Hough Transform Experimentation

HIPR Applet Running Instructions

The following are instructions on how to run the applets which are part of the HIPR package. These applets are designed to allow the user to try out the operators which are outlined in the worksheets.

You may want to review the general instructions first, which gives a demonstration overview, JAVA details, browser details, known bugs, etc.

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 textfield labeled threshold is used to enter a threshold (a percentage of the maximum peak value, expressed as a number between 0 and 1) which determines which lines are accepted as real image lines.

The "Overlay" pull down menu allows you to select whether or not the input image should be overlaid on the detected line image. This is sometimes useful as a check that the lines that have been found do in fact exist in the image.

Pressing the green Apply Hough button starts the operator.

The outputs are displayed in the output windows which are positioned right of the input window. The first output is a picture of the hough space which the line voting was made in. The x axis corresponds to line angle, and the y axis is the radius from the center. The brighter the image is, the more votes were received at that point. The second output image is the picture of the lines which passed the threshold. These lines have been drawn in blue so that when they are overlaid on the original image they are easy to distinguish.

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.

Hough transform output may produce 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.

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.