Understanding Camera RAW

As stated earlier, Aperture is revolutionary in its handling of Camera RAW image files. The Tibet images that you're viewing in Aperture now, and the images we'll use throughout this book, are Camera RAW images. If you're new to Camera RAW, here's a brief explanation of the format and what makes it so special.

The image sensor in a digital camera is made up of millions of individual light-sensitive elements. When struck by light, these elements convert light energy to voltage values. Then, an analog-to-digital chip converts the voltage values into digital data. At this stage, the data is in "raw" form. Many cameras allow you to save the raw data in a proprietary Camera RAW image file, without processing the image in another file format. In essence, all cameras with an image sensor use a RAW workflow.

Note

In some ways, the relationship between a camera's image sensor and Aperture is much like the relationship between the human eye and the brain. The image sensor in a camera is similar to an eye's rods and cones. In the same way that Aperture processes the data from the camera's image sensor, our brain processes information from our eyes' rods and cones.

The RAW format allows up to 16 bits of color to be stored, or 65,536 colors per channel. The analog-to-digital converters in high-end digital cameras use a 10- to 14-bit color space and then store images in a 16-bit RAW format. If you choose to process the data in your camera in a format other than RAW, you may be reducing perfectly good color information.

The decision to save in a RAW format is an option on many cameras. The RAW format contains the unprocessed image data plus additional, specific information about when and how a frame was shot. (This information is called metadata, which we touched on briefly earlier.) If you decide to save your images as JPEG or TIFF files, the camera processes the data in a format that may reduce the image's bit depth and sharpness and may affect its color. Decisions you make for image settings, such as sharpness and color, become permanently etched into the saved JPEG or TIFF files. Saving to a RAW format allows you to make such image-processing decisions during the postproduction workflow instead. Some cameras have a RAW+ mode that enables you to save RAW data and a processed version concurrently, which you may prefer if you plan on printing directly from the camera to a personal printer. Using this mode does, however, take up additional storage, as you are storing two files for each image.

There is no one RAW standard. RAW files have different nuances from manufacturer to manufacturer. Even products from a given manufacturer may have different versions of RAW. Aperture supports most of the major RAW variants, including CR2, CRW, DNG, NEF, and OLY, and Apple will continue to expand support as new RAW versions appear.

Note

Mac OS X has some built-in basic support for RAW images. RAW images can be previewed directly in the Finder's column view and in the Info window. Apple's Preview application can also open RAW images. These mechanisms are solely for preview purposes, and they provide basic information about file size, format, and pixel count without your having to open the image in an imaging application.

Understanding Other Image Formats

In addition to RAW, Aperture works with a number of processed-image file formats, including JPEG, PSD, and TIFF.

JPEG (Joint Photographic Experts Group) JPEG is often the default setting for point-and-shoot digital cameras, and most of the photos displayed on webpages are in this format. (The file extension is .jpg.) JPEG allows for a significant reduction in the file size of photographic images, but it is a lossy compression format. That means it groups the image data on the basis of the human eye's inability to perceive certain values. The less-perceptible areas are averaged together, and information is lost. This is referred to as lossy compression. Because of this lossy compression, it's important to always keep a digital original of JPEG images in a lossless format.

PSD This is the proprietary format for Adobe Photoshop files. It supports layers as well as a number of other proprietary features within Photoshop. Many applications, including Aperture, can display files in this format.

TIFF (Tagged Image File Format) Originally created by Aldus for PostScript printing, this flexible file format is universally read by most image-processing and layout applications. Files in this format have the extension .tif. The TIFF specification is controlled by Adobe Systems.