Representation and Description
Theoretical Assignments
Question 1: Plot the signature of a square boundary using the tangent angle method
discussed in Section 11.1.3 of the text book.
Question 2: Find an expression for the signature of each of the following boundaries,
and plot the signatures
a) an equilateral triangle
b) a rectangle
c) an ellipse
Question 3: Draw the medial axis of
a) a circle
b) a square
c) a rectangle
d) an equilateral triangle
Question 4: Give the smallest number of statistical moment descriptors needed to
differentiate between the signatures shown in slide 14.
Question 5: Give two boundary shapes that have the same mean and third statistical
moment descriptors, but different second moments
Question 6: Obtain the grey-level co-occurrence matrix of a 5x5 image composed of
a checkerboard of alternating 1’s and 0’s if
a) the position operator is defined as “one pixel to the right” and
b) “two pixels to the right”.
Practical Assignments
Question 7: Try the function cad cod that produces the chain code of a connected
component in a image. Draw a simple small image, run “cadcod” and check if you
agree with the result.
Question 8: Try the function splitmerge that implements the split and merge
algorithm. Test your program with the binary image from bola.bmp. Visualize what
happens when you use different values for the maximum distance.
Question 9: Try the function assinaang that produces a signature angle  distance to
centroid. To test the function, generate a binary image with the form of a square or a
circle. Do you agree with the results?
Question 10: Read the help of the funcion “regionprops” of MATLAB. Take a
satellite image and segment it using the watershed based program shown in a previous
chapter. Then compute some form features of the resulting segments.
Question 11: Write a function that gets the chain code as produced by the function
“cadcod” and generates the corresponding image. Try with the sequence:
Chain= [ 0 0 0 7 5 4 4 2 4 2];
Question 12: Read the help of the function fourierdesc that computes the Fourier
descriptors and the function invfourierdesc . Verify how the reduction of descriptor
Representation and Description
affects the shape of an object. Use the function “roipoly” from MATLAB to draw
some test images.
Question 13: Read how the function invmoment works. Write a MATLAB script that
reproduces the same example shown in classroom slides.
Question 14: Use the function given here and compute the n first Haralick texture
features of each sample of the 5 available types of Brodatz textures. Build 2 dimensional
scatter plots for each pair of Haralick features where each texture type is marked with a
different color or symbol (see example below). Is there a pair of attributes that could be
used to separate these texture types sharply? Hint: use the MATLAB function plot
xb
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