Does anyone can give me some hints (numbers if possible) to be able to compare digital photography with traditionnal photography.

What is the theorical resolution of a classic 35mm shot if we consider we use the best lense, the best film and the best scanner avalaible on the market.

How this theorical maximum resolution is diminished with the lense and/or the film quality.

-- Jean-Sibastien Rousseau-Piot (jsrp@caramail.com), March 20, 2000

Answers

I wouldn't worry about the theoretical resolution figures if I were you, Jean-Sebastien. Practical differences are sufficient to make the film and scanner combination a no-contest winner over digicams in the resolution stakes.

I've seen resolutions of 100 line-pairs-per-millimeter in the centre of a B&W photographic image, diminishing to about 80 lppm in the corners. This works out to over 5000dpi in the centre, and 4000dpi at the edge. In colour, the film diminishes the resolution slightly, to perhaps 60 lppm with a film like Kodachrome, but this is still over 3000 dpi.

Desktop CCD scanners are available with resolutions of 4000 dpi, which isn't quite up to the rule-of-thumb that states you need 1.5 times the resolution of the original to get a reasonable reproduction, but in practice it's more than enough for most purposes. These 4000dpi scanners will generate files that are the equivalent of a 21 Megapixel camera! Also that's a true 21 Megapixels, e.g. 21 million RGB triads, not 21 Megapixels spread between the RGB channels. So as I said before, no contest as far as resolution goes.

Film doesn't get it all it's own way, however. Aliasing between the film grain and scanner pixels can degrade the image, as well as microscopic dust and scratches being a problem, and the film itself introduces colour errors that are added to by deficiencies in the scanner CCD. On the whole, though, Digicams have a lot of catching up to do, even to get to 35mm standards. I think Hasselblad's market is safe for a few more years yet.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 21, 2000.

Okay, I'll bite ... I have to take issue with the previous poster's answer of 21 MP. Current films are of equivalent quality to a modern pro digicam with a resolution of between 2-12MP, depending on the film. Only *very* sharp pro films (like Fuji Velvia) processed at good labs are toward the 12MP range, whereas a 2MP consumer digicam will match consumer films processed at consumer labs. Most films are probably equivalent to a 4-8MP pro camera (or an 8-16MP consumer digicam, based on current cameras).

As I've said many times elsewhere, *sure* you can scan film at 4000 DPI. You can scan it at 8000 DPI to get four times the number of pixels, or even go to 16000 DPI if you want. There's no hard limit -- you can generate whatever size file you want from film.

"But wait", you say. "There isn't 16000 DPI worth of information in film".

I answer that by saying that there isn't even 4000 DPI worth of information in film. Sure, you get more information out of it by moving up from 2000 DPI to 4000 DPI ... but four times as much? Not from the scans I've seen. Try scaling a 4000 DPI image down to 3000 DPI or even 2000 DPI, and then scale it back to 4000 DPI and see how much difference you see between that and the original 4000 DPI.

My point is that, sure, you can extract 21 million pixels from film, but they aren't necessarily particularly good pixels. A very high end pro camera, like a three-shot studio camera, might only give you 4 MP, but they are 4 million *really good* pixels. In fact, I would venture to say that a 4 MP studio camera will beat *any* 35mm film in quality because of the absolute lack of grain and flawless pixels. ("Quality" is by definition subjective, so I basically mean if you make a 16x24 enlargement from both, most people will prefer the studio camera).

Now, what about the cameras mere mortals can afford? The current crop of consumer cameras don't do too well by the same token -- the pixels they generate aren't very good, and you can scale the images down to half the number of pixels and back up and it doesn't make terribly much difference. Good pro digicams (the Kodak 5xx and 6xx and the Nikon D1) OTOH generate very, very good pixels with resolution down to a single pixel. I have made big enlargements of images from my D1, and I can promise you that there is no way on earth film is 10x the quality. Consumer digicams will hit the same image quality in a few years.

BTW, "resolution" in lab terms (like 100 LPI) just means that you can tell that two black lines are distinct. If you do this test yourself, all you'll find out is that a "line" can be awfully damn fuzzy and grainy before you can't tell it apart from its neighbor. I object to going straight from LPI to pixel measurements, because a pixel is inherently "clean" while the film at its max resolution is (basically by definition) going to be very fuzzy and grainy, and they don't handle enlargements at all the same.

Ethan

-- Ethan Nicholas (ethan@yahoo-inc.com), March 21, 2000.

Ethan, the original question was about pure resolution, not colour quality or anything else, and I did specify film of the calibre of Kodachrome. I'd still argue that practically any film, whether it's cheaply processed or not, holds a darn sight more information than a 2 Megapixel consumer digicam, especially if that digicam only outputs in JPEG format. I can tell you for a fact that there's a lot more detail on my slides than I can get off them with a 2700 dpi scanner, and users of 4000 dpi scanners will tell you that even at that resolution the slide's got a bit more to give. That's real detail, not just grain mush.

We were also talking about what's available now, not what might happen in the near future. Personally I can't wait for digicams that give me the same quality and versatility as film cameras at the same price level. For the cost of a three shot studio camera (hardly convenient, or usable for street photography) you can buy a decent SLR, a few lenses, a scanner, and a barrowload of film.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 22, 2000.

Since Ethan has thrown down the challenge: Here's a slide I picked up last night and scanned on my modest 2700dpi film-scanner. It isn't the sharpest slide that I've ever taken, it's just the first Kodachrome I picked up with some reasonable detail in it. It was taken in pretty poor light with a 24mm lens. (Can't get the equivalent of a 24mmm on your digicam? Shame!)

The whole slide

I cut and pasted the car's badge (highlighted in green, but still pretty small)out of the original and reduced the resolution to what you would get from a 2 Megapixel camera. That's here:

2 Megapixel simulation

Hmm! It's not very clear is it? Now let's see it at the original scanned resolution:

The badge, as scanned

Guess what? It's a Ferrari!

I think the pictures speak for themselves.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 23, 2000.