Stacking Multiple Scans of slides

Chris Pickford · Post by **Chris Pickford** » Thu Nov 29, 2007 1:24 pm

Somewhere out there, I'm sure that there are still a few old fogeys like me who still use slide film (as well as a DSLR). I have a relatively low resolution slide scanner (2400 dpi) which gives good, but not brilliant scans compared with the original slide.

Rumour has it that, if you scan a slide a few times out of register (ie taking the slide out of the holder each time and replacing it) and combine the scans in Photoshop you can effectively increase the resolution of the resultant scan (eg, 4 scans combined would effectively double the resolution to 4800 dpi).

Has anyone tried it? Any advice to offer?

I'm trying to get a better result than I do with a simple scan (see below) which is ok, but not brilliant.
Chris

Jack Harrison · Post by **Jack Harrison** » Mon Dec 10, 2007 6:41 pm

That technique sounds very akin to the use of an unsharp mask.

Rather than taking four (or more) scans of the slide, one not make one and then copy but make the register very slightly different (one pixel) so you can add the two images? I am about to try with some pictures and see what happens.

Jack

Post by **Padfield** » Mon Dec 10, 2007 9:09 pm

I've used free stacking software from the internet to improve pictures taken as videos down my crummy cheap telescope. Both the telescope and the webcam I pointed down it introduced obtrusive artefacts but the software eliminated them all because they were in a different place in each frame. The software was designed for specifically for videos: the object glides through the field of vision as the sky (or rather the earth) turns, then the software takes all the frames, matches them up and produces a composite. But I can well imagine it working with a smaller number of scans. Here is a sample result:

Guy

Post by **Padfield** » Mon Dec 10, 2007 9:17 pm

I've just checked and the software I used is called RegiStax, available at http://www.astronomie.be/registax/.

I've never used Photoshop so I've no idea if that can do everything RegiStax can do.

Guy

Jack Harrison · Post by **Jack Harrison** » Tue Dec 11, 2007 7:39 am

I am vaguely familiar with the principle of stacking images and the results on astro photography can be very impressive indeed. Here is a very good example:
http://www.cs.unm.edu/~kwiley/software/ ... acker.html

If I understand correctly, stacking astro images requires that a lot of identical images are taken of the same object. Clearly this is not possible with a live butterfly. So what we are talking about here is the equivalent from one image that has been processed in several different ways - eg stacking of images where some are blurred, some have Jpeg artifacts, etc. Averaging out all these imperfections (artificially added in this case) might produce an apparently sharper image but my preliminary experiments are inconclusive.

I had a quick fiddle with you Moon shot Guy and in Paint Shop Pro, the "Clarify" tool improved things considerably. I have both Paint Shop Pro (came free with cornflakes) and the cheapest £22 Photo Shop Elements. I find they both have their uses.

Jack

Chris Pickford · Post by **Chris Pickford** » Tue Dec 11, 2007 3:56 pm

Thanks for this. I've used RegiStax for astro images of planets (another hobby), but there are size limitations for files, although it certainly helps where there are less sharp areas in images.

What I had in mind was the kind of thing that the next generation of DSLRs are said to be likely to incorporate - you press the button, and a series of pics are taken in quick succession with the sensor moved slightly each time so the the stacked image has a very high effective pixel count.

I had heard that there were folks out there doing it with scanned images (hence the message above). I have tried it, but my PC is not man enough for the task - I was hoping that someone with a serious desktop and more PhotoShop skills than I have could give some hints.....