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Common Graphic File Formats for Images

3,020 bytes added, 03:25, 7 July 2014
/* BMP: Windows Bitmap */
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A bitmap graphic may be referred to as a raster graphic.  When viewed at 100%, each dot corresponds to an individual pixel on a display. A file with the .bmp extension is an uncompressed bitmap.  Other raster graphic types, known as compressed bitmaps, include  JPEG, GIF, and PNG.  A bitmap is not a vector graphic.  If a bitmap image is enlarged it will always look blocky because each dot will take up more than one pixel.This file format was originally called the "Joint Photographic Experts Group File Interchange Format", or short, JFIF.  A JPEG bitstream is a sequence of data chunks, each chunk starts with a marker value.  For compression JPG mostly utilizes Baseline DCT / Huffman, providing lossy compression.  The image is a continous tone photo with five or more bits per channel.   This file format was originally called the "Joint Photographic Experts Group File Interchange Format", or short, JFIF.  JPEG is a universal format meaning files can be opened and viewed in almost all image viewing applications.  JPEG has existed for a long time and is a widely adopted format.   Baseline JPEG compression is the most common and is nearly synonymous with the use of the term JPEG.  A JPEG bitstream is a sequence of data chunks, each chunk starts with a marker value.  For compression JPG mostly utilizes Baseline DCT / Huffman, providing lossy compression.  The image is a continuous tone photo with five or more bits per channel.  When decoded, the image appears from top to bottom like a windowshade rolling down. Compression is variable and governed by a number of parameters with typical settings providing from 10:1 to 20:1 reductions in file size. The JPEG image format is ideal for producing highly compressed, true color images for the web.  Web designers attempt to achieve small file sizes for the images used in web design to accommodate visitors with limited bandwidth (such as dialup and DSL users.) The small file size doesn't come without a price.  Image quality is lost when saving as a JPEG (.jpg) and the higher the compression level selected, the more image quality is lost.  Furthermore, each time the JPEG image is reopened and resaved, even more image quality is lost.  Because of this JPEG is not suited for images that will be frequently modified, since detail is lost each time the image is saved.  JPEG files cannot have transparent backgrounds.  The JPEG format is limited to 8-bits for color data, yielding 16.7 million colors.  Although the human eye is not capable of discerning depths beyond this limitation, some modern digital cameras use 10-bit and higher color capture. ''Note that although Baseline JPEG lossy compression is what is widely used there are other more obscure implementations including a lossless JPEG ([[JPEG lossless coding mode]]).  It should also be noted that when using baseline JPEG compression, setting the quality to 100% in software when saving an image still results in image quality loss.  It is not implied that such a setting would switch to a lossless coding mode.''<big>Use: GIF</big><BR>''recommended file extension'': *.gif<big>Use: PNG or GIF</big><BR>''recommended file extension'': *.png, *.gif'''Reason''': '''Reason''': Typically PNG provides better compression, however, there are some examples where GIF results in the same or slightly smaller file size on gray scale images.<big>Use: </big><BR>''recommended file extension'': *.<big>Use: TIFF</big><BR>''recommended file extension'': *.tif'''Reason''':   '''Reason''':  Remember that RGB is for a video monitor display while CMYK is for print with ink (see [[RGB versus CMYK]]).  The TIFF image format supports multiple layers as well as RGB and CMYK color spaces, and even allows an image to contain spot-color channels.=== Many Graphic File Formats ===Including proprietary types, there are hundreds of image file types. Some of the formats that are most often used for purposes including web pages, email, digital photography, and desktop publishing are discussed on this page.  KEY WORDS: BMP GIF JPG JPEG PNG TIF TIFF WMFKEY WORDS: BMP GIF JPG JPEG PNG TIF TIFF WMF PDF EPS PSD CSD
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