[Leica] Re: Color anomalies

[lrzeitlin at optonline.net (Lawrence Zeitlin)]

On Dec 14, 2006, at 12:03 PM, Frank wrote:

> As I understand the problem... it occurs when there is a piece of  
> black synthetic clothing present.  The IR reflection off the
> synthetic part of the cloth is enough to be recorded by the sensor  
> in an erroneous way ( to our eyes), giving a magenta cast to the
> black sweater.
>
> As far as I can tell, the effect is "available" anywhere.  It is  
> the source of light plus the type of material that makes it go
> astray.  It is not an "indoor" or "outdoor" effect.  You need  
> filters all the time to ensure there willnot nbe a problem.
>
> The other part of the question, in my mind,  has to do with the  
> color of the clothing... is it black only or is the effect most
> obvious with black, but always present, in less obvious amounts,   
> otherwise.....
>
> All of which is why I think the addition of a filter in front of  
> the lens is a solution that is not-consumer friendly.  The filter
> should be included in the coating on the sensor cover plate.
>
> Question... I remember wedding photographers having trouble with  
> certain situations where the color of the white dress did not work
> on certain films.... something to do with optical brighteners in  
> the cloth of the dress.....   Can someone comment on this old
> phenomenon and its solution?

The way colors appear to the eye and the way they are recorded on  
film and by electronic sensors is different. The eye and the  
associated brain have a relativistic way of perceiving color. It is  
not only the physical wavelength of light that determines the color  
we perceive but its relationship to surrounding colors, the colors  
that have been seen earlier, and the overall color cast of the light  
illuminating the scene. That "white" paper that you are looking at  
under a reading lamp may appear distinctly yellow to someone standing  
outside in the sunlight and looking at it through the window. In  
photographic terms, the human eye has automatic white balance. No  
color filters are needed to correct for the difference between  
incandescent light and sunlight. We simply "know" what color we  
expect to see and we see it. The eye responds to the predominant hue  
and ignores any discrepancy. The pretty reds and yellows of fall  
leaves are there all year around but in midsummer, the eye sees the  
predominant green. It is not until the green fades that the other  
colors are perceived. It has been said that 80% of what we see occurs  
in the brain, not in the eye.

Film or sensors have no ability to "correct" the color of the scene.  
If a magenta hue is reflected from a black polyester sweater, the  
sensor sees it. It may be said that the M8 records the colors  
truthfully while the eye/brain combination makes the colors conform  
to expectations.

Larry Z