Papers in PDF format

hardware and platform independence, effective and lossless compression. In addition new
features have been added: Support for true color images of up to 48 bpp, greyscale images
of up to 16 bpp, full alpha channel (general transparency masks), gamma indication, detection
of file corruption, faster initial presentation in progressive display mode. The format is
simple (!), portable, interchangeable, and extensible without loosing interchangeability. The
compression with PNG is clearly superior to that achieved with TIFF. We tested 100 of our
images and got a compression ratio of 2.23 with PNG but only 1.29 with TIFF. Although
PNG is much more suitable for Web usage than GIF, PNG is only supported by a few
browsers.
• WVL: Wavelet. This is just one of the many wavelet formats available (e.g. [12]). Wavelet
compression is slowly starting to appear in commercial programs, for example Corel Photopaint
(enclosed with Corel Draw 6). It is offering good compression especially using high
compression factors, because the distortions look much more natural compared to the
blocking of JPEG. However, the implementations available right now are not compatible.
Thus, if you are setting up a big image collection and do want to use wavelet compression
keep a lossless compressed image in an archive.
A good starting point to learn about file formats is the Fileformats FAQ [13].
2.6 Plug-Ins and viewers
In the beginning of the Web the user was limited to GIF as graphics file format, later JPEG
appeared for inline images. Additional formats were available using viewers only. Viewers
worked fine, especially considering that they were specialized for a specific application. JPEG
images, for example, look much better if decoded in a viewer instead of the browser. This is
due to the slower but more precise calculation.
With plug-ins [14] it is now easier to use the image formats optimal for the application. Plug-
Ins exist for wavelet compression, fractal compression, vector images, etc. The advantage over
viewers is the direct integration in the browser. Thus, depending on the user community,
wavelet or fractal compression may now be a better alternative to JPEG, GIF, or PNG. Further,
plug-ins often provide additional functions like zooming. However, it has been shown,
that only a few users are willing to download plug-ins for viewing images. This may be a
problem unless you have a closed group accessing your information.
3 Database
Perhaps we should start with a definition, what is an „image database“? A strict definition
would be:
An image database is a database that stores images and supports the datatype
image with a set of functions.
These functions should include conversion from and to different file formats, scaling, change of
color depth, tiling, regions of interest, content based retrieval (CBR), filtering, etc. However,
according to this definition, to date there are hardly any image database systems available on
the market. People tend to talk of an image database when the database is able to store binary
large objects (BLOBs), sometimes viewing capabilities are offered. Because hardly any database
provides appropriate functions for image management, it is quite common to store images
in the file system and use the database only for links and administrative data.
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