Papers in PDF format

1 Introduction
The increase in computing power during the last few years has enabled personal computers to
deal with graphics very efficiently. To date graphics cards are available for a few hundred dollars
that can display images with a resolution of over one million picture elements (pixels) and
16,8 million colors. This makes image processing or at least display available to the average
end user. Due to this during the last years more and more image-applications for personal
computers evolved. They range from online shopping catalogs to spatial information systems,
from art galleries like „the Louvre“ to medical research databases, e.g. the „visible human project“
or the „dermatology online atlas“. Images are invaluable sources of information: „An image
is worth a thousand words“. All issues related to images will be discussed in the first section.
However it is quite difficult not to get lost among thousands of images. Therefore, there must
be a structured way to access images. That is where databases may help. However, there are
many different database systems, paradigms, features, etc. What kind of database is needed?
Would not an easy text search be everything one would like to have? Think of information
retrieval functionality. What about image manipulation features? Wouldn’t it be great if the
database could provide all this? How could images be described so that not only you but also
others may use the database? What kind of description is most suitable?
Can the database be connected to the Web to be useful to others? What tools are available?
Are there „out of the box“ solutions provided by vendors? How can the local database be interconnected
with other databases to create a global information infrastructure related to your
research field? Are there advantages of a WWW front-end even when not providing public
access to the database?
Finally, we will report how we answered all these questions when setting up our Dermatology
Online Atlas (DOIA) and discuss problems we came across and solutions we have found in
each of the above mentioned categories.
2 Images
This section is divided into six major parts. In the beginning we will cover some basics, continue
with manipulation, compression techniques, aspects of color in digital images, discuss file
formats and finally have a short look at Plug-Ins for Web-browsers.
2.1 Basics
2.1.1 Image Types
When talking of images the following categories can be distinguished:
• Object description
• Pixel graphics
• Mixed types
An object description describes not the image as a whole but the objects contained. Well
known file types of this category are the Computer Graphics Metafile (CGM), Word Perfect
Graphics (WPG) or Windows Metafile (WMF). For computer aided design there are extensive
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