While statistics would suggest that most of us take photos using digital cameras, that hasn’t always been the case. Somewhere in your home you probably have piles of slides, negatives and other images that you would use and share if they were in a digital format. So, how do you convert older images into digital files so you can use them? This month I’ll explain the basics of converting these files.
The procedures for scanning slides, negatives and processed photos are all different. Processed photos are printed on paper and they’re opaque, while slides are transparent. In addition, when you hold a slide up to the light it’s pretty easy to see what the picture is about as it’s a positive print, albeit a small one. Negatives are similar in transparency to slides, but hold a negative up to the light and it is harder to see what the subject of the image is – the colours are not only reversed but they are also covered with a yellow/ orange colour cast.
These differences in opacity, colour and colour cast make the process of scanning processed images, slides and negatives very different. Most scanners can handle scanning photos, but not all can scan transparencies such as slides and negatives. To handle scanning a transparent item a scanner must have a light source positioned above the image – in a regular flatbed scanner this necessitates a second light source in the lid. The light in the bed of the scanner is used for reflective objects like photos and the light source in the lid is used for transparent objects like film negatives and slides.
Many of today’s scanners have a second light in the lid and can scan slides and negatives. This light is generally hidden under a removable pad in the scanner lid – it’s left in place when scanning photos but must be removed when scanning transparent objects such as slides and negatives. When it is removed, you can place your negatives or slides on the scanner bed to scan them. Many scanners also come with removable plastic templates that you lay on the scanner bed and which provide ‘slots’ into which you can place slides or negatives. These are handy because, when a scanner has these templates available, you’ll generally be able to scan multiple slides or negatives at a time and the software will create separate files for each.
The scanner software will also take care of removing the colour cast from the scanned negative image and inverting the colours, so that what you end up with is a positive image from a film negative. To ensure your scanner knows what you’re scanning and so it can make the required changes to the image, use the scanner software to perform the scan and not a generic tool like the Windows Scanner and Camera Wizard – it won’t have the flexibility and complexity of your scanner’s own software.
When scanning negatives and slides, resolution is important. For a photo, to use it at approximately its current size you will scan it at around 300 dpi. If you need to make the image bigger, a scan of 600 dpi is usually sufficient.
Slides, on the other hand, are generally very small – being less than 2.5cm in dimensions. In most cases you’ll want to use the scanned image at a much larger size than this, so you’ll need to ensure you scan at a high resolution so you have enough image data to use for your intended purpose. Typically, making a slide scan at 2400 x 2400 resolution or above is required and your scanner should not be interpolating at this resolution; that is, it shouldn’t be guessing intermediate values because it can only really scan at 1200 x 1200 dpi.
Your scanner software may or may not immediately distinguish between a photo and a slide or negative and if it doesn’t, look for some advanced scanning options which let you configure it for the best results. These include selecting the type of document and the resolution. In addition, if your scanner defaults to scanning an entire A4 size page, avoid accepting the default scanning area or you’ll end up with enormous files, only a small amount of which is actual useful image area. Instead, make a preview scan and then use the selection tool to select around the area to scan before making the scan. Later, when you return to scanning a regular document, set the resolution to a more acceptable value or you’ll end up with everything being scanned at too high a resolution.
Other options for scanning slides and negatives include purchasing a separate transparency adaptor for your scanner. This replaces the scanner lid with a larger lid with a separate light source to shine light through the transparency, so the scan can be made. Check to see if your scanner has a transparency adaptor available for it.
Another factor that affects the quality of the results if you’re a purist is the density of the image, which is a measure of the image’s contrast range. This is lower for a photo and higher for a slide, so you’ll need a scanner which can handle the higher dynamic range that will be found in a slide. If your scanner hasn’t the ability to handle this range, you’ll get some clipping of values in the darker areas of a slide and, conversely, in the lighter area of a negative.
In addition to scanners that can scan a range of media, there are also dedicated slide scanners that can process slides in a more efficient manner. Some allow you to preload a series of slides and then set the scanner to run, and come back later to review the finished scans. If you’re a purist, these scanners can achieve much better results than regular scanners, as they have no glass between the slide and the scanning sensor, so you can avoid problems such as those caused by marks or scratches on the scanner glass.