Scilab Basics-activity 2

Scilab is a programming language that makes it easy for one to deal with array and matrices. Its commands makes problems with matrices very easy to tackle. In this activity we were asked to make synthetic images to test algorithms and to see if we understood the basic commands in Scilab.

The first image that was made was a circle aperture. This was given as an example to us. The code is shown below.

Circle Aperture


[1] nx = 100; ny = 100; //defines the the number of elements along x and y
[2] x = linspace(-1,1,nx); //defines the range
[3] y = linspace(-1,1,ny);
[4] [X,Y] = ndgrid(x,y); //creates two 2D arrays with x and y coordinates
[5] r= sqrt(X.^2 + Y.^2); //note element-per-element squaring of X and Y
[6] A = zeros (nx,ny);
[7] A (find(r<0.7) ) = 1;
[8] imshow (A, []);

The image generated from this code is shown below.

Fig. 1 Image of the circle aperture generated using Scilab

I used lines 1 to 4 from the sample code to create the arrays for all of the images generated here.

Annulus

To create the annulus, I used the lines 1 to 6 from the code to generate the circle aperture. I then add lines 7 -11 below. This was done to generate an outer and inner circle for the annulus.

[7] ro = 0.8; //radius of outer circle

[8] ri = 0.4; //radius of inner circle

[9] A(find(r<ro)) = 1;

[10] A(find(r<ri)) = 0;

[11] imshow(A, []);

Fig. 2 Image of the annulus generated using Scilab

Circular aperture with graded transparency

To create the circular aperture with graded transparency, I once again used lines 1 to 6 from the code to generate the circle aperture. I add to the code lines 7-8 since I assumed a gaussian distribution for the beam and multiplied the matrix of the circular aperture with it. 

[7] G = exp(-4*X.^2 - 4*Y.^2); //gaussian multiply to matrix

[8] imshow(G,[]);

Fig. 3 Image of the circle aperture with graded transparency generated using Scilab

Centered square aperture


I added lines 5-8 to generate the aperture. The side was set to 0.3
[5] A = zeros(nx,ny);
[6] s = 0.3; //sets the length of a side
[7] A(find(abs(X) <s & abs(Y)<s))=1;
[8] imshow(A, []);

Fig. 4 Image of the centered square aperture generated using Scilab

Sinusoid along the x-direction (corrugated roof)


I added lines 5-10 tp set the amplitude and frequency for the sinusoid and restricted it to zero and positive values to generate the sinusoid.

[5] A = zeros(nx,ny);
[6] a = 3; //sets the amplitude of sinusoid
[7] f = 30; //sets the frequency of sinusoid
[8] A = a*sin(f*X);
[9] A = A + abs(min(A)); // restricts to non-negative values
[10] imshow(A, []);

Fig. 5 Image of the sinusoid along x-direction generated using Scilab

Grating along the x-direction 8 divisions

I add lines 5-10 to the code. What this does is divide the elements along x by 8 to produce a grating with 8 divisions.

[5] A = zeros(nx,ny);
[6] A(1:nx/8, 1:ny) = 1;
[7] A(2*nx/8:3*nx/8, 1:ny) = 1;
[8] A(4*nx/8:5*nx/8, 1:ny) = 1;
[9] A(6*nx/8:7*nx/8, 1:ny) = 1;
[10] imshow(A, []);

Fig. 6 Image of the grating generated using Scilab

For this activity, I would give myself a grade of 9/10. It was a little bit rushed so my presentation wasn't that great and very detailed but I did all the requirements. The image generated looked correct. I would like to thank Ma'am Soriano for the tip she gave me to make my scilab and sip toolbox work. I also looked at the Scilab hands on tutorial by satish annigeri.