60MP from 6x7 Film

120 Provia 100F

This image was taken with a Mamiya 7II, 80mm lens, at f/16.  It's a high-contrast subject, so makes for a good test image to determine maximum practical resolution.  For those who are unfamiliar with this camera, it's a 6x7 medium format rangefinder with interchangable lenses, that takes 120 or 220 roll film.   To find the resolution, I scanned a 24x36 portion of the image at 5760 ppi in an Imacon Flextight Precision-II scanner.  The flexible holders used in this scanner permit making high-resolution crop scans by simply loading loading film in a smaller-format holder.

In my previous 11MP from 35mm Film test, I used NeatImage to reduce the grain.  I didn't do that this time; instead the crops shown are straight from the scanner.  I also didn't spot the file.  It has been suggested that NeatImage affected fine detail in the 35mm test, so I thought I'd leave it out this time.  Instead, later in this test I'll add a separate section to confirm that NeatImage doesn't negatively affect image content when applied to a sufficiently high-resolution scan.

Full frame overview

The crop below is the highlighted (blue) area above.  The first crop is the full-size scan and represents a 200MP file at 5760 ppi.  The others were derived by downsampling the full-size crop scan.
200MP
127MP
97MP
71MP
60MP


3200ppi Scan Resolution

The scan above was made and downsized from 5760 ppi.  Scanning medium format (120 strip, up to 6x20) my Imacon scanner can "only" scan at 3200 ppi.  Curiously, 60MP represents almost exactly this resolution!  It corresponds to about 50 lp/mm.  At 3200 ppi the CCD head is higher off the film, and the illuminant relatively narrower within the optical view of the head.  This results in higher dynamic range and generally better scans.   Here's a crop of the same area from a 3200 ppi scan.  I've repeated the downsized version from above side-by-side for comparison.

3200 ppi 60MP

Note that this is straight from the scanner.  Rotation may be slightly different since it was scanned in a different holder.  Looks the same to me in terms of detail.  Color and and general tone is a little better.  The 35mm crop scan is a little higher contrast and may appear slightly sharper for this reason.  The 3200ppi version can always have the contrast increase though.  Overall, nothing is lost, which is what I wanted to verify with this test.

NeatImage

Here's the same 5760 ppi scan downsampled to 60MP.  Only this time I used NeatImage to reduce the grain before downsampling.  The two variants are side by side with the NeatImage version to the left.


NeatImage (60MP) 60MP

Looks the same to me, exception the left image is a bit cleaner, although it's not obvious what in the right image is actually grain noise and what's texture.  This shows that in some types of images the grain of Provia 100F is a non-issue.

Conclusions

  • See also 11MP from 35mm Film.
  • Both my Canon EOS 35mm and Mamiya 7II 6x7 frames, although I use them for different purposes, contain about 50lp/mm, or about 3000 ppi worth of image content.  For 35mm this translates to 11MP.  For 6x7, it's 60MP.
  • Realistically, a 645 frame should contain about 4.5/7ths of the 6x7 frame, or just shy of 40MP.
  • I shoot 6x7 as a lightweight, portable, alternative to 4x5 for landscape photography.   This is quite feasible when print size expectations are moderate, a fine-grain film is used, subject is reasonable contrast, lenses are used in the f/8-f/16 range, and no movements are required.  If I know I'm going to need a really big print, use movements, or shoot on HP5+, 6x7 is not a viable alternative to 4x5.
  • I don't spend too much effort ekeing out the last 10%; that's when it's time to move up in format.  The exception is long lenses on 35mm, where moving up in format isn't an option.
  • 60MP is 6900x8700.  At 240 ppi it permits a roughly 29x36" print.  This is more than my Epson 7600 can do.  At 300 ppi it's 23x29", which is a good fit.   To see how I came up with 240 ppi, see my Epson 7600 Resolution Test.
  • 6x7, for me, is perfect to drive my Epson 7600 with a little margin to trim and make minor crops.  It's a little short for bigger prints, such as those produced by the Epson 9600.

Jan Brittenson <bson@rockgarden.net>            7/4/2003