Tue, 19 Oct 2010

Digitising Slides

Sliding past expensive equipment to digitise slides

The Problem

I had around 300 old family-slides laying around. Most, if not all of them, from the 60s. They were stored less than optimal and while most of them had a green tint only, others turned completely yellow or red. Because those slides take up quite some space (including the projector) and no one uses that thing anyway it was time to get rid of them. However, not without storing that historic information on something smaller, like a DVD.

Possible solutions

  • Film scanner: Most of those include digital ICE which should produce very acceptable results. But they are pricey and 300 slides (that are primarily of sentimental, if any, value) don’t justify any expense higher than 0€.
  • Flatbed scanner: Why not use my old Canon FB630U? I write “old” because there are no drivers for Windows 7 or a current version of Mac OS X and it doesn’t work with SANE. So I got rid of Ubuntu on my notebook and installed Windows XP to be able to use that archaic, incredibly slow scanner again. After scanning a slide, which included finding the right amount of light for the back-lighting, I realized that there is nearly no depth of field and 600dpi for a slide is not necessarily excessive.
  • Digital camera: Do what others do in a similar situation: use a digital camera to photograph the slides while back-lighting them. The advantage of this approach - when it comes to back-lighting - is, that I don’t have to change the lighting condition but can set the right exposure on the camera. So the decision was made.

Doing It

Hold me

After I settled on the method, I needed some pratical apparatus to make the whole thing as painless as possible. Because I knew that I’m not going to shoot all slides in one go, I needed a solution that I can put away in-between and use again within no time. By taking a wooden stick and attaching it to the camera’s tripod mount I had the basis for my construction.

Picture of the contraption

Next thing I needed was a way to hold the slide in place and for that I took a thick cardboard of which I took two layers to raise the slide above the wooden stick and into the middle of the frame. Add to other layers of that on the front and the back, distanced so that a slide fits perfectly in between and you have a very cheap but working holder for the slide.

Thrill me

The next choice I had to make, was the lens I would be using. Because of the limited length and the resulting small focusing distance I’d have needed a macro lens. Unfortunately I don’t have one (often thought about getting an EF-S 60mm, but I could never convince myself to spend the money on it, which was no different this time), so I stuck with the EF 24-105 f/4 which has the biggest magnification of my lenses. That said, I still had to use it at its MFD, which is never a good thing to do, but I was limited by the sticks length and the fact that moving the slide further away reduces the effective resolution of the slide because it becomes smaller. Anyway, gotta use what you’ve got!

Kiss me

With all of that out of the way it came to the actual shooting. I positioned the whole thing so that the background of the slide was a bright (preferable white) background. Because the distance between the slide and the wall was about 1m it was out of focus anyway and any fine pattern on the surface didn’t matter. At the end I used ISO 200 (ISO 100 on a 50D doesn’t make much of a difference in noise) @f/8 (to be at the sweet spot of the lens in regards to aperture, as I’m already stuck at the MFD) and 1/100th of a second. To reduce any further blurriness because of vibrations I used a cable release to trigger the mirror-lockup and the 2s self-release timer.

And that was basically all1 there is to it. Take a slide. Put it between the two cardboard layers. Press the button on the cable-release. Wait. Remove slide. Rinse and repeat. One slide took me less than 10s.

Kill me

What then? Well, first of all, crop and level the images. Those slides where only 1/3 of the full image-frame. And levelling was very important, because whoever took those shots in the first place, had problems with level pictures to start with :) I did not sharpen them while converting them from RAW to 16bit TIFFs. I also did not change the white balance. Those slides were all over the place when it comes to colouration anyway.

When I first saw the pictures on screen I was disappointed because they were so blurry, until I came across 2 slides from 5 years ago. Those were very sharp. With a sigh of relief I accepted that it was not my method of digitising them, but the original slides that were not sharp at all. Finally I loaded them into Photoshop and used Level to give them back their original colours by setting the grey point. Also compressing by moving the black and white point to where they belong. On the rare occasion where that resulted in a slightly bluish tint, I used Color Balance to remove it.

All was fine at this point, except their sharpness. So I reduced them in size using Bicubic Sharper. Because my target device is a digital picture frame supporting a resolution of 800x600 pixels only, I resized the pictures to 800x533 and applied Unsharpen Mask (100%/0.3/1).

Example of a finished slide

Now, are they good looking and sharp pictures? Nope, but at least they cannot degrade any further, don’t have any colour shifts and take up much less space. I consider that to be a victory.

  1. The really time-consuming thing was to physically clean up the slides. That took way more than 10s per slide. [return]

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