Large drawing (Hal) with nested squares

One issue with my simple drawing tools is that, for the most part, the mark produced is uniform in width and color (one exception is a brush. The brush can be pushed into the surface to make a thicker mark or pulled out to leave a thinner one). It occurred to me that, already having the ability to determine the value (lightness or darkness) of any area of some reference image, I could draw a square spiral with more or fewer revolutions (I think of this quality as drawing a tighter or looser spiral) to communicate any given value.

My ShopBot CNC can, in two commands, draw nested rectangles of any dimension and offset. By offset, I mean the (the distance between each successive nested rectangle). The first command sets the offset and the second command draws the nested rectangles. So my first program accepted parameters from me at run-time (parameters included the location of the reference image, the dimensions of the drawing to be made, the size of the rectangles (in this program these were always square) to be drawn, the minimum offset (densest spiral) and off we go!

The first effort was an enormous (98 x 52 inches) pen and ink drawing of my friend, Hal Wert, author, historian, professor, good guy. I worked on this drawing repeatedly for weeks, ultimately surrounding it with smaller studies as I refined my program and my technique, no longer relying on the built-in rectangle code of my machine – instead I coded a very versatile spiral generation (which continued to use for several more years).