Show a basic storage type to handle a simple RGB raster graphics image,
and some primitive associated functions.

If possible provide a function to allocate an uninitialised image,
given its width and height, and provide 3 additional functions:

   one to fill an image with a plain RGB color,
   one to set a given pixel with a color,
   one to get the color of a pixel.


(If there are specificities about the storage or the allocation, explain those.)

These functions are used as a base for the articles in the category raster graphics operations, 
and a basic output function to check the results
is available in the article write ppm file.




im = zeros(W, H, 3, "uint8"); % create an RGB image of width W and height H
                              % and intensity from 0 to 255; black (all zeros)
im(:,:,1) = 255;              % set R to 255
im(:,:,2) = 100;              % set G to 100
im(:,:,3) = 155;              % set B to 155
im(floor(W/2), floor(H/2), :) = 0;  % pixel in the center made black
disp(im(floor(W/3), floor(H/3), :)) % display intensities of the pixel
                                    % at W/3, H/3
p = im(40,40,:); % or just store it in the vector p, so that
                 % p(1) is R, p(2) G and p(3) is B