This is an image with transparency. It is used because it is a difficult one and show the limitations of each method.
The image several tones of grey near to white, which makes error diffusion more difficult
If the background is not white, it can be perceived that the array dithering don't fill the upper left circle, this is a consequence of the image scan method.
It can be observed that the serpentine scan remove some artifacts in dithers with less diffusion like Floyd-Steinberg, but also creates vertical artifacts sometimes.
