Predictive color temperature model

[msf245]

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 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)

 

[markmullen]

I'll do some for you, the only issue might be the size of the file being too big to email.

I'll geotag it too.

 

[msf245]

Perfect! If the images are too large to send over email, can you crop it (to just include a portion the white balance card) or shoot at a lower resolution? Please send me a PM or email if you have any other questions. We really appreciate the help!

 

[HoppyUK]

Sorry to say I don't think this will work.

I use a lot of different cameras and lenses for work, in controlled conditions, and they all vary slightly. Lenses have different colour characteristics and cameras too, even when set to the same K value. So, if you then import them to say Lightroom and neutralise the test target, you will get some quite different numbers even though the colour of the light is actually the same. This would be easy to test for yourself - same target, same light, with different cameras and different lenses. I would guess this would be your most significant variable.

Secondly, I'm not sure that the colour of noon day sun varies that much internationally, except maybe towards the poles (warmer). For sure, when we all used film, it was the same 'daylight balanced' emulsion at 5500K sold around the world.