Graphics File Formats
Graphics file formats are not created equal. Knowing which one to use and how to use it is the key to presenting pleasing images efficiently.
Terms to Know:
1) Graphics: (n.) Refers to any computer device or program that makes a computer capable of displaying and manipulating pictures. The term also refers to the images themselves.
2) File Format: A format for encoding information in a file. Each different type of file has a different file format. The file format specifies first whether the file is a binary or ASCIIfile, and second, how the information is organized.
Common Graphics & Image File Formats
Some of the most used and common graphics formats used today ate TIFF, JPEG, and GIF. The Tagged Image File Format (TIFF) is widely used in business, offices, and commercial printing environments. Initially TIFF was designed to alleviate the problems associated with fixed file formats and to eliminate the need for proprietary image file formats.
All About JPEG
In Web-based publishing, three file formats have become the widely accepted standard. On Web pages it is most common to find JPEG, or Joint Photographic Experts Group files used for photographic quality images. JPEG (or JPG) uses a lossy compression structure that allows users to compress the data up to 1/10 of the original size. Such high compression results in a loss of image quality, but on Web pages the images are generally small and they need the compression to produce the smaller image file sizes for downloading.
Most graphics programs will also allow the user to select a compression factor as you save a JPEG file, so you can work with the image to achieve a good balance between file size and image quality. As the compression factor gets higher, more artifacts are introduced into the image, which are blurred to make them less noticeable.
The three images below represent the lowest, mid-range and highest compression in a photo quality JPEG image.
|Low compression / Best quality||Mid range compression & quality||High compression / Worst quality|
All About GIF
The Graphic Interchange Format, or GIF, was developed by CompuServe to show images online when 8-bit video was commonplace. GIF uses a palette of up to 256 colors, which is why it is not suited to photo quality images where 24-bit color is required. GIF is best suited to common Web graphics like buttons, logos, text boxes, borders, and small animated images where the image is designed by the graphic artists and does not need more than 256 colors. A small background image for a Web page may only contain a few colors, in which case saving the image as a GIF file will produce the optimal file size for this type of graphic, especially when the graphic uses separate solid colors rather than shading.
Another important feature of a GIF file is that you can choose to save the background of an image as transparent. If you create a simple set of icons or text boxes for a Web page, saving these as transparent GIF files would allow you to implement the graphics on a variety of Web pages, regardless of the background colors you've used on the page. Most graphics programs will allow you to select a color within the GIF file to make transparent, or start with a transparent background and build your graphic up from there.
The GIF Compression Algorithm
The compression algorithm used in the GIF format is owned by Unisys, and companies that use the algorithm are supposed to license the use from Unisys. Unisys announced in 1995 that it would require people to pay licensing fees in order to use GIF. This does not mean that anyone who creates or uses a GIF image has to pay for it. Authors writing programs that output GIF images are subject to licensing fees. To this end PNG was developed as a patent-free answer to the GIF format.
The PNG Graphics Standard
PNG, or Portable Network Graphics, is the third graphics standard supported by the Web (though not supported by all browsers). PNG was developed as a patent-free answer to the GIF format but is also an improvement on the GIF technique. An image in a lossless PNG file can be 5%-25% more compressed than a GIF file of the same image. PNG builds on the idea of transparency in GIF images and allows the control of the degree of transparency, known as opacity. PNG does not support animation like GIF does.
Alphabetical Listing of Popular Graphics File Format
Animation Shop (.psp): Paint Shop Pro animation file (Paint Shop Pro Products)
CALS Raster (.cal, .cals): CALS files are used mainly for document imaging and only store black-and-white, 1-bit image data.
CompuServe Graphics Interchange (.gif): Developed by CompuServe, GIF uses a palette of up to 256 colors and is a popular choice for Web site graphics.
Deluxe Paint (.lbm): Used by Electronic Arts' Deluxe Paint package. LBM files use an IFF Bitmap header and IFF color map. As Electronic Arts progressed towards being a game developer, Deluxe Paint was abandoned.
Encapsulated Post Script (.sps, .ai, .ps): EPS is supported by most illustration and page layout programs.
GEM Paint (.img): The GEM image format is the saved bitmap file used by GEM Paint and Ventura Publisher
Interchange File Format (.iff): IFFs are 8 to 24 bit indexed color graphics or 8 bit interleave audio and are used on the Classic Amiga platform. Audio IFF files usually use a .snd extension.
JPEG (.jpg, .jpe, .jpeg): Joint Photographer's Exchange graphic (JPEG) is a compressed raster image format file. JPEGs are popular for Web-based distribution and display of photographic quality images.
JPEG 2000 (.jp2, .jc2, .j2k, .jpc, .jpx): The JPEG-2000 image compression system has a rate-distortion advantage over the original JPEG. It allows extraction of different resolutions, pixel fidelities, regions of interest, components, and more, all from a single compressed bitstream. JPEG-2000 also has options for lossy and lossless compression.
Macintosh PICT (.pct): Apple Macintosh Metafile supported by most Mac programs.
MacPaint (.mac): MAC files are used in the Macintosh MacPaint application. The MAC format requires always an image width of 576 pixels and a height of 720 lines.
Microsoft Paint (.msp): Mono bitmap format used mainly for Black-and-white drawings and clip art.
PhotoShop (.psd): Photoshop file.
Portable Bitmap (.pbm): Files are created by Jef Poskanzer's PBMPlus Portable Bitmap Utilities. The portable bitmap format is a lowest common denominator monochrome file format.
Portable Greymap (.pgm): Files are created by Jef Poskanzer's PBMPlus Portable Bitmap Utilities. The portable graymap format is a lowest common denominator grayscale file format.
Portable Pixelmap (.ppm): by Jef Poskanzer's PBMPlus Portable Bitmap Utilities. The portable pixmap format is a lowest common denominator color image file format.
RAW Graphics File Format (.raw): A flexible basic file format for transferring files between applications and computer platforms. This format consists of a stream of bytes describing the color information in the file.
SG Image File (.rgb, .bw, .rgba, .sgi): SG is the file extension for the Image file associated with SnapGraphix.
Sun Raster (.ras): The Sun Raster format is the native bitmap format on the Sun UNIX platforms. It is a simple bitmap format with wide distribution as it is supported by Sun OS and many UNIX based applications.
Tagged Image File Format (.tif, .tiff): TIFF is mainly used for exchanging documents between different applications and different computer platforms. It supports the LZW method compression for image types.
Truevision Targa (.tga): Developed by Truevision Inc. TGA files is a file format that will support images suitable for display on Targa hardware but is supported by many applications on a wide range of platforms.
Windows Meta File (.wmf): Graphics file format used to exchange graphics information between Microsoft Windows applications.
Windows Run-Length Encoded (RLE): The RLE format is a variation of the Windows BMP format that offers asome image compression. In Windows it can be used to create compressed wallpaper files or to replace the opening Windows logo screen.
Windows or OS/2 Bitmap (.bmp): Windows Bitmap file with color options of Mono, 4-bit, 8-bit, 24-bit. Compression is RLE, Huffman 1D, or uncompressed. This format is supported by Intel machines running OS/2, Microsoft Windows, Windows NT, Windows 95, and MS-DOS.
Wireless Bitmap (.wbmp, .wbm): WBMP is WAP (Wireless Application Protocol) graphic format optimized for mobile computing devices.
Z Soft Paintbrush (.pcx): Bitmap graphics file format, originally developed by Z-Soft for use with PC-Paintbrush. This file format is now uised and generated by many applications and scanners.
Based in Nova Scotia, Vangie Beal is has been writing about technology for more than a decade. She is a frequent contributor to EcommerceGuide and managing editor at Webopedia. You can tweet her online @AuroraGG.
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