jbandy wrote:
...I just did a test with an all white background and using a random subject (stuffed animal) and still get the warm result.
I analyzed your samples in Elements, and here's what I found:
In the AWB sample, the background read pretty neutral, and the gray card read slightly cool (R-75, G-78, B-83 at one point).
In the Grey Card sample, the background read slightly warm, and the gray card read dead-on neutral (R-78, G-78, B-78).
The next test would be to fill the frame with the gray card and repeat the AWB and Grey Card tests; that will rule out a color bias in your background. ("White" paper is rarely pure white.)
I'll happily use he Expodisk when there is mixed light - I find it does a very good job of averaging out the colours.
But for studio work I find I can now only trust a genuine Kodak card. Either the white or grey sides - they are exceptionally accurate and the material is nice and matt to give better results.
It doesn't take much for a card to give poor results. Paper, whites of eyes, cheap grey cards... all give poor results.
jbandy wrote:
...Hopefully this is what you needed.
Perfect. Thank you.
That AWB image reads very neutral, varying only slightly from location to location. I'm reading 76-78-77, 77-76-75, etc.
The Grey Card sample is even more consistent, reading 73-73-73, 75-75-75, and so on.
I had been wondering if the AWB on your camera was applying a color shift, or if your gray card wasn't true gray, but it looks like that's not the case. I think your background paper was throwing off the balance in the first examples, and actually is a little on the warm side.
jbandy wrote:
...It still seems warm sampling off of the grey card doesn't it?
Yes, assuming the whites of the bunny's eyes are actually white, it is reading quite warm. But the gray card is reading on the cool side. It's perplexing.
I don't know how you're lighting it, nor what your work flow is, of course. I'm afraid I can't help you with that; it looks like some more reading and practice are in order.
That is because the light on the grey card is bouncing off that blue surface. Put the grey card up cam left side of the bunny head and it will be more accurate, but then the areas of the bunny closer to the blue will be bluer. Product photographers would shoot this on a neutral background, then knock it out, or cut it out, and then put it on blue. And of course color correction is the main reason for that technique.
To prove what I said above to yourself, correct the white balance off that grey card from two areas, one near the top, and one near the bottom. You will find that when you use a point from the bottom of the card the image goes much warmer, because more blue is being reflected there. So where do you sample from to get the correct white balance... Well, you don't, that's the whole point. That's why you need to shoot neutrally and do post work. But in general put the grey card in the dominant light, which I suppose would be next to the Benny's head in the direct light, still won't be perfect though.
This example exemplifies the complexities of getting wb "correct" though. To do it right every area of the bunny would have to be adjusted differently: the areas closer to the blue would need more warmth, and the head may need only a little warmth added.
First, unless your lighting is tightly gridded, there is no way you won't get a color cast on your subject sitting on the blue BG. If you want accurate color get a Color Checker Passport. Not all grey cards are equal either. With a passport you can pick the temp you like best and build a profile you can use later for that lighting setup.
It can also be due to your light modifier. Are you using a softbox and is it a good one? The cheapies can cause a color cast as well.
