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.
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
ASCII file, and second, how the
information is organized.
Common Graphic & 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.
In
Web-based
publishing, three file formats have become the widely accepted standard. Presently
Internet browsers can only read JPG or GIF and PNG images, without
the user installing a separate viewer or
plug-in. 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
80KB file |
Mid range compression & quality
8KB file |
High Compression / Worst Quality
6KB file |
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 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.
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 Formats
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 (Adobe
Photoshop Products)
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.
