This is from Martin Evenings book - Adobe Photoshop Lightroom 4, classroom in a book
About file formats
Camera raw formats Camera raw file formats contain unprocessed data from a digital camera’s
sensor. Most camera manufacturers save image data in a proprietary camera format. Lightroom reads
the data from most cameras and processes it into a full-color photo. You can use the controls in the
Develop module to process and interpret the raw image data for your photo. For a list of supported
cameras and camera raw formats, see
Camera raw, DNG | Adobe Photoshop CS6.
Digital Negative format (DNG) The Digital Negative (DNG) file format is a publicly available archival
format for raw files generated by digital cameras. DNG addresses the lack of an open standard for
the raw files created by individual camera models, helping ensure that photographers will be able to
access their files in the future. You can convert proprietary raw files to DNG from within Lightroom. For
more information about the Digital Negative (DNG) file format, visit
Camera raw, DNG | Adobe Photoshop CS6.
TIFF format Tagged-Image File Format (TIFF, TIF) is used to exchange files between applications and
computer platforms. TIFF is a flexible bitmap image format supported by virtually all paint, image editing,
and page-layout applications. Also, virtually all desktop scanners can produce TIFF images.
Lightroom supports large documents saved in TIFF format (up to 65,000 pixels per side). However,
most other applications, including older versions of Photoshop (pre-Photoshop CS), do not support
documents with file sizes greater than 2 GB. The TIFF format provides greater compression and industry
compatibility than Photoshop format (PSD), and is the recommended format for exchanging files
between Lightroom and Photoshop. In Lightroom, you can export TIFF image files with a bit depth of
8 bits or 16 bits per channel.
JPEG format Joint Photographic Experts Group (JPEG) format is commonly used to display photographs
and other continuous-tone images in web photo galleries, slide shows, presentations, and
other online services. JPEG retains all color information in an RGB image but compresses file size by
selectively discarding data. A JPEG image is automatically decompressed when opened. In most cases,
the Best Quality setting produces a result indistinguishable from the original.
Photoshop format (PSD) Photoshop format (PSD) is the standard Photoshop file format. To import
and work with a multi-layered PSD file in Lightroom, the file must be saved in Photoshop with
the Maximize PSD and PSB File Compatibility preference turned on. You’ll find the option in the
Photoshop file handling preferences. Lightroom saves PSD files with a bit depth or 8 bits or 16 bits per
channel.
CMYK files Lightroom imports CMYK files but adjustments and output are performed in the RGB
color space.
Video files Lightroom 3 will import video files from most digital cameras. You can tag, rate, filter and
include video files in collections, but editing is not supported. Click the camera icon on the thumbnail
of a video file to launch an external viewer such as QuickTime or Windows Media Player.
File format exceptions Lightroom does not support the following types of files: PNG files; Adobe
Illustrator® files; Nikon scanner NEF files; files with dimensions greater than 65,000 pixels per side or
larger than 512 megapixels.