>>>>>>>>>>
By itself the RGB sensors can't determine this without a baseline for the
determination. But there are more pieces of information gathered by the meter
than just the colour values. The brightness and contrast of the scene are also
obtained.
<<<<<<<<<<
I think you're on the right track. What you wrote reminded me of a post
made last year, which I've found in the archive.
On February 14, 1997, Christoph Malin posted (I'm quoting parts of the
original post here):
>>>>>>>>>>
Have not been on the list for a while, have much work to do. In the
meantime I did another interview with a Nikon Rep in Japan for my Photo
Secretary article. OK, once again, those infos are excerpts....
Q: How does the F5 meter a plain white or plain black wall in the sunlight ?
A: With F5's 3D color matrix metering color data of the subject is added to
the parameter to make better exposure. However, pure white wall or pure
black wall is monochrome and is same as gray in terms of color data. Thus,
such a extreme scene can not be determined as color data. Also, if there is
no subject around to compare the contrast with the wall it is very
difficult for the camera to assume reflectance. The basic mechanism of this
metering is: The data of *color, brightness and contrast and focus area
signal are compared to the camera's built-in database of *more than 30,000
scenes* taken from actual shooting experience*.
<<<<<<<<<<
That might explain why some claim the F5 can photograph white snow as white
while others say it can't. If there's enough else in the scene (say, blue
sky) for the meter to get a sufficient contrast measurement, the RGB meter
may be able to tell the snow is indeed white, while it may be unable to
make such a determination lacking something to contrast with the snow.
Larry
