Digitising Photo Prints or Film

Obviously, digitising is not an issue for digital camera users. However for the rest of us we need to either scan the prints using a flatbed scanner, or scan the negatives, or ask the guys who develop your films to do the scanning (e.g. PhotoCD transfer).

Image dimensions

You should ensure that the exact pixel dimensions of your images are the same because almost all image stitching software requires the source images to be identical in size.

Scanning film yourself

By scanning negatives or slides you can get a better quality digital image than if you scan a print. But you need to be careful. Your scanner has to be high resolution because you are scanning a much smaller area than when scanning a print. Film scanners are specifically designed to scan film at high resolution - much higher resolution than most flat bed scanners.

If you have your film developed at a lab, ask the staff to be extra careful when cutting your film into sections. Alternatively ask for the film to be kept as one long strip - but ask that they do not coil the film as may get scratched.

Before scanning film, use a lint-free anti-static cloth to carefully wipe it and/or an air duster to remove dust from the surface. Both of these things can be bought from a good photographic shop. Do not use any solvent cleaning fluid.

If you look in forums and discussion groups, you will plenty of arguments about negative vs positive film. For me the key points are that (i) negative film is cheaper to buy and to process, and you can easily have prints done, (ii) positive film is easier to scan because there is less colour correction required than with negative film. Note that if you are scanning positive film it is easier (and probably faster) to scan if you do not mount the film (as if for slides). If you are using negative film you might find software such as VueScan is useful to correctly scan the film and reduce any colour correction work you have to do.

Most film scanners don't in fact allow you to scan the full film frame (i.e. 36x24mm). However, if you use a film scanner you can make a note of the actual scan area and use this to calculate the "effective" focal length of the scan (see below). If the software you use has the ability to estimate the lens settings to use for stitching by analysing your images, you should use this functionality too, in order to get the best results.

"Effective" focal length

Whenever film is scanned, whether you scan a print or you scan the negative or positive (slide) film itself, you will probably end up cropping the image area slightly. And in the case of prints, the full film area (36x24mm for 135 format) is not used for the print.

Because your scans are not of the full 36x24mm film area, the focal length you should be specifying in your image stitching software is longer than that of the lens you actually used. This is illustrated below.

cropping the scan of the negative reduces the field of view (b) of the scan, resulting in a longer "effective" focal length

Note that this illustration assumed that the scan was dead centre in the film area, which it might not be. If your scan is significantly off centre, that too may cause problems.

If you know precisely how much of the film area was cropped, and providing your scans were dead centre, you can calculate the "effective" focal length using the lens calculator.

Image Registration

When scanning images "image registration" means the accuracy with which you scan the original image. So good image registration means that you are careful:

  • the image is scanned square (in other words the edge of the scan area must be perfectly parallel with the edge of the original image)
  • the centre of the scanned image exactly matches the centre of the original image

Neither of these can be guaranteed if you scan from prints or if you use a film scanner that does not scan the full 135 format frame (36x24mm). Instead the best option is to scan film using a flat bed scanner in long strips and then carefully rotate the scan as necessary until the edges of the images are straight. You can then cut out the photos.

Photo prints

Most photo developing labs use mass-developing machines that can process lots of films very quickly. In order to make this possible one of the things these machines do is that they develop only the centre part of the negative - a small amount of the edge is lost. If you have ever taken a picture of someone using an SLR camera, had them developed, and then wondered why the person seems to be cut off at the ankles... this is it.

If the lab you use allows you to give special instructions, I suggest:

  • Please use the same settings for colour/contrast and brightness on all images
  • Please fix the location of the cropping frame so that all images are cropped in the same position (preferably at image centre)

PhotoCD services

Most photo processing labs now offer a service to put your photos onto a PhotoCD. This may involve sending your negatives or slides away to another lab where the scanning is done. All this means that someone else has to do all the work of cleaning your film and carefully scanning it, including adjusting colours. However if you take your photography seriously, make sure you ask exactly what level of service you will get including what resolution scans you will get on the CD. Not all "PhotoCD" services are the same.

Some labs allow you to provide special instructions. If so:

  • Please use the same settings for colour/contrast and brightness on all images
  • Image registration is important for the customer's intended use of these images

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