There are many advantages to shooting Raw images, from making edits that are impossible with JPEG images, to the ability to easily alter white balance. The term Raw simply refers to the fact that the data in a Raw image file has not been processed by the camera. To turn that into a usable image, you must still put the file through all the processes your camera employs when you shoot in JPEG mode (calculating colour, determining white balance, sharpening), but these steps are performed through raw converter software, such as Lightroom, Aperture, iPhoto, or Photoshop Camera Raw.

The advantages of shooting Raw image files usually outweigh the downsides (such as large file sizes) of working with the file type. Even if you don’t always shoot Raw, you should consider switching your camera to raw mode in the following situations:

White balance
Any time you’re shooting in a tough white-balance situation, such as when there is shade, cloud cover or mixed lighting, make sure you’re shooting Raw. With a Raw file, you can change the white balance of an image after the fact. If you’ve ever tried to correct a bad colour cast on a JPEG image with an image editor, you know how hard it can be to correct a white-balance problem. With Raw, this is never a concern. And while the auto white-balance mechanisms on most cameras are very good these days, they can still be tripped up.

Check out the clouds on the right to see where detail has been restored to the overexposed highlights. This edit would be impossible with a non-raw image

Overexposed highlights
You should always shoot Raw if you’re taking photos in a situation where it is difficult to control highlight exposure. In a Raw file, you can often restore detail to highlights that have been overexposed to complete white, and salvage otherwise unusable shots. This will be useful if you’re shooting in bright sunlight on a partly cloudy day, or in any situation with a lot of dynamic range; or if you’re shooting shiny objects that cast bright highlights.

Extensive editing and enlarging
If there’s no way to capture the scene the way you want, or if your image needs a lot of editing and adjustment, then switch to Raw. These files allow for much more editing than JPEGs. When you shoot in JPEG mode, your camera throws out data that it captures. Most of the time, this data loss doesn’t matter, but if you edit a lot, or plan on adjusting the contrast and colour to extreme degrees, the lack of data could leave visible artifacts in your image when you edit.

The JPEG compression algorithm is lossy – that is, when an image is JPEG-compressed, data is discarded, and the image is permanently degraded. Apply enough JPEG compression and the degradation will become visible. If you want to enlarge your image a lot, JPEG artifacts could be a problem. Because Raw files are not compressed, you never have to worry about this.

Avoiding the raw option
Raw is not a magic wand that will instantly create amazing images. In addition, Raw files are much larger than JPEGs, and it can take longer for the camera to write one out, which means that you may not be able to shoot bursts as quickly. On some cameras, a slow write time can mean you can’t shoot images as often.

With programs such as iPhoto, Aperture, Lightroom, and Photoshop (Elements and CS), Raw workflow is simple, and there’s little difference in post-production whether you shoot Raw or JPEG, so it’s worth a try.