Most digital cameras record JPG images because the JPG format provides a very high degree of fidelity for photographs in a very small amount of space. JPGs are high quality, small, can be viewed quickly and easily on any computer, and look great when printed. But JPGs, like all image formats, also have some limitations. RAW is another image format that addresses some of JPGs problems. But no format is perfect and RAW images have problems of their own.
I'm about to get all geeky technical but bear with me for about three sentences. JPGs have two major limitations: they only record 8 bits of data per channel (red, green and blue) and all of the camera processing is "baked into" the image at the time it is captured. The number of bits per channel translates directly into the number of tones that are available for each color. JPGs can show 256 distinct tones for each channel. Normally it's not a problem, but it can lead to posterization in some images. If you've ever taken a photo of a sky and seen banding where the transition from one shade of blue to the next was not smooth then you've experienced the 8 bit JPG problem.
So what's that about baking? When you capture an image your camera applies a bunch of adjustments to it from contrast and sharpening to saturation and white balance. It then changes all of those pixels in the image and saves the result as a JPG on your memory card. In doing that, you lose a little latitude in how far you can manipulate the image later in software. You can't undo the sharpening, for example, if the camera applied too much.
A third issue some people mention is lossy compression but I don't really consider that a problem. The lossy compression issue is simply this: when you save a JPG, it doesn't save exactly the same image you opened. To achieve the small file sizes, some of the pixels are changed to allow the image to be compressed and use less disk space. With images like photographs, it's barely noticeable unless you use a coarse quality setting (most cameras let you choose from several quality levels with the higher quality images using more space). If you open and save the same JPG four or five times to make edits you will begin to see image quality suffer. Solution? Don't do that. Make all of your edits from an original JPG at one time and save the result as a new file. Want to make more edits? Open the original and repeat. You'll never be more than one generation from the original and if you save with a high JPG quality setting you'll never see a difference.
What RAW brings to the table
RAW is an image format (lots of formats actually since every manufacturer's format is different) that has some advantages over JPG. RAW files record the raw data directly from the image sensor (hence the name) and store it alongside the camera settings. RAW files also record 12 or 16 bits of data per channel, a huge boost over JPG in terms of available tones. Practically this means that you can apply whatever processing you want to the RAW data in post production. Since the camera settings aren't actually "baked into" each pixel, you can easily readjust sharpness, contrast, saturation and a ton of other settings directly on the source data. RAW files give you a high degree of control over the final output and allow you to perform operations on the highest quality original source data rather than making additional adjustments on top of previous adjustments like you must do with JPG. The upshot is that RAW can lead to a boost in quality in your final output.
In a sense, it's a lot like working with a digital negative. But that's also one of the drawbacks of RAW files. They can't be viewed in their native format without special RAW processing software, the extra data is nice but causes the file sizes to balloon tremendously leaving you with fewer shots per memory card, and each RAW file must be processed and then exported to a JPG format for printing or sharing (each image must be "developed"). It can be a slow and tedious process.
Only bad photographers shoot in RAW. Some people think that only lazy, bad photographers shoot in RAW because it allows them to correct a lot of shooting mistakes after the fact. Some photographers may actually use RAW as a crutch. But the best photographers always try to get everything right when the shutter is pressed. Shooting in RAW is just another tool to help them get the best quality out of their final output.
All pros shoot in format X. The truth is that many professionals shoot in RAW, many shoot in JPG, and many shoot in both depending on circumstances.
Shooting in RAW will improve your photographs. Well, maybe. RAW isn't going to improve your eye for light or composition. It isn't going to help you do lighting setups or improve your timing. It will allow you to squeeze every last bit of quality out of every image. But as the saying goes: garbage in, garbage out.
RAW can fix any exposure problems. RAW gives you some latitude in adjusting the exposure after the fact. Because of the extra data, you can get some highlight and shadow detail that would have been lost in a JPG. But changing the brightness of pixels in a RAW image isn't going to magic additional detail from nothing. A properly exposed image will always look better than one that was improperly exposed and adjusted later.
RAW is better than JPG (or JPG is better than RAW). Each format has its own distinct advantages and disadvantages. There are no absolutes and a lot of it depends on how you like to make photographs. Choose the format that works best for you.
In the end, RAW is just an image format that works well for some people and not for others. It's a tool that can be used to wring the maximum quality from any image but at the price of additional storage and post processing time. The only way to find out if RAW is right for you is to give it a try.
Is the quality really better?
That's the million dollar question, isn't it? When all is said and done and I look at images on my computer screen or hang prints, which format produces the superior result? That is the subject of my next chapter on RAW vs. JPG. Next time, I'll directly compare scenes shot in RAW and JPG both on a computer screen and in print. A real world head-to-head comparison of the formats to find out if RAW really is worth all the fuss.