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26.01.09

Shooting raw

Words by Will Cheung

Let's be honest. For most photographers in most situations the format to shoot is JPEG. It’ll give high image quality, it’s universally compatible with imaging software and processing machines, and it’ll take up less hard disk space than Raw.

But if you want the ultimate image quality, Raw is the format to use. A Raw file has all the data that was recorded by the camera’s image sensor unlike a JPEG where valuable information is discarded during the compression process.

To get all technical for a moment, an 8-bit JPEG file can give 16.7 million colours, while a 16-bit TIFF processed from a Raw file can deliver, in theory at least, 281 trillion colours. On the face of it, you may think that shooting Raw isn’t worth the hassle given your needs and apparently minor gains in image quality. You can see this for yourself by doing your own test.

Put two A3 prints of the same scene on the wall, one from a well-executed JPEG and the other from a Raw file and the odds are you won’t see any obvious differences – even if your nose is pressed right up to the print. Yet despite all the compelling evidence that shooting JPEGs is the sensible way to go, there’s a great deal to enjoy with Raw despite the negative points and it can all be summed up in one word: flexibility.

I shoot Raw as a matter of course even though 95 per cent of my images go no further than the computer or are archived direct to DVD, and I urge you to do the same. But, and it’s a big but, only go this way if you have the time, software and commitment to get the most from the format. If you don’t, set the camera up properly, get your technique spot on and revel in the convenience and high quality of JPEG shooting.

JPEG files are smaller than Raw so you can get more images on a card. Obviously, the same applies when you come to archive the original files.
JPEG is a universal format. You can take the memory card out of the camera, pop into a photo dealer that has a processing kiosk and walk out with high quality prints.
Shoot JPEGs and you can shoot quicker, which is important for action. In the latest DSLRs you can shoot JPEGs continuously until a card is full.
Raw files need processing which is time-consuming and you have to work a little harder to get a finished image. A Raw file holds all the detail that the imaging chip recorded. This means you can adjust exposure and white-balance non-destructively, ie. the original Raw remains untouched.

Think of the future. It’s possible that Raw converters will become available that will give even better results from your existing files. On the other hand, it might well be that future software won’t be backwards compatible. Most camera makers use their own proprietary Raw format that can changes from one model to the next.

This may mean that the image-editing software you have been happily using for ages will need the latest plug-in or even a complete upgrade should you change cameras. There is a Raw file standard called DNG (Digital Negative), championed by Adobe, but this has yet to be universally embraced. Pentax and Samsung’s latest DSLRs both offer it.

Shoot Raw and if you mess up exposure or white-balance, you can easily retrieve the situation later on the computer. In some software packages you can even lessen digital noise during Raw processing. Such control is possible because Raws need an intermediate stage, ie. conversion, before you can enjoy your images. Raw also gives you the option of working in 16-bit, while JPEGs are limited to 8-bit.

Excuse all the numbers, but in an 8-bit file there are 256 brightness levels and up to 16.7 million colours. In a 16-bit file you get 65,536 levels and 281 trillion colours. This means that there are 256 brightness levels within each of the 256 brightness levels of an 8-bit file. You don’t get a wider brightness range but what you do get are a great many more levels that come into their own when you start tweaking an image’s tonal range.

This selection of unsharpened images was taken on a 10.2-megapixel Samsung GX-10 fitted with an 18-55mm zoom lens. One image was made in Raw, the camera’s highest quality setting, and then subsequent exposures were made in JPEG mode. Like most other DSLRs, the GX-10 offers different resolutions and compression modes – here defined as Good, Better, Best. Obviously, Good is more compressed than Better and Better more than Best.

The greater the compression the more data that is dumped by the camera when the image is written to memory card. We took shots in Raw and at the three JPEG resolutions and the three compression levels and enlarged each file to give the same, somewhat considerable, image magnification. This isn’t strictly a fair comparison (shoot a low res JPEG and you wouldn’t expect to enlarge it massively), but we wanted to show how the image deteriorates as resolution falls andcompression levels increase. The loss of detail is readily apparent in the JPEGs, and you can see that the Raw file is easily the best.

Shooting Raw gives image files with considerable flexibility when it comes to exposure. It means that you can make a complete hash of the exposure and still be able to retrieve an acceptable image during Raw processing. To show what can be done, we took a shot at Birling Gap, on England’s south coast, using a Canon EOS 5D with a 17-40mm f/4 zoom lens. It was early morning and the low, bright sun gave a contrasty scene.

The meter said that 1/125sec at f/16 was the ‘correct’ exposure so this is what we used. The camera was set to give simultaneous Raw and JPEG. We took a series of pictures around our determined correct exposure using the camera’s compensation feature: at +1, +2, -1 and -2 settings. Back home, using Photoshop CS2, the JPEG files were opened. Using the base exposure file as our control and using the Levels command, we tried to get the same density and tonality on the under and overexposed JPEGs.

Next we processed the Raw files, also in Photoshop CS2. The correctly exposed file was processed with no changes to the exposure. On the under and overexposed files the Exposure Slider in the Camera Raw interface was adjusted to give a density similar to the correctly exposed file.

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