Contrast Stretching 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

There is one pull down menu. It allows you to choose which of the three functions outlined in the HIPR page is used to stretch the image. The two boxes below this allow you to specify upper and lower bounds on the contrast stretching. These are bounds which the intensity values of the stretched image will lie between. The next two boxes are used only when the percentile method is selected, and specify upper and lower percentage boundaries of the image intensity values. These values are floating point numbers between 0 and 1. The final box is used when the cutoff method is selected and is used to specify a percentage value (float between 0 and 1) of the maximum intensity which is used to calculate the cutoff point in the image histogram.

The output is displayed to the right of the input image.

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.