Editing RAW Files

Some digital cameras offer the option of shooting in RAW format, in which the image isn't compressed at all. RAW is considered a "digital negative" format that isn't to be modified, which has some implications when you want to edit a RAW photo in iPhoto.

Useful facts about working with RAW:

• The first time you edit a RAW file in iPhoto, a small RAW badge appears in the lower right corner of the display pane. On subsequent edits, the RAW badge doesn't appear.

• On that initial edit, iPhoto converts the RAW file to JPEG, leaving the RAW file in the Originals folder in your iPhoto Library folder and storing the JPEG version in the Modified folder. All changes are made to the JPEG version.

• JPEG is an inherently lossy compression format, which means that some detail is lost. iPhoto 6 now offers you the option to save edited RAW files in TIFF format, which uses lossless compression to preserve all the original detail in the RAW file. Change this setting in the Advanced pane of iPhoto's Preferences window by selecting Save Edited RAW files as 16 Bit TIFFs (Figure 4.7).

  Figure 4.7. Set your RAW preferences in the Advanced pane of the iPhoto Preferences window.

  

• If you prefer to edit RAW files in an external editor like Adobe Photoshop, you can select Use RAW Files with External Editor in the Advanced pane of iPhoto's Preferences window (Figure 4.7). That setting overrides iPhoto's normal preferences for how you edit photos.

• If you select an edited RAW photo (really the JPEG or TIFF version) and choose Revert to Original from the Photos menu, iPhoto reverts all the way back to the RAW file.

Lossy vs. Lossless Compression

There are two basic ways of compressing a file so it takes up less space on disk: lossy and lossless.

With lossy compression, some data is deleted from the file, usually in ways that aren't particularly noticeable but that always reduce the overall quality. Files compressed with lossy compression methods are usually much smaller than their originals. Lossy compression methods work well with pictures and sound where data that most people can't see or hear can be eliminated.

In contrast, lossless compression methods preserve all the data in the original file perfectly when compressing it. That's best for retaining quality, but means that the files aren't nearly as small.

The basic difference then, is the trade-off between size and quality. For higher quality, choose file formats like TIFF that use lossless methods of compression; for smaller files, stick with file formats like JPEG that use lossy compression.