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.




img = Image[ConstantArray[{1, 0, 0}, {1000, 1000}]];
img = ReplacePart[img, {1, 1, 1} -> {0, 0, 1}];
ImageValue[img, {1, 1}]