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Old May 21, 2012, 1:58 PM   #1
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Default Color change in a photo question

Okay guys and gals, I'm Stumped!

I took a bunch of family photos for my daughter over the weekend and I ran into something I have never had happen before. My youngest Grand Daughter (sitting on the right) had on a Lavender colored shawl type thing. In virtually ever photo I took of her the shawl was BLUE!



I was trusting the Auto white balance for that exposure, but controlling the ISO and the Aperture. Here is the EXIF:

Date Time Original: 2012:05:18 22:58:19
Exposure Time: 1/100
F Number: f / 4
Exposure Program: Shutter priority
ISO Speed Ratings: 250
Metering Mode: Spot
Flash: Flash did not fire, compulsory flash mode
Focal Length: 40mm
White Balance: Auto white balance
Make: Canon
Model: Canon EOS 7D
LensInfo: 4
LensModel: EF17-40mm f/4L USM

What the heck caused the color change?

Dick
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Old May 21, 2012, 4:10 PM   #2
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I would call it blue, from what I see.(somewhat towards purple in places) My guess is that the color shift is related to the program you are using to view the photo. Looking at the Exif info, the color space is shown as 'uncalibrated', which means Adobe RGB. If you are looking at it with something that isn't color space aware, there will definitely be a difference.
Part of it may be due to the auto WB, but I think most likely it is the Argb that is doing it. (looks like arrgh, doesn't it?)

brian
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Old May 21, 2012, 5:13 PM   #3
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Thanks Brian. The purple in places is the color the shawl should be. I use Adobe Lightroom 3.5 to edit. One tip I was told to try is to use the Purple slider to adjust the exposure, plus to use the Shade setting on the WB. It helped some, but I have more work to do to adjust the photo.

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Old May 21, 2012, 5:59 PM   #4
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When I open it to PI,and check the color cast by using eyedropper on the white shirts, it shows as being too much blue/cyan. Normalizing it gives it quite a lot warmer look.

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Old May 22, 2012, 12:08 AM   #5
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Thanks Brian! I'll work on that method!

Dick
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Old May 22, 2012, 4:07 AM   #6
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Interesting- I used to have a Fuji camera which did the same thing- in any conditions- anything lavender/purple etc came out blue...!!
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Old May 23, 2012, 12:08 PM   #7
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Too late now, but don't rely on a cameras auto-white balance.

When accurate colour is needed I use a Spyder cube or a GratagMacbeth target. to set the colour temperature for a given series of RAW images under the same lighting conditions.

You could also try setting a custom white balance using one of the many white-balance tools out there, like the Expodisc.
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Old May 23, 2012, 3:06 PM   #8
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Thank you Peter! I'll check into those right away!

Dick
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Old May 23, 2012, 6:06 PM   #9
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Quote:
Originally Posted by SIMON40 View Post
Interesting- I used to have a Fuji camera which did the same thing- in any conditions- anything lavender/purple etc came out blue...!!
I've lost count of the number of discussions I've seen on various digital camera forums over the years about that problem, usually when photographers are trying to capture violet colored flowers.

You'll see the same thing with same shades of purple

It's normally not a White Balance issue. You'll see tons of theories and technical discussions about it, ranging from papers about why violet is hard to reproduce and what the human eye sees is not really what the camera is recording.

For example, see this wikipedia article about violet, and note that spectral violet is outside of the Color Gamut that can be reproduced within the RGB color space (although you can get approximations via mixing red and blue, you can't actually reproduce spectral violet by mixing red, green and blue).

http://en.wikipedia.org/wiki/Violet_%28color%29

Keep in mind that the color filter arrays used by bayer pattern sensors in digital cameras are only sensitive to those 3 colors, too. A given pixel is only recording red, green or blue values, then they're combined during the demosaic process so that all 3 colors are represented at each pixel via interpolation algorithms looking at surrounding pixels (and you can't reproduce spectral violet by mixing red, green and blue).

Here's an old thread about the issue I found with a quick google search (and there are *many* similar threads about the problem):

http://forums.dpreview.com/forums/re...ssage=12622675

Again, I've lost count of the number of discussions and theories about this issue, ranging from inability to reproduce violet because of the narrow sensitivity of the color filter arrays (where each pixel is only sensitive to red, green or blue, with only RGB values being stored in current image formats), to cutoff frequencies of the UV filters causing issues with the violet end of the spectrum (since violet is closer to the UV end of the spectrum).

But, the problem is normally the same -- anything violet tends to show up more blue, depending on the lighting you're shooting in.

You'll see similar discussions about purple. Here's one article about it:

http://deron.meranda.us/ruminations/purple/
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Old May 23, 2012, 8:39 PM   #10
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I took another look, and did a small bit of editing in PI, to come up with something a bit different. After adjusting the color cast, the sweater was still very blue, so I tried adjusting the saturation down by 30%, and came up with the following result. I surmise that because the predominant color is blue, that increasing the saturation results in the blue color overwhelming the more subtle shades.
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