Master your DSLR: image quality
EVERYTHING YOU NEED TO KNOW ABOUT JPEGS, RAW FILES AND IMAGE QUALITY SETTINGS.
WHEN IT COMES to setting the image quality on a digital camera, you’ll typically be given two options. The standard, straight-out-ofthe-box setting is JPEG. It’s a universally supported file format that doesn’t require specialist software to open, can be shared and displayed online, and be used to produce prints. JPEG is an acronym for the Joint Photographic Experts Group, the committee of experts that developed the JPEG coding standard. The other major file format offered by SLRs, CSCs and some high-end compacts is RAW. Actually, it’s really ‘raw’. It’s not an acronym, you see. In fact, raw files aren’t even really photos at all — not when you take them, at least. Raw files contain the raw information recorded by the camera’s sensor, along with details of the picture processing parameters that you dialled in on the camera — white balance, colour, sharpness, that kind of thing — when the raw file was recorded.
Because a raw file isn’t a picture, it needs to be converted to a standard format such as JPEG using dedicated raw-processing software, like Adobe’s Lightroom, before it can be shared or printed. Some cameras let you convert a raw file in-camera using a basic set of tools, which enables you to share an image or see how it looks with a different treatment. In fact, this is what happens when you take shots as JPEGs; each image starts life as a raw file, but your camera automatically converts it to a JPEG before saving it to the memory card.
So what are the main differences? Why would you choose JPEG over raw, or vice versa? Well, for a start, JPEGs enable you to shoot for longer. JPEG files are smaller in size — not in terms of resolution (a Large Fine JPEG has the same amount of pixels as a raw file), but rather in terms of the amount of space they take up on a memory card. The reason for this is that JPEG uses lossy compression, which means some image detail is lost in order to produce smaller file sizes. You can adjust the strength of the compression on the camera: the greater the compression, the more pictures you can squeeze onto a card, but at the expense of overall image quality.
Bear in mind, too, that your choice of camera settings are permanently applied to a JPEG before it’s saved to the memory card. While you can to some extent correct errors in exposure and colour later in photo-editing software, that involves reprocessing an image that’s already been processed once, when it was converted from a raw file to a JPEG and then compressed. When you process a raw file, you’re starting with the original source material, and that gives you a better starting point for any future edits.
The reason for all the file size and image quality adjustments is to enable you to make the most of your memory card space. But these days, memory is comparatively cheap. For the same $90 that it cost to buy a 1GB card a few years ago, you can pick up a 32GB or 64GB card, and still have enough change for a burger and a beer.
Of course, the resolution and file sizes produced by digital cameras has grown exponentially, necessitating the use of large-capacity memory cards, but you shouldn’t have to select smaller, lower-quality JPEGs because you’re running out of space.
Capacity isn’t the only consideration: memory card speed is just as important. Today’s SLRs are capable of capturing high-res images at higher continuous shooting speeds, so you don’t want your memory card to slow you down.