DFT: Filtering in the Frequency Domain II

Building the Cantata Workspace

1. Read image barcode.viff and display it. Use operators User defined and Display Image.
2. Take the forward Fourier transform, determine its log(mag+1) magnitude spectrum and display it using operators FFT, Magnitudes, and Display Image.
3. Move the mouse over the magnitude spectrum of the image to determine the coordinates of the "stars" (coherent noise). Using the operators Constant, Circle Image and Inset create a frequency mask. Note: the mask should have value "zero" in locations to cancel the "stars", and the rest of the pixel values should be set to 1. Why? Select and appropriate diameter for the "zero-out" pattern.
4. Multiply your mask with the magnitude spectrum of the image and display the result. Use operator Multiply.
5. Take the inverse Fourier transform, determine the magtnitude spectrum and display the result. Use operators FFT, Magnitudes, and Display Image.
6. Determine the absolute difference of the two images and display the result using operators Absolute Diff and Display Image.

Exercises

• Perform the same experiment with different diameters of the "zero-out" patterns.