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When captured images are saved, decisions must be made about the most appropriate file format. Numerous formats are available, and each has its advantages and disadvantages. The most widely-used file formats are:

  • RAW - As its name suggest, this format stores all the raw data from each pixel of a digital camera's sensor. Pixels are typically represented by 12-bit or 14-bit values which are reduced to 8 bits when stores in JPEG format. Images stored in RAW format therefore preserve all the available data but conversion software is required before image-manipulation can be undertaken. Colour settings and sharpening may be applied during conversion.
  • DNG - This is Adobe's Digital NeGative file format, an archival format for RAW files generated by digital cameras. This is an open-standard file format supported by a variety of software and therefore offers greater long-term archival security. The format offers a more efficient work-flow when handling RAW files from several different camera manufacturers. DNG is based upon TIFF/EP format and supports metadata. Conversion to the format may also save storage space.
  • TIFF- The Tagged Image File Format is probably the most widely supported high-quality image format. It caters for RGB and CMYK data and supports both lossless (ZIP) and lossy (JPEG) compression. Image dimensions and colour look-up tables are stored in a tag and added to the file header. Photoshop uses a variant that supports layers and clipping paths. File sizes are large. This file format is almost universally accepted by publishers and agencies of all descriptions.
  • PSD - This is the native Photoshop file format. It supports high-quality 48-bit colour images, layers, clipping paths and other image-manipulation features, but produces very large files.
  • JPEG - Developed by the Joint Photographic Expert Group, this file format uses multi-level lossy compression to reduce file format in dramatic manner. The associated algorithm examines an image and decides what detail is redundant. At high-quality settings only subtle tonal detail may be lost but as compression increases unwanted fringes, speckles and artifacts may become apparent. Compression to only 10% of the original file size may be possible.
  • HD Photo - This is a relatively new file format developed by Microsoft which aims to challenge the dominance of the long-established JPEG. It uses a lossy compression algorithm to reduce file size and allows users to specify quality and compression levels in much the same way as the JPEG. However, the resulting files are said to be only about half the size of those saved in JPEG format using the same image. The new file format may ultimately become known as the JPEG XR.
  • GIF - The Graphics Interchange Format uses a 256-colour indexed system designed for minimum file size. Its primary usage is in web-based applications. It supports simple animation by storing multiple images in a single file. Interactive buttons used on websites are an example of this. Clipart is also commonly saved in this format.
  • PDF - Portable Document Format preserves document text and typography, graphics, images and layout. The format is native to Adobe Acrobat, may be read but not edited by Acrobat Reader, and is used extensively by publishers for page design and layout.PNG - The Portable Network Graphic format features lossless compression. It has a number of applications in web-based applications. It is regarded by some as preferable to the JPEG format but has not been so widely accepted.
  • PNG - The Portable Network Graphics format offers the best compression algorithm available. Unlike JPEG compression, there is no loss of image data.The format has many options and supports binary transparency equivalent to the GIF format. PNG also offers 256 levels of variable transparency (254 between all or none), sometimes known as alpha transparency, which is supported by most modern browsers Microsoft IE 7 and later).This file format does not allow for animation.
  • MNG - This format is comparable with PNG and also supports animation. However, it is not widely supported by imaging software or web browsers.
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