Digital BW, The Print

Jeff writes:

> Can you tell me why this is the case?

Two reasons:

1) All current digital cameras are color cameras.  The continuous spectrum
of light in the original scene is reduced to three numbers, for red, green,
and blue.  It is not possible to convert these three numbers to a grayscale
rendering of all the possible B&W images that could have been taken of the
original scene, because the recording in RGB deletes most of the necessary
information for this.  You cannot duplicate the results of a narrow-band
yellow filter on B&W images with any manipulation of the RGB color image
from a digicam, nor can you duplicate the results of a specific spectral
sensitivity in B&W film by any conversion of RGB to grayscale.

2) Since color digicams receive only one color per pixel, and then
interpolate, B&W conversions of these images are lower in resolution and
higher in noise than would be true original B&W image captures.

Both of these problems would be solved by a true B&W digital camera (one
without a matrix color filter in front of the sensor, and one that recorded
the image directly in grayscale).  However, nobody currently builds such a
camera, and image sensors are not interchangeable.

> If I wanted to make an 8x 10 B&W print using a hextone
> ink system From a 6 MP digital SLR raw camera
> file (that has me carefully processed and converted
> to grayscale) as opposed to shooting a B&W medium
> format neg and scanning it.... what would be lacking?

That depends on to what you compare it.

The results of certain types of filters in B&W photography cannot be
duplicated by any manipulation of a RGB color image; however, you can
duplicate them by using the same filter over the camera in the original
shot.  I've already mentioned the example of a narrow-band yellow filter,
which is a very simple illustration, but there exists an infinite number of
combinations that cannot be rendered by conversion of RGB.

A more difficult problem is rendering the spectral sensitivity of a specific
or theoretical B&W film, which simply isn't possible at all without shooting
with that kind of film (unless you have a very special, custom-made
correction filter over the lens when you shoot in RGB).

Note that this problem exists for conversion of any color image to
grayscale, whether the color image comes from a digital camera or film.
It's just that you can shoot real B&W with film, whereas no digital camera
allows you to shoot B&W directly.

Put more simply, you can never precisely duplicate a Tri-X look without
shooting Tri-X, nor can you duplicate the look of Tech Pan with a
narrow-band filter, nor can you duplicate just about anything else
perfectly, or even approximately.