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msf245
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Join Date: Jul 2013
Location: Ithaca, NY
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18-07-13, 09:11 PM
#1

Predictive color temperature model

Im 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 well 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 musts 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)



     
Bazza
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19-07-13, 08:24 AM
#2

Re: Predictive color temperature model

welcome to the group. Can't send you anything as my upload speed is only
0.51Mbps and sending a Nikon D800 photo in any Raw (45mb) or Tiff (109 mb) format would take until next year to do it . Sorry would love to have helped.

Have you taken into consideration different makes of camera produce a slightly different tone of picture or camera settings WILL make a difference to the card picture anyway. I can shoot the same shot with a Canon and a Nikon with same settings and produce a different tone. It again depends on the time of year as to the sun effect on the earth

May be , if I may suggest , you study a little bit about photography before undertaking your project because the way you want to do it will produce useless results.

If you take my advise there are too many variables

1= make of camera, different manufacturers use different sensors which affects the image
2= Camera settings ,major consideration
3= with or without filters
4= time of year even time of day as to sun brightness
5= memory cards can very slightly from make to make as regards to output
6= How to prove the target card is at the same angle every time by different people
7= are white cards exactly the same across the world ? don't think so texture/reflection varies
8= angle of card held, different angles reflect differently

To name but a few without even considering lens quality/make variations, which is a whole new subject.
Don't even think every lens produces the same results, far from it

If you actually studied light you would soon realise atmosphere has a strong relationship to how light reaches the earth in different parts of the world.

Take a look at a few photos taken at high altitude against those at sea level. The light clarity is vastly different, I noticed this in my USA visits especially in Yosemite National park

If I were you with all due respect I would suggest trying something else as any results would be very poor at best.



Bazza


     
msf245
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19-07-13, 09:08 PM
#3

Re: Predictive color temperature model

@Bazza, thank you for bringing up those points.

I have done decent amount of research on various sky models and have pieced together a version of my own. Right now, it take into account the position of the sun (according to the time of the day and day of the year), but I'm lacking data for other location to begin exploring the effect of elevation or air pollution, etc. on the color temperature - that is what I'm exploring here.

I fully acknowledge that while there will be some variations between cameras, lenses, white balance cards, etc, this is not a completely scientific pursuit and I expect variations. I have realistic expectations and am more curious to fit curves to subsets of the data I collect (holding certain variables constant) in order to tease out general trends. I am also hoping that with a large enough dataset, the slight variations between equipment, etc, would average out.

You are correct, though, that I should have been more specific in describing how I want the white balance card to be held. I am trying to capture mostly direct sunlight, so I have been trying to holding the card perpendicular (normal) to the rays of the sun. As for filters, I should have specified for the image to be taken without a filter or only have a UV filter on as it should not alter light at all in the visible spectrum at all.

With all that said, if you could still take some photographs and determine the color temperature on your end (in either in the camera or in your choice of software) and send the data that way, I would be greatly appreciate it!


     
Bazza
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19-07-13, 09:35 PM
#4

Re: Predictive color temperature model

See my first paragraph regarding sending photos I was wondering what you will do with the
Data collected. Have to be honest and say I can't see any practical use for it


     
msf245
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19-07-13, 09:48 PM
#5

Re: Predictive color temperature model

I read that you could not send the photos due to internet speeds. I was merely suggesting that you can send just the color temperature/white balance number and I can add that into the data set. I was only asking for the original image to do the work myself and verify that the image was taken in the proper manner (for which a jpeg would work).

Essentially, I'm crowd sourcing data points from all over the world to extract global trends of color temperature based on altitude, visibility, solar position, etc.


     
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