How to generate sinusoidal color fringes in MATLAB??

Hi. I am new to MATLAB, Can any one help me in getting the solution. I'm attempting to generate sinusoidal color fringe patterns, using MATLAB.

I'm struggling to find a way in which i can go about generating color fringes as shown in the below figure.

Any help would be appreciated,

Thanks.

Answer 1

[DGM]

It's not clear to me how these are sinusoidal or even periodic.

You can simply create an image like the one shown, but if you want some particular calculated pattern, it's up to you to explain the thing you're trying to create.

CT = [1 0 0; 0 1 0; 0 0 1]; % a colormap

% generate indexed color image as a vector
fringe = [3 1 2 1 3 2 3 1 2 3 1 2 3 1 3 2 1 2 3 1 2 3 2 1 2 3 1 3 2 3 1 3 1 2];

% expand the vector into a 2D image
blocksize = [50 10]; % [y x]
fringe = imresize(fringe,blocksize.*size(fringe,1:2),'nearest');

% convert to RGB
fringe = ind2rgb(fringe,CT);

% show it
imshow(fringe)

[LALITHA SREE]

i want to generate sinusoidal fringes each with a single color like Red, Green, and Blue with different phases. And add these different patterns to form a single fringe pattern.

i tried the below code, but i don't want to use colormap here. If i use colormap, while adding i am unable to get colored fringes as Red, Blue, Green. can you please check the below code, it would be helpful.

Thank you.

center = [0,0]; %[0,0] is the middle of the image, [pi,pi] is the lower right

orientation =pi; %radians (pi/4 = 45 degrees)

width = .5;  %1/e half width of Gaussian

spatialFrequency = 10;  %spatial frequency of Sinewave carrier (cycles/image)

phase = pi;     %spatial phase of sinewave carrier (radians)

contrast = 1;   %contrast ranges from 0 to 1;

n = 201;        %resolution of the image

[X,Y] = meshgrid(linspace(-pi,pi,n)); % Use meshgrid to define matrices X and Y that range from -pi to pi;
ramp = cos(orientation)*(X-center(1)) + sin(orientation)*(Y-center(2));
sinusoid1 = contrast*sin(spatialFrequency*ramp-phase);
figure(1)
imagesc(sinusoid1)
mymap1 = [1 0 0
    1 1 1
    1 0 0
    1 1 1
    1 0 0];

colormap(mymap1);

axis off;axis equal ;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
phase2 = pi/2;
sinusoid2= contrast*sin(spatialFrequency*ramp-phase2);
figure(2)
imagesc(sinusoid2)

mymap2 = [0 1 0
    1 1 1
    0 1 0
    1 1 1
    0 1 0];

colormap(mymap2);
axis off; axis equal; 

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
phase3 = 2*pi;
sinusoid3= contrast*sin(spatialFrequency*ramp-phase3);
figure(3)
imagesc(sinusoid3)

mymap3 = [0 0 1
    1 1 1
    0 0 1
    1 1 1
    0 0 1];

colormap(mymap3)

axis off; axis equal;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% adding all three color fringes

addedgrating= sinusoid1+sinusoid2+sinusoid3;
figure(4);
imagesc(addedgrating);
axis off; axis equal;

[DGM]

You have three images with sinusoidal profiles. They're colormapped such that they are colored (R,G, or B) at -1,0 or 1, otherwise they're white.

Adding the RGB images will result an image which contains no R,G, or B bars, so obviously adding in RGB isn't what's intended. Note that adding will obviously result in image data being out of range, hence the normalization.

Rgrat = ind2rgb(gray2ind(sinusoid1,5),mymap1);
Ggrat = ind2rgb(gray2ind(sinusoid2,5),mymap2);
Bgrat = ind2rgb(gray2ind(sinusoid3,5),mymap3);

sumgrating = Rgrat + Ggrat + Bgrat; % add
sumgrating = mat2gray(sumgrating); % normalize

imshow(sumgrating)

It's all white and secondary colors, as obviously there's a lot of primaries and white being added to each other. If you inverted it, you might get something with primaries and black, but that's nothing like the example either.

Adding the original sinusoidal images will result in an image which is the sum of the sinusoids, but how that's colormapped to contain R,G,and B is yet unknown. If I were to just make something up:

% however long you want the map to be
CT = [1 0 0; 0 1 0; 0 0 1; 0 1 0; 1 0 0];
rgb = ind2rgb(gray2ind(addedgrating,size(CT,1)),CT);
imwrite(rgb,'rgb.png')

... but that's just me guessing.

[LALITHA SREE]

@DGM Thank you

Actually i want to generate colored fringes like below, can you help me out

[DGM]

Oh. So something more like this:

% parameters
center = [0,0]; %[0,0] is the middle of the image, [pi,pi] is the lower right
orientation = pi; %radians (pi/4 = 45 degrees)
width = .5;  %1/e half width of Gaussian
spatialFrequency = 10;  %spatial frequency of Sinewave carrier (cycles/image)
phase = pi;     %spatial phase of sinewave carrier (radians)
contrast = 1;   %contrast ranges from 0 to 1;
n = 201;        %resolution of the image

[X,Y] = meshgrid(linspace(-pi,pi,n)); % Use meshgrid to define matrices X and Y that range from -pi to pi;
ramp = cos(orientation)*(X-center(1)) + sin(orientation)*(Y-center(2));

sinusoid1 = contrast*sin(spatialFrequency*ramp-phase);

phase2 = pi/2;
sinusoid2 = contrast*sin(spatialFrequency*ramp-phase2);

phase3 = 2*pi;
sinusoid3 = contrast*sin(spatialFrequency*ramp-phase3);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% create the grating images as RGB images
Rgrating = (sinusoid1 + 1)/2.*permute([1 0 0],[1 3 2]);
Ggrating = (sinusoid2 + 1)/2.*permute([0 1 0],[1 3 2]);
Bgrating = (sinusoid3 + 1)/2.*permute([0 0 1],[1 3 2]);

sumgrating = Rgrating + Ggrating + Bgrating;
montage({Rgrating, Ggrating, Bgrating, sumgrating})

Or if you didn't need the individual gratings for anything else, you could simplify everything:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% create the final grating image without the individual colored gratings
sumgrating = (cat(3,sinusoid1,sinusoid2,sinusoid3)+1)/2;
imshow(sumgrating)

[LALITHA SREE]

@DGM Thank you, It is very helpful.