Beta Version 1.0 by Bill Cameron & D.M. Gorski with contributions from the devotees of alt.binaries.clip-art 1999 - - --For the full-featured HTML version of this FAQ with working links-- http://www.wherever.it.winds.up.com A PDF version can be downloaded at the same location
a.b.c-a File Format FAQ This section is designed to present a list of the most common file formats found on alt.binaries.clip-art & a brief description of each. It is not, by any means comprehensive or complete. See also Bill Camerons' excellent description of raster .vs vector formats & the special section on JPEG vs GIF elsewhere on this page. If you would like to investigate any of these formats further a simple web seach will garner more information.
ART- AOL Graphics format Also a raster format read by First Image & Art Import BMP - MS-Windows bitmap format (Bit Mapped- Paintbrush)
BMP is the native bitmap file format of the Microsoft Windows environment. It efficiently stores mapped or unmapped RGB graphics data with pixels 1-, 4-, 8-, or 24-bits in size. Data may be stored raw or compressed using a 4-bit or 8-bit RLE data compression algorithm. BMP is an excellent choice for a simple bitmap format which supports a wide range of RGB image data.
CGM - Computer Graphics Metafile CGM is a file formatdesigned by several standards organizations and formally ratified by ANSI. It is designed to be the standard vector graphics file format and is supported by a wide variety of software and hardware products.
EPS - Encapsulated Postscript Files (also EPFS) EPS is a native Adobe© Postscript format which allows for the importing of graphics into compatible word processing software.
GIF - Graphics Interchange Form GIF (usually pronounced "Jif") is a data stream-oriented file format used to define the transmission protocol of LZW-encoded bitmap data. GIF images may be up to eight bits (256 colors) in depth and are always compressed. Despite the fact that GIF supports only 8-bits worth of colors, GIF still remains a popular choice for storing lower resolution image data.
JPEG - Joint Photographic Experts Group JPEG (pronounced "jay-peg") is a standardized image compression mechanism. The Joint Photographic Experts Group is the original name of the committee that wrote the standard. JPEG is designed for compressing either full-color or gray-scale images of natural, real-world scenes. It works well on photographs, naturalistic artwork, and similar material; not so well on lettering, simple cartoons, or line drawings. JPEG handles only still images, but there is a related standard called MPEG for motion pictures.
PCX - Used by PC Paintbrush (also called ZSoft paintbrush) PCX is one of the oldest bitmapped formats popularized by MS-DOS paint programs that first appeared in the early 1980's. PCX files may store mapped and unmapped image data from 1- to 24-bits in pixel depth, always contain RLE-compressed image data, and are recognized by almost all still-image graphics programs ever written
PNG - Portable Network Graphics Specification PNG (pronounced "ping") is a new bitmap. Its creation is an attempt to give the graphics community an alternative to the shortcomings and misgivings found in most popular file formats. The PNG format is intended to provide a portable, legally unencumbered, simple, lossless, streaming-capable, well-compressed, well-specified standard for bitmapped image files which gives new features to the end user at minimal cost to the developer.
TGA - Targa File Format The TGA format is one of the most widely used bitmap file formats for storage of 24- and 32-bit truecolor images. TGA supports colomaps, alpha channel, gamma value, postage stamp image, textual information, and developer-definable data.
TIF- Tagged Image Format The TIF (also TIFF) format was formerly owned and maintained by the Aldus Developer's Association. Aldus has since merged with Adobe Systems and now the Adobe Developers Association (ADA) maintains the TIFF file format.
WMF- Windows Metafile Format WMF is the native vector file format for the Microsoft Windows operating environment. WMF files are actually a collection of GDI (Graphics Device Interface) function calls also native to the Windows environment. When a WMF file is "played back" (typically usinindows PlayMetaFile() function) the graphics is rendered. WMF files e device-independant and have no limit to their size
GIF .vs JPEG Which one is "better?" The short answer is "neither" and "both" ;-) GIF format is better for images that have a limited amount of colors or large areas of a single primary color. JPEG is better for photographs or images that contain a large number of sublte shadings. If you'd like to know why... read on You've almost certainly used compression before, probably with a product like WinZip, StuffIt, or WinRar to pack down a graphic/text file to fit on a floppy before sending it off to someone or storing it for future use. The two main Internet graphics formats, GIF and JPEG, have such compression algorithims built in, but there are major differences between the two, as we shall see.
GIF
GIF, which stands for Graphics Interchange Format, is a "lossless" method of compression. All that means is that when the program that creates a GIF squashes the original image down it takes care not to lose any bits of information, so it available when the images is uncompressed by an image viewer. It uses a simple substitution method of compression. If the algorithm comes across several parts of the image that are the same, say a sequence of digits like this, 1 2 3 4 5, 1 2 4 5, 1 2 3 4 5, it makes the number 1 stand for the sequence 1 2 3 4 5 so that you could render the same sequence 1 1 1, obviously saving a lot of space. It stores the key to this (1 = 1 2 3 4 5) in a hash table, which is attached to the image so that the decoding program can unscramble it. The maximum compression available with a GIF depends on the amount of repetition there is in an image. A flat color will compress well - sometimes even down to one tenth of the original file size - while a complex, non-repetitive image will fare worse, perhaps only saving 20% or so. There are, however, some problems with GIFs. One is that they are limited to a palette of 256 colors or less. Compuserve, which created the GIF, did at one point say it would attempt to produce a 24-bit version of the GIF, but then along came problem number two: Unisys. Unisys discovered that it owned some patents to key parts of the GIF compression technology, (namely the LZW compression algorithim which is the key to the whole process), and has started demanding fees from every company whose software uses the (freely available) GIF code.
     JPEG
JPEG, solves the problem of the 256 color palette, in fact you can use uo to 16,700,000 colors in a single image. The catch is that JPEG is a "lossy" format. In other words in order to save space it just throws away parts of an image. Obviously you can't just go around discarding any old piece of information so what the JPEG algorithm does is first divide the image into squares (you can see these squares on badly-compressed JPEGs). Then it uses a piece of mathematics called Discrete Cosine Transformation to turn the square of data into a set of curves, some small, some big, that go together to make up the image. This is where the lossy bit comes in: depending on how much you want to compress the image the algorithm throws away the less significant part of the data (the smaller curves) which adds less to the overall "shape" of the image. This means that, unlike GIF, you get a say in how much you want to compress an image. However the lossy compression method can generate "artifacts" - unwanted effects such as false colour and blockiness - if not used carefully.
Portions of this FAQ Copyright 1994-96 by James D. Murray. Additions & Editing by Bill Cameron & David Gorski for alt.binaries.clip-art 1999. This work may be reproduced, in whole or in part, using any medium, including, but not limited to, electronic transmission, CD-ROM, or published in print, under the condition that this copyright notice remains intact.

    

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