I always shoot raw. For me, the advantages of shooting raw image files have long outweighed any of the issues sometimes associated with working with the file type, like limited storage. But even if you're not interested in permanently switching your camera from JPEG into Raw mode, it's worth learning what raw is (and isn't), and when switching over to raw might mean the difference between usable and unusable results.
What is raw?
The name "raw" is not an acronym—it simply refers to the fact that the data in a raw file has not been processed by the camera. There are numerous raw file formats, and your particular format depends on the type of camera you are using.
When you shoot an image with your digital camera, a lot of things happen very quickly. Your image sensor is exposed to light, which results in the surface of the sensor having a unique electrical charge for each pixel on the sensor. These charges are read from the sensor and assigned a number (that is, they are digitized), which corresponds to how much light hit each pixel. However, this number doesn’t give any indication of the color of the pixels. If you are shooting in raw mode, these numbers are immediately written to the memory card as is.
If you are shooting in JPEG mode, there are a few more steps the image goes through in-camera. The data is transferred to the camera’s on-board computer, which performs a very complex process called demosaicing that determines the color of each pixel. The resulting color image is then adjusted in various ways, including being white balanced to compensate for the type of light you were shooting in. Then the image is sharpened, compressed so that it doesn’t take up as much space, and finally stored on your memory card.
Since a raw image is not converted into a color image, processed, or compressed, it is truly, raw data. To turn that raw data into a usable image, it still has to go through all those processes that your camera employs when you shoot in JPEG mode, but these steps are performed by your computer, using raw converter software, such as Lightroom, Aperture, iPhoto, Photoshop Camera Raw, and others.
When to shoot raw
There are many advantages to shooting raw, from making edits that are impossible with JPEG images, to the ability to easily alter white balance. In general, processing images on a computer instead of in-camera means you’re in charge, so you can tailor all raw conversion decisions to your taste and needs. And because your computer doesn’t have to rush to process the image (your camera, after all, needs to be ready to take another shot) it can use more sophisticated raw processing algorithms.
Even if you’re not convinced to always shoot raw, you should still consider switching your camera to raw mode in these specific situations:
When you’re unsure about white balance
Any time you’re shooting in a tough white balance situation, like when there is shade, cloud cover, or mixed lighting situations (sunlight streaming into a flourescently-lit room, for example), 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 colorcast 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.
Of course, you can manually white balance to solve this problem but shooting raw is easier, especially if you take a shot of something gray, which you can use as a reference later. With raw, you just won’t have to worry about white balance.
When you’re facing highlights that might overexpose
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 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, shooting shiny objects that cast bright highlights, shooting in any situation with a lot of dynamic range (range of dark to light), or shooting people shots on a hot day, when sweaty skin can tend to overexpose.
When you plan on doing extensive editing
Raw files allow for much more editing than JPEG files. Your camera probably captures 12 to 14 bits of data per pixel, but a JPEG file can only hold eight bits of data per pixel. This means that, when you shoot in JPEG mode, one of the first things your camera does is throw out a bunch of data that it captured. Most of the time, this data loss doesn’t matter—you still get an image that has the full range of tone and color that your camera can yield. But if you like to edit a lot, or if you plan on adjusting the contrast and color to extreme degrees, then this loss of data could mean trouble. A data-poor image won’t stand up to as much editing as a data-rich image, so you might start to notice banding patterns in darker gradients like chrome, if you perform too many edits on a JPEG image. Sometimes you might see banding in skies as you edit.
With that in mind, if there’s simply no way to capture the scene the way you want in camera, or if you think your image will need a lot of editing and adjustment, then switch to raw. This might be a scene with a lot of dynamic range, or a scene where color reproduction is critical, and you want the ability to perform precise adjustments.
When you’re going to enlarge an image
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.
When not to shoot raw
Keep in mind that raw is not a magic bullet that will immediately make your images look better. Raw files will not be sharper, or have more detail or more saturated colors than a JPEG. In fact, right out of the camera, they may be softer and lack the punch of a JPEG. In addition, raw files are much larger than JPEG files, which means your storage card won’t be able to hold as many images, and it can take longer for the camera to write out a raw file, which means you may not be able to shoot bursts as quickly. On some cameras, slow write time can even mean that you can’t shoot images as often. Also, if you ever like shooting at low pixel counts, say for web delivery, note that on most cameras raw files can only be shot at the maximum pixel count of your camera.
Try it out
In the early days of raw, workflow was a hassle. But with iPhoto, Aperture, Lightroom, Photoshop (Elements and CS), raw workflow is now simple, and there’s very little difference in post-production whether you shoot raw or JPEG, so there’s really no reason not to give it a try!
[Macworld senior contributor Ben Long is the author of Complete Digital Photography, fifth edition (Charles River Media, 2009).]