Hi,

Just want to get a feeling on how good todays digital camera are ? From the film scanner reviews, it seems that negative film must have a resolution around 2500dpi or so(and positive I believe would be even greater?).

If that is the case, how can the trade press said that a 2M pixel DC is approaching conventional film cameras ? A standard 35mm(24mm x 36mm) have much more 'pixels' than 2M.

Gary

-- Gary Ng (gng@extracomm.com), February 22, 1999

Answers

It obviously depends heavily on the film type, but it's generally accepted that film is somewhere around 6 million pixels of resolution. It depends a lot on what you mean "equivalent" or "approaching": Megapixel-plus digicams can produce prints at 4x6 or even 5x7 size that are almost impossible to tell from true photo prints. The 2 megapixel units may go even larger. Blow any of them up to 16x20 though, and you'd certainly see a difference relative to fine-grained film!

-- Dave Etchells (web@imaging-resource.com), February 25, 1999.

It depends upon 1) the film's graininess and 2) The sharpness, or resolving power of the lens.

A very good commercially available lens can typically resolve around 70 - 100 lines per millimeter, so 35 mm would top out at roughly 2400 x 3600 "pixel equivalents" on 35 mm format film, which would be around 8 million pixels, with 4-6 million pixels being more typical. A very fine grain film (such as Kodachrome or Fuji Velvia) will be able to resolve enough to generally max out the capability of pretty much any lens. Faster films, like ISO 400 speed or greater, are grainier, and the effective resolution from a 35 mm might be more like 2 million pixels. Some specialized applications may value low light sensitivity above anything else (typically these films that are push processed to ISO 1200 or more), and these films are granier yet (the longer processing times makes the silver crystals in the film, or "grain" grow even larger). With these film/processing combinations, the effective resolution might be no more than a megapixel from a 35 mm frame.

-- Doug Green (dougjgreen@yahoo.com), February 26, 1999.

If you're trying to compare digital resolution to film.... divide the digital pixel count by 3. Why? Because each "pixel" on a digital camera only does one color. On a typical one megapixel camera, 250,000 will be red, 250,000 blue, 500,000 green. (You'd think it'd be the same ratio, but no) The camera does some color interpolation to arrive at the max resolutions they deliver. Depressing, isn't it?

-- Benoit (foo@bar.com), February 26, 1999.

Hi,

Thank you for all the answers which taught me a lot. Seems that I better stick with my good old FM2 and invest into a 'professional' film scanner instead. It is cheaper, lighter on the road and give me superior quality.

Gary

-- Gary Ng (gng@extracomm.com), February 26, 1999.

I would like to make a correction to the answer that Doug Green gave.

If you want to equate 100 lines per mm (which an extremely good lens/film combination can achieve) with the corresponding number of pixels per mm, you have to remember that it takes twice as many pixels per mm to resolve a number of line pairs per mm. So 100 lpmm requires 200 px/mm, so you get:

24mm x 36mm would top out at roughly 4800 x 7200, which would take about 35 Mpx.

That is a lot!! Half that resolution might be more "average", resulting in about 9 Mpx. That corresponds to about 50 lines/mm. Depth of field markings on lenses correspond to about 30-40 lines per mm, but unsharp components in a chain add up, so if you have a film or CCD of also 30-40 lines/mm, the net result will be much less. Therefore, I think 50 lines/mm is the minimum film/CCD resolution for high quality. 9Mpx is still a lot more than present digital cameras, but perhaps "reachable" within a few years?

The mentioned number of pixels are full rgb-pixels, whereas a camera CCD has only 25% red, 25% blue, and 50% green. After som digital processing, the luminance resolution is about what corresponds to the number of pixels, whereas the chromatic resolution is less. So a 9Mpx camera will not be as good as a 9Mpx scanner.

Regards, /Harald

-- Harald Brandt (heb@algonet.se), October 11, 1999.