File Format Fun: Making the Right Choice

02/11/2009

Do you know your JPEGs from your GIFs? Are you perplexed by PNGs? We can help guide you through the myriad of file formats that you could use to store your favourite memories.

But before we give you the lowdown on the file formats you’ve heard so much chit-chat about, it’s time to run through some technical mumbo-jumbo.

There are two forms of compression: lossy and lossless. Now to state the obvious: one of them, lossless, means that your data is preserved in all of its glory, which obviously takes up a bit more space but retains its quality. Lossy means that less important bits and bobs (well, bits and bytes) get discarded to save space. This means that you can store more data on a smaller memory stick or hard drive, but you lose some quality.

Now you know the basics, we bet that you’re thinking “if there are only two main types of compression, then why are there so many file formats for my photos?” The truth of it is, these file formats have subtleties that allow you to store your photos in different ways. Used wisely, they can store your photos at an optimal quality taking up the minimum amount of space. But if you don’t use the right format you could end up with grainy, pixelated snaps which don’t reflect the quality of your original images.

Let’s start at the source – your camera. Pretty much every digital camera will take snaps and save them to memory card as a JPEG. It’s not a coincidence that they all do this – JPEG is great for photos. It’s a lossy file format, so it tries to get rid of features in the image that we simply can’t see. But if it gets too eager, things start to look odd, as shown in the example below.

It’s often possible to change the quality setting on a camera to balance quality against file size. This is separate from resolution, which is the number of pixels that actually get captured. The two need to be balanced in tandem though – there’s no point having a max quality JPEG of a puny number of pixels!

High end compact cameras and SLRs offer users something that makes no compromises on quality but gobbles up memory (not a problem if you’re stocked up on high capacity cards). “Raw” formats are the digital equivalents of negatives. They’re a copy of the image exactly as the camera took it. This is great if you don’t want to lose a single detail, but to process them you’ll need image editing software that can process your raw image – and each camera does it differently, so the software needs to be kept up to date.

With photography covered, let’s turn our attention to publishing images on the Internet. Bandwidth and download speeds matter, so if you’re putting up JPEGs it’s a good idea to shrink them down to a lower resolution and reduce the quality too, but remember – don’t go too far – a quality of between 70 and 85 leads to a small-ish file without too much loss of quality.

But what of other formats? PNG, which stands for Portable Network Graphic, is increasingly common on the web. It’s lossless, so saving an image as a PNG will compress it without any loss of quality. This is great for things like screen shots, diagrams, and logos, but for photographs, the files will be a lot bigger than a good quality JPEG. Still, PNG guarantees all detail will be preserved.

Then there’s GIF, stalwart of the Internet almost since its inception. GIFs are small – really small. They can also store animations too. The drawback is they can only use 256 colours, so saving a colour-rich photo as a GIF will result in loss of colour detail, with tricks such as dithering to try to make up for it.

After that adventure into the world of file formats, what are our conclusions? For photos, JPEG is usually the best bet – just be careful with that quality setting! For icons and basic diagrams, GIF or PNG are better choices, but remember GIF only supports 256 colours. And for the digital darkroom, work with raw images if your camera can produce them and convert them to something else only at the very end!

“But what about format ‘x’, Remember Kingston?” we hear you shout. Yes, there are lots of other formats, many of which aren’t used that much any more, or have very specific purposes. We’ve covered the ones you’re likely to want to use, and of course we’ve focussed only on images here. If you want to know more about other types of files, pipe up in the comments section and we will listen!