Images and Image Formats

The HIPR Image Library

One of the major reasons for using HIPR is the fact that every image processing operation described in the package is extensively illustrated using good quality on-line digitized images. Viewing these images on a computer screen gives a much more realistic impression of what real image processing is like than is provided by looking at typical pictures in image processing textbooks.

In addition, every single image is stored in the HIPR Image Library, from where they can be used as input to real image processing packages. This extends the teaching potential of HIPR in a number of ways:

Students can compare the output of their own image processing package's operators with the example output images included with HIPR to see how different implementations differ slightly in functionality.
They can also experiment with the effect of changing parameters to operators to see how this changes the output. Suggestions of interesting things to try are given in the student exercises section of many of the worksheets.
Image processing operators can be tried out on additional images which are not used as test examples for that operator in HIPR.

And we are sure that users of image processing will find many other uses for such a large and varied collection of images. For example, as test images to new image processing algorithms.

Viewing Images with HIPR

As explained in earlier introductory sections, references to images in HIPR are made using imagelinks. To summarize briefly, these appear as small inline images known as thumbnails. Clicking on a thumbnail causes a full sized version of that image to be displayed.

This is an example of an imagelink:

Viewing images with the hypermedia version of HIPR is easy --- just click on the relevant imagelink. If you wish to view the images outside of this environment then things are slightly more tricky. You must use a piece of software called an image viewer and point it at the actual image file containing the image you wish to view. The details of how to do this vary considerably depending upon the machine architecture on which you are using HIPR, and so we cannot tell you exactly how to go about this. Typically though, you would proceed in one of two ways:

For the purposes of these examples assume that the image viewer is called `viewimage' and the image is called `test.gif'.

If you are using a command-line based system (i.e. one where you type commands at the computer and hit ENTER to get them executed) such as MS-DOS or a UNIX shell, then you would type something like:
viewimage test.gif

and press ENTER to display the image.
If you are using a windows system that doesn't provide a command-line prompt, then you would probably double-click on an icon representing the viewimage program, and you would then use that program's file browser to select the test.gif image to be displayed. Alternatively (e.g. on Macintoshes) you might just double-click on the icon representing the image file itself and the windows system would automatically start up an appropriate viewer to display that image.

Your system supervisor or course administrator should be able to advise you on the best way to do this. You may find more information in the Local Information section of HIPR.

The above discussion assumes that you know where the image file to be displayed actually is and what it is called. The location of images is discussed in the next section.

Two Types of Images

The images in HIPR can be divided into two different categories: raw images and processed images.

Raw images are simply images that have been digitized for storage on a computer, but as yet have had no (or very little) image processing done to them. Raw images are what are produced by devices such as video cameras and scanners.

Processed images are simply raw images that have had at least one stage of image processing applied to them.

This terminology is of relevance to image file naming conventions and to the Image Library Catalogue.

Image Directories and Formats

Note that if you are using a Macintosh computer, then a `directory' is the same thing as a `folder'.

All the example images used in HIPR are stored in the same directory: the images directory. This directory is just one of several which make up the HIPR system, all of which branch off from the HIPR root directory. This directory structure is explained in more detail in the section on Directory Structure.

To get to the images directory from the html directory (which is where the HTML files for the hypermedia version of HIPR are stored), first go up one directory to the HIPR root directory. Within this directory will be a sub-directory called images. This is the directory where all the image files will be found.

Again, your system supervisor should be able to help. Alternatively you might find details in HIPR's Local Information section.

Within the image directory, the images are, by default, stored in GIF (Graphic Interchange Format) files. This is a very common and convenient image format that is understood by many image viewers and image processing packages. However, your system supervisor may have chosen to use a different format if, for instance, the particular image processing package you use does not accept GIF. Converting the image files to a different format is described in the Installation Guide.