A recent worldwide poll by Momentum Research Group found that 93% of designers used digital stock photography in the last 12 months. The same poll a couple of decades ago would have yielded very different results. Back then, the transparency was the only real method of image supply and digitisation was almost unheard of. So what has caused this dramatic rise in fortune for the digital image? Apart from the near universal use of digital design and production processes, and the fact that today's designers are undertaking more and more cross media campaigns that require keenly priced imagery, the most obvious factors are choice, speed of delivery and quality. And these three factors are the very reasons why it makes sense for users to choose digital imagery nowadays.

Choice of Images and Finding the Right One
The choice of images available has never been so good. Improvements in digital photography equipment have made it easier for photographers to make images instantly visible to a worldwide audience via their own websites or stock agency sites. Likewise, falling costs of digitisation mean that a lot of very interesting publicly owned and commercial archival material is becoming increasingly available in digital formats. Some picture libraries are also making it easier for photographers and smaller agencies with material that would not be accepted by large players, (because, for example, of the small size of the collection), to go digital and get online, making niche and speciality imagery more widely available.

Of course, when you are trying to locate the right image more choice isn't necessarily a good thing. You need to find the right agency and, if you are to find the image you want online quickly and efficiently, that agency needs to have a good search engine. Trade organisations such as BAPLA can point you in the right direction if you haven't already been inundated with catalogues. You will soon learn which agencies have the better search engines by the quality of results you receive and the speed at which they are presented. The good news is that most online picture libraries invest time and effort in developing customer-friendly and fast search facilities. However, even the best online search engines retrieve thousands of images, so unless you want to be bombarded, you'll need to narrow down the results using advanced options (which tend to cover everything from orientation to file size), boolean searches (using 'and', 'or', 'not', etc) or, if you are looking for something specific, placing the search terms in inverted commas to eliminate irrelevant results.

Once you've successfully located and downloaded the pictures you want, you should store any images that can be reused (these being royalty free images, unless you have negotiated a multiple usage for a rights protected photograph) in a content management system, available from providers such as Extensis, iView and Markware. They can also help you manage fonts and other media, and are particularly useful if there are a number of people in your organisation using the images.

Getting the Best Results from your Digital Images
The quality of digital images and the output achieved from them is affected by many factors, each of which can be controlled independently. The most important factor is the quality of the original material—the better the original, the better the end result. Many people still believe that transparencies are of a superior quality to digital images, but this is pure myth. Transparencies and slides have to be scanned in today's workflow scenario. This means the quality of the scan is, to a degree, device-dependent (although a bad original will give a bad scan however sophisticated the scanning device and software), added to which the scan will almost inevitably need some retouching to get rid of dust and scratches. Photos taken on a digital camera can be reviewed straight away, don't have to be retouched and the old issues, e.g. unrealistic looking flesh tones, have been resolved by increasingly sophisticated cameras, so quality really is not an issue.

It used to be argued that the compression of digital imagery impacted quality but techniques today are so advanced that this is not the case. JPEG files, the most common file format, are compressed versions of the original file and mean that you can download images quickly without compromising on quality. (A good tip on file sizes is to remember that the file size of a JPEG does not relate to how big it will appear in print. This is because some images compress better than others, depending on how much detail is in the image).

Is What You See What You Get?
Good, consistent colour, an issue for designers since the inception of digital publishing, is also a crucial mark of quality. No amount of colour management by a stock agency, or anyone else in the 'image chain', can improve a poor original photograph. That is why it is important for stock libraries to reject images that do not meet colour quality standards. Problems with an original photo are compounded when it is used across print, online, and wireless campaigns where factors such as screen and printer settings can impact colour. If you then recreate the materials in other countries where everything, including ink and the chemicals in paper, can vary, then dramatic inconsistencies can occur.

As long as you and everyone in the image chain, from the original photographer through to the printer you use, has calibrated their monitors and printers properly, you can expect the images that you choose online to look the same as the final output. A recent report by Trendwatch showed that very few printers and even fewer designers and publishers implement this form of colour management, which is frightening considering it is so simple to set up and can cause so many issues if it is ignored. Calibrating a monitor includes adjusting its settings to compensate for the conditions you are working in (i.e. some monitors are viewed in natural light, others under artificial light), and ensuring that your computer has the correct colour settings for the printer. If the monitor you use for finding images cannot be accurately calibrated (perhaps because your printing is handled by a third party), you should add a step to your final image selection process that includes viewing the images on a calibrated monitor. Excellent colour software packages, for example Gratagmacbeth software and Adobe Gamma, make the process easy nowadays, so there is really no excuse for bad quality colour.

While we are on the subject of colour, let's look at the differences between CMYK and RGB and how they relate to the quality of the final piece. RGB is the most common colour mode a digital file will be delivered in and as it is the basic model for screen display, it works well for designers. For printers, however, all work has to be in CMYK. This stands for cyan, magenta, yellow and key or black and relates to the four so-called process colours that are used in the four-colour printing method (often incorrectly referred to as 'full colour printing'). When the conversion takes place, colour shifts can occur (particularly in the intense reds, and greens). This is when you hear the cry "why doesn't what I printed match what I see on my monitor?" This is yet another reason why calibration is key at every stage and also illustrates that it's important to choose a printer and/or designer who realises its importance.

Size Really Does Matter
Quality issues can also occur if you choose the wrong size of image for the proposed use. Determining the resolution required is the key to getting this right. 'Resolution' can mean one of two things depending on the context in which the term is used. If you ask what resolution an image is, you will get an answer in pixel dimensions. Pixels are small squares of colour, like tiles, that make up the image in digital files. The pixel dimensions of an image (i.e. the number of pixels high and wide) are often supplied by stock agencies to help you estimate how much detail will be included in every cm/inch printed and therefore how large the image will comfortably print/appear on a screen before it becomes 'pixelated' (distorted). However, before you can work that out, you need to know how many 'dots' (a dot is roughly equivalent to a pixel) your printer can fit into an inch (known as 'DPI' or 'dots per inch'). If you need an image of a minimum size for a project, then you will need to provide the size the image will be reproduced at (in inches or cm) and the print resolution (in dpi) that will be used. Ask your printing department if you are in any doubt. If they say '300 dpi' (a common setting for magazines, brochures etc.), then you can work out the print size as follows; Image dimensions: 2056 x 3000 pixels; 2056/300 = 6.8 inches wide and 3000/300 = 10 inches high.

For most book, magazine and brochure printing, the print resolution typically needs to be 300dpi and above. Large format prints, such as billboards, are usually printed at lower resolutions of under 150dpi (the image is less detailed because it is viewed from farther away) although it's worth checking with your print department before you start. If they require a higher resolution, that is normally not a problem as agencies can often supply extra large files using a process called interpolation, which increases the resolution without impacting the quality. However, once you have received the image, whilst you can shrink it, it cannot be easily expanded without losing quality.

Final Considerations
We have already covered some of the 'deadly sins' that can lead to a poor end result from digital images. A final consideration, which can lead to an imperfect job if it is not checked, is ensuring that when you supply a final file, you check that your printer has everything he needs to work on the job. Common issues at this stage include missing images, images that are the not the correct resolution (these are mainly supplied in low resolution, although this also includes those that have been resized or modified in another way) or are in the wrong file format.

In 2002, according to a survey conducted by a leading design software company, more than 70% of files were supplied with errors that prevented them from being printed correctly in the UK alone. 62% of designers also spent 10 to 20 minutes communicating with customers resolving file errors. In terms of time wasted, this equates to a staggering 40,000 to 75,000 pounds in non-billable hours. This is where a pre-flighting system, rather than what is usually referred to as 'eyeballing' (checking manually) can help. Systems like these will give instant reports on any problems/omissions and some can even automatically correct the problems too.

So, as you can see, finding the right digital image and getting good results is not difficult as long as you know the basics. If you are still worried about taking the plunge, then it is worth calling a picture library and getting their help with anything from picture searches through to interpolation and colour management.

James West is CEO of Alamy Images.