This image has been created by replacing each pixel in a high contrast image by either a white or a red spot. The geometry is such that the spots are separated by exactly one radius.
The above image is a jpg. It was created however from a vector image in which the spots are perfect. You can see this for yourselves by opening the pdf file onecup.geo.pdf and zooming in. You will see that the spots are perfect.
Alternatively, just look at this blow-up of part of the image, which gives you the general idea.