resolution of digital vs. 35mm

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Hi,

I enjoyed the digital camera reviews found at this site. I liked the imaging of the test patterns. I noticed that the Nikon 900 resolves about 750 lines across an image.

This got me wondering what the resolutions of various 35mm slides and negatives are. I remember reading long ago that some high-quality very slow films have photo-sites that are about 2-microns wide giving and equivalent digital camera pixel density of about 12,000 dpi (drawing a somewhat flawed analogy between a CCD pixel and an emulsion photo-site.

Obviously, the spatial frequency of resolved things (like lines and test patterns) is lower than this density.

If we were to point a typical SLR 35mm camera at the test patterns used in the digital camera reviews, what kinds of resolutions would we see?

Thanks much,

swest

-- Steve West (swest@as.arizona.edu), September 04, 1998

Answers

Excellent question!

It's generally accepted that "typical" 35mm color film resolution is somewhere around 2Kx3K pixels, and that's the reason Kodak chose that resolution as their highest res for standard PhotoCD. In practice, with any reasonably fine-grained film, you're more likely to be limited by lens performance and camera shake than the film itself. 2 micron resolution at the film plane is *way* beyond what even very high-quality 35mm camera lenses will deliver.

As it happens, I've shot some of the targets in the test with very high-res film for use in our scanner testing (which you'll be seeing much more of shortly). The original for the "house" poster was shot on Kodak Royal Gold 25 film, which is *extremely* fine-grained, although the lens that took it had some corner-sharpness problems. The upper-central portion of that shot makes a great resolution test, looking at the leaves & pine-needles against the sky. I have that image scanned via Pro Photo CD (4K x 6K pixels), and will try to get around to posting a clip of it under the scanner area in the next weeks, as a comparison. I currently have the res target shot on Kodak Gold 100, which is quite fine-grained, and am about to shoot it on Kodak Technical Pan (extremely high-res B&W film). I'll also try to post super-res scan clips of those as well, for comparison. (But don't hold your breath - I just got a large consulting contract that will keep me crazy-busy for the month of September, plus have the new Nikon scanners to test, plus expect at least two new camera models to arrive for testing in the same time frame...)

-- Dave Etchells (web@imaging-resource.com), September 10, 1998.


Dave,

Thanks for the response. I'm starting to get lost with dimensions now, so let me try to summarize in pixels/mm in order to compare apples and apples.

Let's suppose that a typical digicam CCD is 1/2" wide x 1280 pixels. This gives about 101 pix/mm. I'm not sure about the dimensions of a 35mm rectangular negative. I'll just assume that the 3K is across 35mm and not something longer. That gives about 85 pix/mm.

If my estimate holds, digicams are starting to beat 35mm film in raw resolution. Is this your conclusion or did I screw something up?

thanks again :)

swest

-- Steve West (swest@as.arizona.edu), September 10, 1998.


Actually, the biggest CCDs common these days in digicams are 1/2 inch on the diagonal, not across. Anyway, the resolution issue isn't how big the pictures are on the sensor, but how many pixels the entire image is divided up into. (Another way of looking at it is how big would each pixel be once both the 35mm film and digital image were blown up to 8x12 or whatever.) The short answer is that low-end digicams aren't yet anywhere near the best 35mm film, but the best of them are actually pretty close to the performance of typical film in a typical $100 point & shoot (only the digicams cost $1,000). High-end professional digicams like the Kodak DCS 560 get pretty doggone close to 35mm. High-end studio digicams that use scanning backs (like the Dicomed or Phase One) routinely blow away even 4x5 film. For most people, I suspect that digicams with 3 megapixel or higher sensors will be "good enough" to completely replace film in routine use. My guess is we'll have devices in that ballpark by the end of 1999, or early 2000, but they'll still be pricey. (The 1.5 megapixel units of today by contrast will be under $300 by that time frame.)

-- Dave Etchells (hotnews@imaging-resource.com), September 10, 1998.

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