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Compass Edge Detector Experimentation

Source for this operator.

Image Loading

You can experiment with different images using any of the images supplied in HIPR or by a URL. Some of those available in HIPR have the prefixes given here and .gif as the file extension: grayscale (cam1, che1, cln1, fru1, man8, str1, str2, str3, tol1, txt2, wal2, wom1, wom2, urb1, xra1) and range (bae1, fac1, phn2, ren1, ren2, ufo1, ufo2, ufo3) images.

Enter image specifiers (into the edit box at the top of the screen) either as a full HIPR image filename (eg. cam1.gif) or by a full URL. Only gif files can be loaded. Because of JAVA security, the URL should refer to a publically accessible place, such as your public_html directory.

Pushing the Load Image button or pushing "Return" on the keyboard causes the specified image to be loaded. The input image is displayed in the Input display area below the control buttons, along with the image size.

Operator Instructions

The first pull down menu allows you to decide which of the kernel sets to use to detect the edges with. All kernels are defined in the HIPR worksheet for this operator.

The second pull down menu allows you to define whether or not the label image should should be labeled with different colors, or different grayscale values.

The "Color Map" button will popup a window showing the assignments of colors to directions. This is the same regardless of which set of kernels is used.

The output is displayed in the two output windows which are positioned right of the input window. The first window shows the label image which has been generated, while the second window shows the edge image with image intensity signalling edge strength.

Image arithmetic may produce images with values less than 0 or greater than 255. These values are clipped to 0 and 255, but Scaling and Offset values can be entered to allow you to rescale the images yourself before the clipping takes place, according to Output = Scaling*Input + Offset.

Edge detector output may have small values. You can use the scale factor to enhance the visibility.

Pressing the green start button causes the operator to run. Pressing the Stop button causes the operator to stop running. This is useful if the system being run on is very slow and the operator is taking a long time to complete.

The time box shows the amount of time which the operator took to complete the process on the input image. This operator might take several seconds to execute.

Image value inspection

You can inspect the input and result image pixel values by depressing the left mouse button and moving the cursor over the desired pixel. The pixel coordinates and gray-level value are displayed underneath the image. Note that some images are larger than the displayed 256x256 display window. Larger images are subsampled in an appropriate manner.

Known Bugs

You can find out about known problems with the system here.


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

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