undefined function or method of type char

below is the link to my question. It is the first one listed on the homework in regards to image processing. Below it what I have started to but I keep getting an undefined function or method error of type char, any help or advice would be great!

http://www.cse.ohio-state.edu/~raghu/teaching/CSE205/HW/CSE205_HW6.pdf

funnyflag_2

for i = 1,32;
    for j = 1,22;
        r(i,j) = 1;
        g(i,j) = 0;
        b(i,j) = 0;
    end
end

for i = 1,32;
    for j = 23,46;
        r(i,j) = 0;
        g(i,j) = 1;
        b(i,j) = 0;
    end
end

for i = 1,32;
    for j = 47,66;
        r(i,j) = 0;
        g(i,j) = 0;
        b(i,j) = 0;
    end
end

for i = 33,64;
    for j = 1,22;
        r(i,j) = 0;
        g(i,j) = 1;
        b(i,j) = 0;
    end
end

for i = 33,64;
    for j = 23,46;
        r(i,j) = 0.5;
        g(i,j) = 0.5;
        b(i,j) = 0.5;
    end
end

for i = 33,64;
    for j = 47,66;
        r(i,j) = 0;
        g(i,j) = 0;
        b(i,j) = 1;
    end
end

r = c(:,:,1);
g = c(:,:,2);
b = c(:,:,3);
c = cat(3,r,g,b);
colormap(c);
image(myimage)

Answer 1

[the cyclist]

Is this the entire code? If so, then one problem is that when you get to this line:

r = c(:,:,1);

you have not yet defined the variable c, so MATLAB can't make the assignment.

[Matthew]

This is the entire code, i ordered the last few lines so c is defined and changed the image line so it reads

c = cat(3,r,g,b);

r = c(:,:,1);

g = c(:,:,2);

b = c(:,:,3);

colormap(c);

image(c)

but i am getting a colormap error now, and it says that color map must have three columns [R G B]

I guess what im trying to do is define a vector of nxm and allocate specific colors intro a matrix to get the image posted in the link. Im really confused what else I should tweak?

[the cyclist]

You don't need the colormap step. The image() function is going to take care of that for you. Leave that out.

Then, make the change that Sean and Walter mentioned, replacing all the for loops with code like i=1:32 rather than i=1,32.

If you do that, then your code is like this:

for i = 1:32;

for j = 1:22;

r(i,j) = 1;

g(i,j) = 0;

b(i,j) = 0;

end

end

for i = 1:32;

for j = 23:46;

r(i,j) = 0;

g(i,j) = 1;

b(i,j) = 0;

end

end

for i = 1:32;

for j = 47:66;

r(i,j) = 0;

g(i,j) = 0;

b(i,j) = 0;

end

end

for i = 33:64;

for j = 1:22;

r(i,j) = 0;

g(i,j) = 1;

b(i,j) = 0;

end

end

for i = 33:64;

for j = 23:46;

r(i,j) = 0.5;

g(i,j) = 0.5;

b(i,j) = 0.5;

end

end

for i = 33:64;

for j = 47:66;

r(i,j) = 0;

g(i,j) = 0;

b(i,j) = 1;

end

end

c = cat(3,r,g,b);

% r = c(:,:,1);

% g = c(:,:,2);

% b = c(:,:,3);

figure

image(c)

I think you will find that you are getting closer to what you meant to do. (But not quite there yet.)

Answer 2

[Sean de Wolski]

instead of 1,32 or 33,64, the comma (',') should be a colon (':');

doc colon

for more info

Answer 3

[Walter Roberson]

for i = 1,32;

is not the correct way to write a "for" loop over a range of values.

You do not indicate which line is complaining about undefined function or variable ?

Answer 4

[Walter Roberson]

A colormap is not a 3D array: it is an N x 3 array, where N is the number of entries in the color map. For example, 256 x 3. The first column is red values, the second column is green values, the third column is blue values.

Remember, colormaps are row indexed by color numbers to determine the color to associate with a point for a pseudo-color plot. A pseudo-color plot has a single number for each point that is used for that row index, not a pair of numbers used for x-y indices.