a) An image constructed from the average flux densities of the input sources to the simulation. b) The dirty image. c) The result of 2000 cycles of Högbom clean at a loop gain of 0.1. d) The result of a Sault-Wieringa clean (with the same niter and loop gain) as described in the text. The unsaturated brightness range for all four images was  − 0.02 to +0.02 Jy/beam. (For comparison purposes, the brightest pixel of the source image was 1.27 Jy/beam.) The grey scale is reversed. Black rectangles indicate the area chosen for the rms measurement as described in the text.