10/23/2001
An old black and white photo could be a contact print from a 4x5 negative which can give an extremely high definition print since there is no enlargement. It would be approximately equivelent to a "16k" image which means that it would have 16 thousand lines of resolution in the most resolved direction. This would be about 3,200 ppi like you state. A 2 to 3 megapixel camera has about "2k" lines. My Fuji 4700 for example makes a file 2400 x 1800 pixels or 2.4k. Clearly this is much less resolution in the same sized print. It works out to 480 pixels in the 5 inch direction.
Here comes the meat. At a typical viewing distance a normal human cannot resolve more than about 300 ppi, so in both cases resolution is wasted. The Fuji camera could make a decent 8x10 print. Now if you pull out a magnifying glass certainly the contact print will win and look better. Continuous tone digital prints are typically made at 300 ppi since that is all your eye needs. This is different on an inkjet printer because an inkjet printer does not print each pixel at one of millions of colors, but rather at one of 4 to 6 colors. The input file on an inkjet would still only require 300 ppi, but the output resolution of the inkjet needs to be as high as possible in order to blend the individual ink colors into the millions of colors we need to see.
Back to the original old black and white photo reference. Can digital match that quality? Well, it cartainly depends on what the original quality is. There are of course many poor quality old potos. Old black and white cameras ranges from cheap "point and shoots" to high quality press and studio cameras. Our 16k example image came from a good camera with a good lens and was processed properly so it has great sharpness and tonal range. It will be a while before digital can match that. Digital already surpasses the lower quality stuff though. In fact IMHO $300 digital cameras already have passed $300 APS cameras in quality and most definately have surpased 110 film. This means that 35 MM is next.
We haven't gotten into the color issue much, but Digital cameras (this applies to scans as well) can have color casts and they can be non-linear which means that you can get an effect called "color crossover". This is bad since it is possible to have highlights of one color, say yellow, and shadow areas of the opposite color, blue. If you try to correct out the yellow of the highlights, the shadows just get more blue. Guess what? Traditional color film and paper is subject to the same problem. It's just that there is no way to correct it other than years of research to make sure the film is matched to the paper, which is what the industry has done. The Digital industry hasn't gotten there yet, although it is much better today than even a year ago if you can believe it. One nice thing about digital and this crossover thing is that you can generally correct the tone curve after the image has been made. At this point it takes expertise to do it, but not too much more than it takes to color correct a traditional color print. Some things are extremely easy to correct. It is trivial for example to bring out detail in a slightly too dark shadow area in a digital image. Just grab the middle levels slider in Photoshop and "presto". Magic that is impossible in traditional photography. We won't get into all of the things that are possible with a digital image that just aren't with traditional. But here's another one. How about archiving a large quantity of images on to a single duplicateable piece of media that is searchable?
Which camera should you use? Well, if you are for some reason using a 110 camera, throw it away and get the cheapest digital camera you can get that has a color display on it. You'll take better pictures. If you are using APS, seriously consider switching to a good quality digital camera. If you are computer literate as well, then do it today. 35mm disposeable, see 110 (They call 'em disposeable for a reason). If you are using a 35 mm point and shoot, then you will have to do some research. Borrow a few digital cameras. Try out some of the digital labs. (Plug for my employer here http://www.bayphoto.com ). Make your own decision. If you are an amatuer or pro using a 35 mm SLR or larger then you likely already know what your needs are and perhaps learned a little from my little writing here.
Personally, I use a range of cameras. I have about 20. My favorites are a Pentax 35mm SLR with autofocus and built in flash, which can be set to full manual, a Fuji 645 format autofocus camera which amazingly is very much like a point and shoot since it has autowind and a built in flash, a Pentax 6x7 (let me know when digital gets _there_!) and finally my Fuji 4700. Which do I use most? I bet you can guess. It surprised even me to realize I have taken thousands of photos in just over a year. I tend to cover an event much more thoroughly since I don't have to worry about the cost of processing and since the camera is so small I can always keep it with me. Kind of shooting myself in the foot since my livelyhood depends on photo processing.
Hope that helps someone,
Wolff
"Nobody can forget the sound." - Michele Mouton