How to shrink an image to the ideal size without losing information?

Forum|Forum|9 years ago
December 19, 2016
1 reply
579 views

This is a problem people who use film & flatbed scanners often face, and photographers, too, sometimes: You set your image device to a high dpi setting in order not to lose any detail and end up with a file that is clearly too large. At a certain point, the higher dpi settings didn't help, and the image is composed of blobs of identical or almost identical pixels. So you want to shrink it. The problem is: How do you know how much to shrink it to get the pixel count as low as possible without losing information? The only method I've known for years was to repeatedly try it with different settings and then check the details under high magnification. It's very time consuming, frustrating, and I suspect the results aren't always ideal anyway. How about you, guys?

shrink picture

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Per Berntsen

Community Expert

As far as consumer level flatbed scanners are concerned (including the Epson Perfection series), their actual resolution is at best around 2200 ppi. So when scanning film with my Espon 4990, I use 2400. (to be on the safe side)

Professional flatbeds are a different story, my Agfa T2500 has a resolution of 2500 as advertised.

Film scanners also tend to deliver the promised resolution. I always use max resolution with my Imacon Flextight II, which is 5760 ppi for 35 mm, 3200 for 120 film and 1800 for 4x5".

R

RauPPAuthor

Known Participant

Oh, you got one of those ingenious old Agfas? They were just fantastic pieces of craftsmanship. I worked with one a couple of years ago and never found a more modern scanner of similar quality, oddly.

Per Berntsen

Community Expert

Yes the Agfa T2500 is a good scanner, and I have scanned a lot of 4x5 black & white film with it.

But it doesn't have enough resolution for 35 mm, and only barely enough for 120, and scanning roll film is also very awkward.

As far as I know there aren't any flatbeds made today that can match the quality of this scanner.

I guess the bottom fell out of the scanner market when digital cameras became common, and very few film scanners are being made nowadays. The Nikon scanners were discontinued some years ago, but the Imacons are still being made, they have been taken over by Hasselblad, and are extremely expensive. They haven't changed much optically since Imacon made them, but are much faster, since they use Firewire. My old Imacon has a SCSI connection, and takes around 15 minutes to do a full resolution scan.

An alternative method to scanning is to photograph the film with a digital camera. Larger formats would require photographing the film in sections, and then stitching the images together in Photoshop. You would need a good quality macro lens, and for larger formats some kind of rig that lets you slide the camera along the x and y axis. I've never tried it, but it should be possible to get very high quality reproductions this way.

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