1 on: August 04, 2013, 04:29:36 PM »
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How does your algorithm deal with climate diferences? depending on the season, humidity, presence of clouds,... light can vary a lot for the same location and time.
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Hening Bettermann
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« Reply #2 on: August 05, 2013, 04:03:22 PM »
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This sounds like a great idea. If it can be done, may be a different question. May be difficult. My first question: How do you expose the white card in direct sunlight on a cloudy day? If you wait for the sun to peep through, the WB will not be "cloudy". Anyway, a very interesting project. Maybe I should get me a white card…
Best wishes - Hening.
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Hening Bettermann
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« Reply #3 on: August 07, 2013, 03:13:08 PM »
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Another concern: The white card will partly be lit by light reflected from the surroundings, like the buildings on your photo. It will be so to speak impossible to avoid this. The sun itself photographed through a diffuser may help. But this may limit the number of participants.
Best wishes! - Hening.
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