How to Preserve Colors

Question

I have a set of photos taken of different color objects illuminated by different types of lights at night along with a photo of each object in daylight.  Color temp of the lights ranged from 2000K to 6000k. I want to show the difference in color rendering between the different light sources.  I don't want to "improve" the photos -- just show the color distortion as it was -- that's the point.  Photos were taken on a Nikon D50 SLR in raw with auto white balance.
My question is:  I've used "as shot" white balance when importing into Photoshop.  Is that correct?  I'm concerned that the white balance computed by the camera will be used and will distort the original colors.

Answer 1

I'm looking to render whites (and several other colors) at the same distorted color captured by the camera due to differences in the spectral composition of the light used for the scene
There is no such thing as "preserving the colors" but "reproducing the colors", because the camera's way of recording the image is different from what you get at the end (already the thread title How to Preserve Colors showed this misconception).
The pixels of a camera with Bayer type sensor are often described as "red", "green" and "blue". This is comfortable, but incorrect; the pixels should be called Rgb, Grb, Brg, i.e. "mainly red, somewhat green, somewhat blue", the other one "mainly green, somewhat red, somewhat blue" and the third one is "mainly blue, somewhat red, somewhat green".
Let's see an example created with your camera (the sample is from Imaging Resources). We concentrate on the red, green and blue patches of the color checker card. The captures show a crop from the raw, i.e. undemosaiced, non-WBd image. The first capture shows the image in "composite color" mode: the "red" pixel value was used for the R component of RGB, the "blue" pixel value for the B component, and the average of the two "green" pixels became the G component.
The patches appear blue, green and red, more or less. But how are they really? The following captures show only the red, the green and the blue components. If a patch were red, then the green and blue component would be null (black in the display), likewise with the green and blue. Is that so?
It is obvious, that the "natural" color component is the strongest, but the others are far from being black.
The next issue is, that this appearance does not depend only on the color of the object and on the illumination, but on the sensor (on the filters over the sensels) as well. Look at the same patch under the same illumination, created by the D90. It is close, but not identical to the D60:
Again, all the above was without white balancing.
If you want to show, how the D60 (but only the D60!) records a scenery under a givel illumination, you have to use a neutral white balance. First, create such a template shot. The easiest way (though not all cameras like this) is to make a shot of something, which totally clips, like the cloudy sky or a white sheet, at least three stops overexposed (do NOT shoot the sun). Then use this image for setting the custom WB in the camera and select "custom WB" for the demo shot. Now the colors are not adjusted to the illumination.
This is still far from what the camera captured, but somewhat closer. If you want to see really the captured data, use Rawnalyze (free): http://www.cryptobola.com/PhotoBola/Rawnalyze.htm
Gabor