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How to Use the Worksheets

The Role of the Worksheets

The worksheets which make up the middle section of HIPR are probably the most important part of the reference. They provide detailed information and advice covering most of the image processing operations found in most image processing packages. Generally, each worksheet describes one operator. However, in addition, many worksheets also describe similar operators or common variants of the main operator. And since different implementations of the same operator often work in slightly different ways, we attempt to describe this sort of variation as well.

The worksheets assume a basic knowledge of a few image processing concepts. However, most terms that are not explained in the worksheets are cross-referenced (via hyperlinks where applicable) to explanations in the A to Z or elsewhere. This means that the worksheets are not swamped with too much beginner level material, but that at the same time such material is easily available to anyone who needs it.

Some of the worksheets also assume some mathematical knowledge, particularly in the descriptions of how the various operators work. However this is rarely important for understanding why you might use the operator.

Worksheet Organization

The worksheets are divided into nine categories:

These categories are arranged in very approximate order of increasing difficulty (so that the easiest and often most useful categories come first). The categories are largely independent however, and may be tackled in any order.

Within each category, the individual worksheets are also arranged in approximate order of increasing difficulty and decreasing usefulness. The worksheet ordering is slightly more important than is the case with categories, since later worksheets tend to assume some understanding of earlier worksheets. However, as usual, any references to information contained in earlier worksheets will take the form of hyperlinks that can be quickly followed if necessary.

The Elements of a Worksheet

Each worksheet nominally consists of the same set of sections, although some of them are omitted on some worksheets. The sections are:

Common Names

The main heading of each worksheet gives what we believe is the most appropriate name for the operator concerned. This is usually the commonest name for the operator, but is sometimes chosen to fit in with other operator names. The purpose of the Common Names section is to list alternative names for the same or very similar operators.

Brief Description

This section provides a short one or two paragraph layperson's description of what the operator does.

How it Works

Unsurprisingly, this section explains how the operator concerned actually works. Typically, the section first describes the theory behind the operator, before moving onto details of how the operation is implemented.

Guidelines for Use

This is one of the more important parts of the worksheets, and often the largest. This section provides advice on how to use an operator, illustrated with examples of what the operator can do, and examples of what can go wrong. An attempt is made to provide guidelines for deciding when it is appropriate to use a particular operator, and for choosing appropriate parameter settings for its use.

The Guidelines section contains imagelinks like this one:


which represent example images.

Image links appear as small pictures (known as thumbnails) which when clicked on cause the corresponding full-sized image to be displayed. Try it.

The Guidelines section often provides worked through examples of common image processing tasks that illustrate the operator being described.

Common Variants

This section is optional, and describes related operators that are not sufficiently different from the current operator to merit a worksheet of their own, but have not been adequately covered in the rest of the current worksheet.


Exercises are provided to test understanding of the topics discussed on the worksheet. A proportion of the questions involve practical exercises for which the use of an image processing package is required. Suggestions for suitable test images from the image library are also given.


This section lists bibliographic references in a number of popular image processing textbooks for the operator concerned.

Local Information

This section is provided to allow the person in charge of installing HIPR to add information specific to the local installation. Suitable information would include details about which operators in local image processing packages correspond to the operator described. More details are given in the section on adding local information.

Navigation Buttons

At the top of almost every page in the hypermedia version of HIPR appear up to four navigation buttons. On pages that occupy more than about a screenful, the buttons are duplicated at the bottom of the page. These navigation buttons help the user navigate around the worksheets quickly, and have the following functions:

Go to the top-level page.

Go left one page, when in a linear series of topics. Note that this is not the same as the Back button described elsewhere.

Go right one page, when in a linear series of topics. Note that this is not the same as the Forward button described elsewhere.

Go up one level

To understand the operation of the navigation buttons, refer to Figure 1 which shows part of the structure of HIPR.

Figure 1 The structure of part of the worksheet section of HIPR. The arrows show possible transitions between HIPR pages, and the arrow type indicates how this transition is achieved.

As the figure shows, the structure of HIPR is somewhat like the root system of a plant (or a tree turned upside-down), with each node branching out into finer detailed nodes. With this picture in mind it should be fairly easy to see how the various navigation buttons work.

Note that the left and right arrow buttons are not equivalent to the Back and Forward buttons provided by Netscape (at the top left of the screen). The Back button simply reverses the effect of the last link followed (no matter whether it was via a navigation button or via a hyperlink in the text of a worksheet). The Forward button can only be used after the Back button has been used, in which case it undoes the backwards jump.

It is possible, by following too many hyperlinks in succession, to become `lost in hyperspace', i.e. to become confused as to where you are in the HIPR structure. In this case it is quite a good idea to press the Back button repeatedly until you return to somewhere you recognize. Alternatively, just hit the Home HIPR navigation button to get back to the top level again.


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©2003 R. Fisher, S. Perkins, A. Walker and E. Wolfart.

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