Scanning Old Photos for Printing

Plenty of photographers have boxes of old negatives, slides and prints they would like to digitise to make them more accessible. But many are put off by the complexity of the process and the amount of time it takes to scan, restore and catalogue old pictures.

In this feature we’ll look at what makes a suitable scanner and which resolutions you should use. We’ll also provide a few tips on rectifying the most common types of damage that occurs to old photos

Scanner Choices

Unless you’re assembling a collection of images for printing larger than A2 size (420 x 594mm) you don’t need a top-of-the-line scanner. The main factor to consider is the type(s) of originals you want to scan. If you only have prints, a simple flatbed A4 scanner will do the job and most will support high enough resolution to produce images that can be printed at A4 size – or larger.

If you have a mixture of prints, negatives and slides you will need a scanner with film holders.

A mixture of prints, negatives and slides will narrow your choice to scanners with film holders. Scanners with 35mm format film holders are usually cheaper than those equipped to scan larger format films. Most regular scanners can scan prints up to A4 or ‘letter’ size (8.5 x 11 inch / 21.6 x 27.9cm)

Larger originals need to be scanned section-by-section as A3 scanners are very expensive. You require a scanner with minimal difference in height between the raised lip around the glass and the platen. Simply butt the corners of the oversize photo or poster to each corner of the platen in turn and make the required number of scans. Allow some overlap area for stitching the scans together with editing software.

Scanner Attributes

If you look at scanner specifications you will find details of the following attributes, all of which can affect scanner performance.

1. Dmax. This represents the maximum density at which shadow detail can be distinguished and provides a good guide to the dynamic range the scanner can handle. Even low-grade scanners offer at least 2.5 Dmax, which is fine for reflective originals (documents and prints). To scan film you need a Dmax of about 4.

2. Colour Depth. This specifies the number of bits captured per pixel, which is related to the number of possible colours the scanner can record. Typical bit depths are 24-, 32-, 36-, 42- and 48-bit. Look for high bit depth if you have colour originals to scan.

3. Optical Resolution. This is the actual number of pixels the scanner can provide. Scanners typically quote two figures for optical resolution; the first representing the number of sensors in the scanning array and the second the number of steps the array is moved in as it traverses the platen. Both numbers are in pixels per inch (ppi). If a scanner has a resolution of 4800 x 9600 there are 4800 pixels/inch in the scanner array and the array steps through 9600 lines/inch.

4. Interpolated Resolution. Also termed ‘optimised resolution’ this indicates the ability of the scanner software to ‘fill-in’ spaces between scanned dots. It’s important if you plan to enlarge images for printing or when scanning film frames for archiving. Most scanners should offer an interpolated resolution of about 9600 x 9600 dpi.

5. Scanning Speed. Scan speed is typically rated in pages per minute (ppm) and based on scanning office documents. Photos generally take longer to scan at high resolution, so you must balance the need for speed (for high-volume scanning) against the desire for quality.

Preparing Originals

Original negatives are preferable to prints because they are less prone to fading and loss of resolution and they retain a wider dynamic range. Use a very soft brush and compressed air blower to clean them.

There’s only so much you can do to repair physical damage. In some cases, torn prints can be repaired for scanning by applying tape to the back of the print to hold the pieces together. Negatives that have been cut are more difficult to repair After that, you must rely on image editing.

Settings

Automatic settings can be useful for novices and provide a convenient shortcut. But they may not scan at the resolution you require. Decide how the scans will be used. Different usages have different scanning requirements.

If you can’t decide – or when scanning simply to archive your pictures – opt for a high resolution that will support printing at a minimum A4 size. Many scanners provide aids that help you set the correct scanning resolution. The table below shows optimal sizes and scanning resolutions for different outputs.

Application	Ideal Image Size (in pixels)	Resolution (in pixels/inch)
For mobile phones and tablet computers:	1024 x 768 pixels	72 ppi
Viewing on widescreen TV sets:	1920 x 1080 pixels	72 ppi
Printing up to snapshot size (15 x 10 cm)	2000 pixels wide	300 ppi
Printing to A4 size	4000 pixels wide	300 ppi
Printing A3 and A3+ size	4500-5500 pixels wide	200-300 ppi

B&W originals can be scanned with either the colour or the greyscale mode. The colour mode collects more data, giving you  more flexibility to manipulate the image. You can change it back to greyscale after scanning. Sepia-toned originals should always be scanned in colour.

Make sure the source mode you select matches the original. Pictures or articles in books and newspapers must be de-screened and pre-sets are available in many scanners. Always ‘preview’ or ‘pre-scan’ to check what the end result will looks like before committing to a scan.

Drop-down menus in the driver interfaces of most scanners allow users to match the scanning parameters to the original image, even in the Basic mode.

Scanning Tools

Most modern scanners come with software tools for removing common blemishes like dust spots and scratches, and correcting faded colours. They are usually found in the scanner driver. Because they are automated, they may not ‘work’ with every image you scan and they invariably increase scanning times, often by a minute/scan or more.

The preview scan (left side) may not look anything like the end result you want but most scanner drivers provide tools for tweaking brightness, contrast and sharpness and removing dust and scratches to produce the end result shown on the right hand side of this illustration.

The most common tools are as follows:

Dust and Scratch Removal. In most cases, the tool only works with film-based originals. It requires two light sources: one which records data from the red, green and blue channels plus an infrared (IR) lamp. The film is scanned twice, once with each lamp. The IR lamp detects the dust locations, which are mathematically subtracted  from the RGB image.

Before and after screen grabs showing the effect of infrared-based dust and scratch detection and removal processing.

Colour Restoration. These tools ‘read’ the dye signature in the base layer of the scanned colour film and use the information to rebuild the original colour values. This process is more accurate than post-scan software that attempts to guess how the original colours and tones would appear.

Grain Management. This tool collects information about image grain during a scan and combines it with information on sharpness and colour in order to reduce the visibility of grain in the final image. Some softening of the image may occur.

In most cases, these automated tools will provide a noticeable improvement to the original, although further editing may be required to remove all blemishes from scanned images.

De-screening. This tool is used for removing the dot-screening from originals that come from newspapers and magazines.

Sharpening. Raw scans are always a little soft because scanners work by sampling the image data and averaging values. This tends to reduce contrast and smooth the image. Most scanners include settings for Unsharp Masking, a popular way to apply sharpening to a scan.

The Unsharp Masking dialog box should contain adjustments for Amount/Intensity, Threshold and Radius, which let you specify the amount of brightness to add to edge pixels, the brightness difference for defining an edge, and how wide a border will be affected.

Some of the adjustment tools for tweaking image brightness and contrast.

Editing Tools

Almost all image editors provide tools for repairing blemishes that can’t be fixed at the scanning stage. Among them are cloning and healing tools, which can be used on local areas in the image, and global tools, such as dust and scratch filters and colour and brightness adjustment tools. Levels and Curves adjustments can also be handy for tweaking tonal values.

Levels and Curves adjustments allow you to correct tonal values in scans.

However, while the global tools may appear to be quick and easy solutions, they can compromise image detail and colour quality. There’s no advantage in changing areas that don’t need to be adjusted and some adjustments are better carried out in an image editor.

Be careful with contrast and sharpness adjustments. Both need to be applied with a light touch as excessive contrast can produce loss of detail, while over-sharpening can introduce noticeable artefacts and make images appear grainy.

Final Remarks

It’s easy to keep the scanner platen clean by wiping it periodically with a microfibre cloth or a slightly dampened lint-free cloth with a touch of mild soap. Spray-on cleaning fluids can leave streaks.

Allow plenty of time. Scanning is time-consuming and relatively tedious. If you’re good at multi-tasking, you may be able to do other things while scans are in progress. But keep them simple so you don’t lose track of what you’re doing and don’t divert processing power to activities that will slow down scanning.

Settle on an organisational system that’s easy to remember for the scans you make. Allocate folders for different occasions and subjects and tag scans with names you’ll recognise using names and, if possible, dates.