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12-03-2015, 03:21 AM   #1
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From failure to measure

I had a misshot and took picture of my red socks. The problem is that they are brown or black (really dark) in the picture. I blame the lightning as I can do that thing with only one lamp.

I have socks in my feet but in my hand I have light sensor system called camera. Can I use it to create some kind info of CRI or spectrogram of the lighting? I tried white paper, but quickly brutalizing some .tiffs with matlab didn't give anything useful.

12-03-2015, 03:40 AM   #2
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check the white balance setting in the camera and use the histogram to get a good exposure.
12-03-2015, 04:20 AM   #3
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As for the exposure bit, you could use a gray card, or you could do it by eye, or using the back of your hand (if caucasian it'll be 1 stop lighter, on average).
As I believe you already know, the meter of your camera meters for middle gray, so it will underexpose a mainly light scene (snow), and overexpose a mainly dark scene (the classic black cat).
12-03-2015, 05:16 AM   #4
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If color accuracy is the issue, know that with even the correct white balance, you're not going to get perfect color if the light source doesn't have a full spectrum. And as mentioned above, using a gray card is really helpful if you have software like Photoshop. If you can't use your flash, and your WB white balance settings match the light source, then your light levels or ISO is probably just too low. Are you shooting RAW or jpeg?

12-04-2015, 04:40 AM   #5
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Color accuracy isn't the real problem yet at least. In my tests I've set white balance to daylight. This gives wrong colors but it's always the same way wrong and matches best my house lighting. I use too expensive 965 fluorescent light in my house.

My studying of color started with poor CFL (CRI 82) and then I've tested some colorcharts and white paper under different light. I've placed them on grey target so that about 75% of picture is grey. Sun hasn't shined so I haven't been able to go out and take a good reference. And I know that I can't see object if there isn't color emitted from light source which the object reflects. I wont give in just yet. I have some ideas how I might be able to do this.

However I think I'm not able to get the light info and CRI value from light with camera that easily as it isn't designed for measurement device even it would be nice information to know how bad light really is.

And I'm shooting raw always as I want to do something with the data which my camera gives me

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