Image Thresholding 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.

Note: this JAVA applet has some layout problems under Mozilla and Internet Explorer; however, the applet should still work correctly and the layout errors should be obvious (separated histogram and axis labels, shrunk text input boxes).

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

Next to the input image is the histogram which has been generated from the input image. On the histogram image are two lines, one red and one green. The green line corresponds to the current lower threshold value and the red line corresponds to the current upper threshold value.

There are two slide bars which are used to change the values of the low and high thresholds. Sliding these along by depressing the mouse while the cursor is over them will change the position of the red and green lines in the histogram window, thus allowing you to see what areas of the histogram are being selected. The box above the slider records the threshold value. You can also enter data values into the box and pushing Return.

There is one pull down menu. This allows you to choose whether or not the output of the thresholding is inverted or not.

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.