Chapter Six. Editing Raw Files

By default, your digital camera probably outputs JPEG files. JPEG (short for Joint Photographic Experts Group, the organization that created the JPEG specification) is a fairly amazing technology that makes it possible to greatly reduce the file size of an image with little discernable loss in quality.

JPEG files are ideal for digital cameras, where storage space can be limited and a smaller file size can mean a speedier camera. But JPEG files require your camera to do a lot of extra work. To create a JPEG file, your camera has to perform a substantial amount of image processing, some of which is the same type of processing that you do in your image editor.

When your camera creates a JPEG file, it makes some decisions about color processing, sharpening, noise reduction, saturation, and tone. While a good camera will make very good choices when applying these effects, they may not be the ideal choices for every image. More important, though, is the fact that if the camera has already manipulated your image data to achieve certain effects, you may have less latitude when you apply your own adjustments.

As you saw in the last chapter, it is possible to push an edit too far and end up with a final image that has tone breaks and other artifacts. With a JPEG image, your camera has already performed a fair amount of processing, which means that you'll encounter artifacts much sooner when editing.

What's more, while your camera may capture 10 to 12 bits of color data per pixel, JPEG files support only 8 bits of data. This means that your camera must throw away a lot of the color information that it captures when it converts to JPEG. You may not always see the effects of this lost data, but you'll probably feel them when you're editing. You'll have far less latitude for making adjustments.

Fortunately, these days many camerasfrom simple point-and-shoot to high-end SLR include the capability to shoot raw images. Aperture provides thorough raw support, and this chapter explores all of its raw capabilities. In addition to learning some new tools, you'll take a look at the raw-specific features of some of the editing adjustments that you've already used.