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Tuesday, January 4, 2011

Hi-Tech Studio: File Format Decoder Ring

The alphabet soup of file extensions is confusing. In this brief article, we show you the differences and similarities of the most common formats.

PSD. The Photoshop Document (PSD) file format is the native file format for Photoshop and was originally created as the only option for saving the variety of different layers, layer masks and other features available within Photoshop. This file format is proprietary to Adobe and utilizes lossless compression to help reduce overall file size. Pixel dimensions are limited to 30,000 pixels on a side, and the file size is limited to 2 GB.

PSB. The Photoshop “Big” (PSB) file format was created to address some of the limitations of the Photoshop PSD file format. Specifically, a PSB file can be up to 300,000 pixels on a side, and the total file size can (at least in theory) be up to 4 exabytes (4 million terabytes). For all practical purposes, simply think of a PSB file as being exactly the same as a PSD file, but with larger image size potential. This is mostly important for large-scale panoramas and other composite images of particularly high resolution.

TIFF. The Tagged Image File Format (TIFF) was originally created to provide a standard file format for scanned images. It since has grown into a popular file format, supported by nearly all digital imaging software, and even offered as a capture file format for some digital cameras. The TIFF file format is quite flexible, with the ability to store multiple individual components, which, for example, enables the file format to store layers in Photoshop. Compression, both lossy and lossless, is also an option for TIFF files. Adobe owns the TIFF specification, but hasn’t created any changes in the file format since 1992.

Tim Grey has authored over a dozen books on digital photography and imaging for photographers, including his latest release, Real World Digital Photography (3rd Edition), co-authored with Katrin Eismann and Sean Duggan. He also publishes the Digital Darkroom Quarterly print newsletter and the Ask Tim Grey eNewsletter. Visit www.timgrey.com.

All About Files:

In addition to the variety of image file formats photographers may have to contend with, there’s an entire category of “files about files” that you may run across. Here are some of the more common among them:

XMP. An eXtensible Metadata Platform (XMP) file contains metadata information about a RAW capture and generally is referred to as a “sidecar” file because it has the same base filename as the RAW capture and sits beside that file. Photographers generally will experience an XMP file as containing RAW conversion information about the RAW capture.

Bridge Cache. When using Adobe Bridge to manage your digital photos, a variety of information is cached about those images. This includes primarily thumbnail and preview images for the photos being managed.

Catalog. Adobe Lightroom and Apple Aperture (among other applications) store information about the images contained within a catalog in a database, which actually is a collection of several files. These catalog files contain details about all changes that have been applied to images, including which collections the images are contained in, adjustments applied to the images, and keywords and other metadata added to the images.


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