The Art and the Science of Scanning Slides and Film

The Process

Scanning of slides and film is NOT a straightforward automated process. I do not feed a hundred slides into a machine, press a button and come back an hour later.

Each slide is looked at individually and decisions are made as to how to process it.

I will give each slide a gentle brushing to remove any dust and put it through the scanner using a resolution of 2000 dots per inch (dpi). With a first-rate slide this may well produce a satisfactory result. However it is surprising how often there is ingrained dust or other marks that I cannot physically clean. In that case I will use an infra-red system known as ICE4. What this does is take an infra-red picture of the imperfections and subtract that from the main image. This will often produce a striking improvement. There are then other technologies that recognise the film type and make consequent adjustments affecting colours, fading and grain.

image 1 showing dust image 1 showing dust removed
a not uncommon scattering of dust the result of cleaning using Digital ICE

After that I have another look at the picture. I will consider whether some careful minimal digital adjustments could improve the image of a sound slide. Now I'm sure that your slides (like mine!) are all perfectly exposed but sometimes I come across a customer's slides that could actually benefit from a slight adjustment to the colour balance or the light/dark balance etc. I will not be doing any air-brushing-type 'improvements'. I will remove as far as possible any surface dust or marks that were not removed by Digital ICE. I will fix any 'Red Eye' problems. I will fix any obtrusive grain problems as far as possible. But if your slide is out-of-focus the digital image will be the same. Please note that this is not intended to be a digital restoration service. Sometimes slides have deteriorated such that there are blemishes over an extensive area. In this case the digital image will simply be a faithful copy of the original, warts and all.

image 3 showing poor colour. image 3 showing improved colour.
Is there anybody there? A dreadfully underexposed low-light slide The result of digital adjustment: not a perfect picture but the owner was very pleased to see it.
image 3 showing purple cast. image 3 showing with cast removed.
Better after Digital Ice cleaning. But there's a
definite colour cast.
Colour cast corrected.

After these adjustments, I save the file as a TIFF file. TIFF is the pre-eminent format for image files and is 'lossless' - however many times they are edited there is no loss of detail. The TIFF files are large - generally around 14 MB and are not intended for daily use. It is common practice to save space on the disk by compressing the file losslessly using LZW compression. However as this is a proprietary compression format it cannot really be expected to be usable in the very long term and I do not use it. If you have requested TIFF files these are now written to disk. When you receive this disk please check that the disk is OK and readable before putting it away. Let me know at this stage if there are any problems.

Finally I convert the images to JPG files. JPG is the commonest format used in digital cameras. (The filename has the extension '.jpg') These files are on average 750 KB. It is these files that are then put onto you main CD/DVD for copying onto your computer.

One more possible action is the addition of invisible captions to your jpg files.
Many customers have captions for their slides either written on the slides or in the lid of a slidebox. Once slides are scanned you will normally lose those captions. But they can be very important. If they are in the lid I would recommend that you take a photo of the lid and then include that with your jpg files. This will only be foolproof if the numbering of the jpg files matches the numbering on the lid. Another way of dealing with captions is embedding them in the jpg files. Technically speaking the captions are held in the IPTC field 'description' and most photo viewing software will have the option of seeing the caption along with the picture. I think Picasa caters for this. (Can some kind Picasa user confirm this?) Irfanview certainly does. If you use Windows it is possible in Windows Explorer to see your list of files with the captions next to the filename. I can discuss this with you if you enquire about captions.
I will only be able to embed captions if you can provide:
  • slides individually numbered
  • a list of captions in a text file with slide number and caption, which must match the number on the slides.
I do not undertake to try to use any handwritten list of captions.

The resulting images will have a resolution of approx 2660 x 1820 pixels with a filesize varying between 500 KB and 1.0 MB. This will easily allow prints to be made up to A4 size. This would usually be satisfactory for most purposes. This is the resolution that I have used for my own collection of several thousand slides.

The Maths

Here's the maths. The 35mm film slide picture area is 36mm x 24mm. 36mm is 1.417 inches. Scanning at 2000dpi will produce 2834 dots so you end up with an image 2834 x 1890; 2834 x 1890 is equivalent to an image from a 5.4 megapixel digital camera. Your computer screen might have a resolution of 1024 x 768 pixels. Its maximum resolution is likely to be around 1280 x 1024 so your picture is about twice as big as your computer screen measuring linearly, or four times as big in area. Now what's the point of having a picture four times bigger than your computer screen? Well none at all really if all you want to do with it is look at it on a computer screen. But if ever you want to print the picture you'll need that extra detail. And if you want to trim the edges off a picture to home in on a particular part of it, then you have some leeway to do this. To see the printing capabilities of this size of image, there is a useful online megapixel calculator. In practice I find that the size of the picture in mounted slides is usually slightly less than 36mm x 24mm, so the actual filesizes and dimensions will be somewhat less than calculated here.

Professional customers who need to produce very large artwork and therefore require a higher resolution scan should approach a specialist company who regularly meet this requirement. A scan at 4000dpi produces TIFF files of 60MB or 120MB depending on colour depth chosen, and I do not offer this facility.

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Terms and conditions

  1. I can only accept orders from within the United Kingdom.
  2. I shall always take great care of your property. However I cannot be held responsible for any failure by the postal services. If you send a package to me that never arrives, you should make your own representation to the postal service.
  3. It is assumed that the customer holds the copyright of all photographs. I will process the slides as presented to me and cannot be held responsible for any breach of copyright.
  4. Your privacy is paramount. Your personal details will never be divulged to any third party. Likewise your photographs are kept strictly private and will not be made available to any third party.
  5. I shall give the slides a light and careful brushing prior to scanning, but I do not provide a cleaning or repair service. Proper cleaning, wet or dry, of photographic material is a specialist service that I do not provide. Also any slide that is falling apart cannot safely be put in the scanner. If I find the occasional slide that is coming apart I will remount it in a plastic frame but I can give no warranty for this extra work. (Basically I would not wish to disappoint a customer who may well not have noticed the odd bad slide-frame). But I will not undertake to do wholesale repairs on batches of slide-frames that have deteriorated.
  6. Please accept that it can at times be almost impossible to be sure of the orientation of any particular slide. Once scanned, individual photographs can very easily be reoriented within your computer. See 'Flipping Images' on the Order page.
  7. The slides will be scanned to the highest standard, but no warranty can be given regarding the appearance on any particular computer. Computer screens vary greatly in lightness and darkness etc. Also remember that if your original photo was not sharp, the scanned version will not be sharp either.
  8. I do not guarantee that the slides will be returned in exactly the same order/orientation. If they were all ready for projection please be prepared to go through them again if you want to project them.
  9. Slides in glass mounts can cause scanning problems such as Newtons Rings. If you present me with slides in clip-on glass mounts I may have to remount them. If I do this I won't be putting them back in their glass mounts.

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