Preparing photographs for publishing

Colour and resolution

For print

The process of printing reproduces images using microscopic dots of ink. In 4-colour or ‘CMYK’ (cyan, magenta, yellow and black) printing, dots are printed in each of the 4 colours at different densities and in rows at different angles so that the colours effectively combine in our vision to form continuous colour. The finer the resolution – that is, the greater the number of dots per inch (dpi) – the better and more accurate or lifelike the printed image will look.

Printed inks can create tens of thousands of shades – close to the human range of visual perception – but the results depend heavily on the paper or other surface on which the image is printed.

Photographs for printed publications need to be supplied as high-resolution electronic files so that they can be placed on the page at 300 dpi. Images for large-format printing (e.g. banners, large posters) can sometimes get away with 150–200 dpi if the quality of the image is particularly good, but it is still best to supply high-resolution images wherever possible. This will give the greatest flexibility in deciding how to crop and place images on the page. Images for CMYK printing should be supplied and placed as CMYK format.

File size is not necessarily a clear indicator of image quality, which also depends on the file format and level of compression (as well as the quality of the composition, lighting and focus, etc). As a rough guide, a high-quality JPG file size should be at least 2 MB for even a ¼ A4 page–sized image.

The photographs below show examples of different quality images. The photograph on the left is highly compressed (too low in resolution), resulting in pixelation, while the one on the right is not. Note that the focal range is very short, allowing the subject to be crisply in focus while the foreground and background are out of focus and thus less distracting.

To find out the resolution of your image, open the file with an image editing program such as Microsoft Photos, an image management program such as Adobe Bridge, or image processing software such as Adobe Photoshop. The image type, resolution and size are usually found via the file or image properties menu item.

Do not increase the resolution of the image by resampling it – resampling adds extra pixels by interpreting the adjacent pixels. It does not create or restore image data and will result in a fuzzy image.

For screen

A screen is packed with a certain number of pixels per inch (ppi) – for most computer screens, this is 72 ppi – in a fine mesh, each of which shows either red, green or blue (RGB) light at varying intensity.

Onscreen colours are limited by the combinations of red, green and blue pixels. It is almost impossible to accurately match an onscreen colour with a printed colour because of the difference in vibrancy and colour mixing methods.

Images for screen- and web-only use can be supplied or placed in a document with RGB values in a range of file formats. The minimum resolution of image files for onscreen viewing is 72 dpi.

Photographic file formats

Common image file formats include TIF, JPG, PNG and GIF. These open file formats can be edited by most image editing software applications and used in most page layout software applications. Most high-end digital cameras can produce both an open and a proprietary file format. Proprietary file formats, often referred to as ‘raw’ images or digital negatives, encode the data in such a way that only particular applications can open or edit the file. Proprietary formats typically do not compress the image data, so file sizes are usually very large. Your designer should be able to convert proprietary file formats to open file formats in a professional image editing program.

For books that feature full-page photography, TIF files are the most versatile. Use PNG or TIF files if the image contains transparency. Use GIF files for animations or small images such as logos. For most purposes, high-resolution JPG files should be suitable, but be aware that JPG is a compressed format – every time a JPG file is saved, the data are further compressed, which leads to deterioration of image quality. If editing a JPG image, save the edited version as a new file so that the original remains at the highest possible quality.

If you have only prints of your images, either scan them at high resolution or supply the prints to your designer, who should be able to scan them for you. Ensure that the surface of the print is clean before scanning – fingerprints or dirty marks can be almost impossible to remove from a digital image. For larger image plates, negatives, slides or other hard-copy image formats, you may need to seek a specialised service to digitise them.

Image adjustments

A publication designer should be able to make a range of adjustments to your images to ensure the best presentation. This can be done using specialised image editing software such as Adobe Photoshop.

Image adjustments can include brightening or darkening; reducing or increasing contrast; correcting exposure or white light balance; adjusting shadows and highlights; shifting colour balance, hue or saturation; changing colour mode between RGB, CMYK or greyscale; rotating, zooming, flipping or cropping; editing; extending or removing backgrounds; and deleting unwanted detail.

However, a designer cannot work with poor-quality images; the photograph must be of decent quality, high resolution and clearly focused to start with.