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format in which an image file is saved. The format is identified by
the three letter extension at the end of the file name. Every format
has its own characteristics, advantages and disadvantages. By defining
the file format it may be possible to determine the number of bits per
pixel and additional information.
are saved in the default format belonging to the application with which
they were created.
Adobe Photoshop Document
Formats for Print
PostScript file format is supported by most illustration and page layout
programs, and in most cases is the preferred format for these applications.
Note that this is also the only file format that supports transparent
whites in Bitmap mode. This format contains raw PostScript along with
a low resolution screen PICT preview.
A page description
language which includes text as well as vector graphics and bit-mapped
images. This format is text-only and contains no screen preview.
(Tagged-Image File Format)
Mainly for exchanging documents
between different applications and different computer platforms. The Tagged
Image File Format was primarily designed to become the standard format.
The TIFF format supports LZW
method compression for image types. (This is the same compression used
by the GIF format for indexed color.)
Document Format (Adobe Acrobat)
can be read on any computer that has Adobe Acrobat Reader installed.
PDF file can be created from PS files using Adobe Acrobat Distiller,
or can be exported from most image manipulation and and page layout
Formats for WEB
Created by CompuServe
to upload documents to the CompuServe Information Service and to pass documents
between other types of computers.
The idea behind
designing GIF files was to create the smallest possible image file
for uploading and downloading from electronic Bulletin Board Systems (BBS),
thus producing a highly compressed format that minimizes file transfer
time over phone lines. The compression is accomplished by using the LZW
method for indexed color tables.
(Joint Photographic Experts Group)
economizes on the way data is stored and also identifies and discards extra
data, that is, information beyond what the human eye can see. Because it
discards data, the JPEG algorithm is referred to as "lossy". This means
that once an image has been compressed and then decompressed, it will not
be identical to the original image. In most cases, the difference between
the original and compressed version of the image is indistinguishable.
In general, compressed JPEG images have compression ratios of between 5:1
and 15:1. A trade-off does exist between the image quality and the amount
of compression. You do not need to decompress images saved in the JPEG
format. They are automatically decompressed when they are opened.
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