A few weeks ago, there was a discussion of the relative merits of film versus
digital, with the metric of goodness being how large an enlargement each format
would support, and it appears that visual sharpness was the issue.
There is a bit more to it than that. Color (and grayscale) fidelity very much
depends on the dynamic range and intensity resolution of the recording media.
This is always true, regardless of the media, silicon CCD or silver-based film.
The science is that the human eye uses subtle gradations in intensity and color
to infer the 3D shape of a subject from a 2D image of that subject. This is
true on the retina viewing a 3D world, and certainly true when viewing a
photograph. If the fidelity is insufficient, the photo will look flat. The
higher the fidelity, the more the photograph will look more like a window
framing the subject and less like a snapshot.
With a given kind of film, the grain is of constant physical size on the film
surface. The larger the negative, the smaller the grain (noise) is compared to
an optical resolution element in the image, and the higher the effective
dynamic range.
In black and white, this makes the tonal gradations smoother and more accurate.
Ansel Adams was the master of this, and wrote extensively on the issue.
With color, each of the three color layers is in effect a black and white film,
and so the larger the negative the smoother and more accurate are the
gradations in each color, leading to more accurate color rendition in addition
to smooth and accurate total intensity.
This is why photos for magazine ads are done on 4x5 minimum, with lots of 8x10
being used. The minimum is medium-format, used for ads in newspapers (with
less resoultion than slick magazines). News photos are usually 35mm, however.
The CCDs used in digital cameras have a parallel problem. The smaller the
pixels (microns by microns), the lower the dynamic range of the image, the less
sensitive the camera, and the noiser the image. Scientific CCDs tend to have
big pixels (to capture and hold lots of photoelectrons), and also to be cooled
(to reduce dark noise).
At my company XMAS party, somebody was using a 2.1-megapixel point&shoot with a
built-in pipsqueak flash. The photos were terrible -- looked flat and
cartoonish, especially faces. Part of this was due to the photo exceeding the
gamut (color range) of the inkjet color printer, but the photos weren't that
great on the screen either. They would have been far better off with a film
camera, even a $10 disposable camera.
Joe Gwinn
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