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)
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
The input image is displayed in the Input display area
below the control buttons, along with the image size.
Note: you should only use square images (i.e. NxN) otherwise this implementation may give erroneous results.
The Fourier transform can be applied by clicking on the
"Fourier Transform" button. This must always be done first.
The result of the Fourier transform is displayed at the
upper right of the panel. There are several outputs that
can be displayed, and several ways to display them:
magnitude of the complex number output
logarithm of the magnitude of the complex number output
phase angle of the complex number output
real component of the complex number output
logarithm of the real component of the complex number output
imaginary component of the complex number output
logarithm of the imaginary component of the complex number output
Clicking on the label selects the given image.
The Magnitude Log image is often most helpful for understanding the Fourier output
Various filtering operations can then
be applied to the output of the Fourier transform:
Frequency domain area filter: the four numbers define a box
with diagonal from (X1,Y1) to (X2,Y2). Clicking
"Remove Area" or "Keep Area" modifies the Fourier
Apply Notch Filter: this removes pure vertical and horizontal high
spatial frequency components. The Width parameter controls the
notch width and the Radius parameter controls where the
Apply Frequency Filter: This applies a high or low pass stop filter
defined radially about the origin. The Radius parameter box
defines the cutoff frequency of the filter. The pull down panel
selects a High Pass or Low Pass Filter of the given radius.
Gaussian Smooth: the Fourier domain gets a low-pass
smoothing filter of the given theta. The Kernel Size controls
how large of a mask size is used, and Theta controls the
standard deviation of the Gaussian smoothing function.
When a filter is applied, you can see the results in the Fourier
domain output at the right.
Applying a filter might take a few seconds.
Clicking the "Reset Images" button removes the effects of the filters
and allows you to investigate new filters.
inverse Fourier transform can then be applied to view the effects
of the filtering in the spatial domain. The user must click on the
"Inverse Fourier Transform" button to do this.
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.
You can find out about known problems with the system