Digital BW, The Print

Black and white film is an power sensor. It simply measurses the power 
(it counts photons) at a location on the film. A CCD is a power sensor. 
It only counts the photons at a location. The only reason it can 
measures red or green is there is a filter in front of it that filters 
one all but one single frequency photons. Light is not only made up of 
three frequencies - it is a continuum with the visible spectrum being 
from a little above IR to a little below UV.

So the question is how well can one predict the actual energy on a pixel 
per pixel basis using only pixels from there discrete frequencies.

It is a very easy experiment to run and it has been run many times. Take 
a CDD without any color filter and measure an image. Measure it with 
three sensors one with red, green and blue filters. Now take the entire 
scene and minimize the error of the between a weighted combination of 
the R, G and B sensors and the output of the CCD without any color 
filter. There is a set of weights that minimize the error, but the error 
will not be zero. That is the information lost.

Now does that make a difference to the observer - to some it will to 
some it won't.

Truman

Clive Moss wrote:

> Anthony G. Atkielski said the following on 4/11/2004 5:26 PM:
>
> > In summary: if you want to shoot black and white, you must _capture_ the
> > original image in black and white.  Converting color always gives an
> > inferior result.
>
> You can't capture the original image in B&W. It is in color. Mapping it
> to B&W involves a series of implicit decisions about what brightnesss to
> assign assign to a specific colored point.
> For film, the decisions are made by the folk who designed its spectral
> response, modified by the photographer who may use a filter.
> For a digital capture, the decision about the relative balance could be
> delegated to the camera manufacturer by switching to a B&W mode, or
> control could be maintained by the photographer by by playing with the
> RGB balance in channel mixer. This may or may not be inferior to the
> manufacturer's setting.
>

-- 

We imitate our masters only because we are not yet masters ourselves, 
and only

because in doing so we learn the truth about what cannot be imitated.

 



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