Initialize the arrays as follows:

As you can see, we are initializing the first array to zeroes. The other arrays are initialized with functions from the numpy.random package that generate random integers.

The next step is to generate squares. We create the squares using the arrays in the previous step. With the clip function, we will make sure that the squares do not wander outside the image area.

The meshgrid function gives us the coordinates of the squares. If we give this function two arrays with size N and M, it will give us two arrays of shape N by M. The first array will have its elements repeated along the x axis. The second array will have its elements repeated along the y axis. The following example of an IPython session should make this clearer:

In: x = linspace(1, 3, 3)

In: x
Out: array([ 1.,  2.,  3.])
In: y = linspace(1, 2, 2)

In: y
Out: array([ 1.,  2.])

In: meshgrid(x, y)
Out: 
[array([[ 1.,  2.,  3.],
      [ 1.,  2.,  3.]]),
 array([[ 1.,  1.,  1.],
      [ 2.,  2.,  2.]])]

Finally, we will set the colors of the squares:

for i in xrange(NSQUARES):
   xindices = range(centers[i][0] - radii[i], centers[i][0] + radii[i])
    xindices = numpy.clip(xindices, 0, N - 1)
    yindices = range(centers[i][1] - radii[i], centers[i][1] + radii[i])
    yindices = numpy.clip(yindices, 0, N - 1)

    if len(xindices) == 0 or len(yindices) == 0:
      continue

    coordinates = numpy.meshgrid(xindices, yindices)
    img[coordinates] = colors[i]

Before we load the image data into a memory map, we need to store it into a file with the tofile function. Then, we load the image data from this file into a memory map with the memmap function:

img.tofile('random_squares.raw')
img_memmap = numpy.memmap('random_squares.raw', shape=img.shape)

To demonstrate that everything worked fine, we will display the image with Matplotlib:

matplotlib.pyplot.imshow(img_memmap)
matplotlib.pyplot.axis('off')
matplotlib.pyplot.show()

Notice that we are not displaying the axes. The following is an example of a generated image: