Scan size and quality surprise (Epson V500)


I’VE ALWAYS ASSUMED that the quality you get from making a large scan and then downsizing it is going to be much the same as just making a small scan to start with. I now know that it isn’t.

As it takes several minutes to scan a medium format negative at 3,200lpi (with digital ICE dust removal turned on), I’ve generally preferred to use a lower resolution.

Imagine my shock, then, on discovering that the smaller scans make grain FAR, FAR worse than it really is and introduce all sorts of compression artifacts.

Here’s the proof. These scans were made from a single negative at exactly the same settings. Just the LPI was changed. To show just how huge the difference is, took screen shots at three times the “actual pixels” size of the resuling scans.

800lpi scan, at 300%:
800lpi scan at-300x

3,200lpi scan, downsized to match the dimensions of the 800lpi, then viewed at 300%
3200lpi scan downsize

And, just for comparison, here is what the original 3,200 scan looked like at 100% without enlarging:
3200lpi original crop
The scan actually looks less grainy straight out of the 3,200lpi scan at 100% than it did from the 800lpi one at 100%.

THE LESSON from this is obvious: in order to get the best quality out of the V500 (and presumably other scanners) one MUST scan big and then downsize. With a 6x6cm negative, a 3,200lpi scan means an output file of around 120MB (40MP), so to keep the memory usage under control I need to downsize all the big scans straight away.

I still can’t believe that reducing the file size increases the grain size – but it does, and I have heaps of files that need rescanning because of that.

****

As I said earlier, when scanning I always pull out the end “input” sliders in the histogram to retain all the info, rather than clipping off the whites (which the scanner does in auto mode). The Output sliders then need to go to zero and 255 to make the blacks black and the whites white. This generally creates a dull image and the midtone input slider needs to be moved down a bit to brighten it, leading to colour distortion.

This is where the midtone grey eyedropper comes in handy: activate the dropper and click it on a neutral grey part of the image and it resets the white balance. If the image is still dull, a little tweaking of the brightness and contrast sliders can help a lot – and for some reason they do not affect the “input” settings on the historgram, so they don’t add noise (which trying to adjust the input can do).

Using this method, one can get results that need very little subsequent editing, other than dealing with dust and scratches.

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About ambientimages

Paul Cowan is a former journalist turned full-time photographer.
This entry was posted in Film, Photographic techniques, Processing, Scanning and tagged , , , , , , , , , . Bookmark the permalink.

2 Responses to Scan size and quality surprise (Epson V500)

  1. Doug Morse says:

    Your conclusion is probably valid however it seems you first scan has jpeg artifacts. There may be some interactions with the grain that accentuates the lossy compression artifacts. A lossless compression scan (TIFF) might show different results. Of course if you can only make JPEG scans your conclusions are completely valid.

    • Yes, that surprised me – there was no indication that it was saving with compression but the artifacts are there anyway. At 100% they look more like very bad grain it’s when you blow them up that you see what is actually happening.

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