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. |
NEXT