Yeah, you figured out the columns

No, the test isn't flawed. First, what is photographed has no effect on the temperature reported only on the color swatches. The illuminant I used was a white LCD display not incandescent. If you believe the numbers my LCD panel as adjusted is about 5550K which makes sense given the specs on the display.

Bill

Visit me, info and galleries at: Nikon Photos and Information

Only heat radiating light sources (the sun, tungsten lights) have a real color tempereture = a continous spectrum = Kelvin degrees.

Measurements of other light sources (mecury vapour lamps, flourescents lamps and lcd screen with fluorescent back lighting) will only give approx. and not true Kelvin values. The spectrums from these light sources are not continous. They are characterised by having missing wavelenghts and spikes at certain points in their spectrum.

best regards

Tom

I'm aware of spectrum differences (and the principle of metamerism).

White Balance values defined along the Planckian locus are entirely theoretical and are based on a specific spectrum.
These WB values, indicated in degrees Kelvin, have specific coordinates in any color system such as CIExy. Correlated color temperature and tint are widely used to describe the WB characteristic of any illuminant.

All of the illuminants you list are "heat radiating" (as is everything in the universe). They all have different spectrums. They all have a WB value in correlated color temperature and tint.

The test is totally valid and I'm sure repeatable with other light sources. With another light source only the last column would change.

Bill

Visit me, info and galleries at: Nikon Photos and Information

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Matthew J. Parry-Hill and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

best regards

Tom

Yes, they are describing metamerism and I agree.

Never-the-less corrected color temperature (with or without tint), although imperfect, is a useful measure.

That said, I agree that unless I use the same (unspecified) illuminant as Nikon that "my mileage may vary".

Bill

Visit me, info and galleries at: Nikon Photos and Information

My intention was to just to underscore, that assignning genuine Kelvin numbers to non black body radiators might (and sometimes do) mislead beginners into thinking that dialling the corresponding Kelvin value in the camera would lead to correct color rendering. The obvious color casts often seen from fluorescent lighted objects would then seem to indicate a faulty camera. BTW, I visited your website and read your observations on the D70 histogram with great interest. I am looking forward to test the D2X and have been promised that the channel specific histograms should be very precise. (also curious to see if the D2X offer enough improvement over to D70 to justify not waiting for an even better sensor with greater DR. I don´t need more pixels, but larger buckets for the photons)

best regards

Tom

Yes, if it wasn't obvious; I agree that a single whitepoint value is insufficient to describe a lighting situation.

And thanks for taking the time to examine my site and for digesting some of my other research projects.

When you get your hands on a D2X please send me a private message or e-mail. Perhaps we can collaborate on some research.

Best Regards,

Bill

Visit me, info and galleries at: Nikon Photos and Information

I dont know how a real kelvin meter works so... but since you got a consisntent result of 3000, makes me suspicious....

I dont know anything about this im just guessing cause I like to see you hard at work convincing me Bill

heheh

Chris

Check out some of my D70 shots:

http://nonex.doesntexist.org/

Yeah, sure, push my buttons, make me tell you eveything.

The camera does not compute a color temperature in degrees Kelvin.

It computes two ratios: red to green and blue to green. This is all that is stored in the Raw or Jpeg file. Important: it only does this computation if you choose Auto; otherwise it just uses the ratios that correspond to the WB you have chosen. (That's why for Incandescent I always get 3000 degrees with a tint of 1.)

These ratios specify a point in a colorspace; typically people use the CIExy colorspace. "True" whitepoints computed using a "blackbody" formula and a particular spectral response also have points in the colorspace. These are the color temperature points. Each of these "true" whitepoints also has points nearby with that are called "correlated" color temperatures and a "tint" value that tells you how far from the "true" color temperature you are.

Now, you can take the CIExy coordinates that results from the ratios computed in the camera and work backwards to the correlated color temperature and tint. This is what Adobe Camera Raw does when it displays the "As Shot" temperature and tint.

Did you follow that at all or are you just grinning?

Bill

Visit me, info and galleries at: Nikon Photos and Information

LAST EDITED ON 04-Mar-05 AT 03:13 AM (GMT 1)
 

Get some sleep Bill
That's what I'm gonna do...

*confused*

Chris

Check out some of my D70 shots:

http://nonex.doesntexist.org/

Visit me, info and galleries at: Nikon Photos and Information