Digital BW, The Print

Mark writes:

> Umm, we are mixing pixels with sensor elements here.  Sure, the
> typical CCD does not provide a true rgb pixel for every sensor
> element, it has to interpolate one from adjoining elements which
> means your effective pixel area is larger than any individual sensor
> element, but that doesn't mean that information is being "thrown
> away" ...

Yes, it does.  Since each photosite on the sensor receives only one primary
color, the information for the other two colors is being thrown away.
Overall, 2/3 of the total RGB image information is lost; software simulates
the lost information by interpolation, but simulation is not recovery.

> Sure, a true and instantaneous scan of each rgb channel
> would be preferable, but in real life there are so many
> variables in film scanning that the benefits are probably lost...

I can see the benefits pretty easily.  Colors bleed on digicam photos
because of the interpolation.  They do not on film scans.

> When you convert to gray scale you don't necessarily "lose"
> quality over your rgb information, you are just getting there
> in a terribly inefficient manner...

No, there is an actual loss, and it is quite significant, particularly with
digicam photos, since they've already sacrificed 2/3 of the RGB information.
Even in the case of color film, however, the RGB capture throws away most of
the image information in the original scene, and so almost all the
flexibility of true B&W capture is lost.

The only way to have the full flexbility and depth of information of black
and white is to capture in black and white to begin with.

> ... comparing scanners and digicams and making a blanket statement that
> you get 3 times the information from a scanner is really misleading
> at best.

No, it is 100% correct.  Film captures all three colors.  Individual dye
clouds are much smaller than scan pixels, so each pixel contains information
for all three primaries in a film scan.  In digicam photos, 2/3 of this
information is absent.

> Then why the heck would anyone shoot Technical Pan
> film then????

Technical Pan has even higher resolution and even less grain.  I said
"similar to," not "equal to."

Portra 400BW is a good compromise when Tech Pan is not practical or
possible.

> I can't even conceive how anyone can make this statement?

Neither can I.  If anyone ever actually makes that statement, you may want
to ask him about it.

The rest of your questions on this point and the many question marks that
follow them are moot, given the above.

> I don't think there is a real argument here anyway... just
> semantics...

There is a real loss of information in digital capture versus film capture,
even for equal numbers of pixels.  In addition, all conversions from RGB to
B&W involve an enormous loss of information compared to straight B&W
capture, and this is true whether the capture is digital or film (although
it is slightly worse with digital capture).