Several questions about halftoning

1. What kind of effects for haltoning is perfect(or for printing)?--blue-noise property? What's an interesting halftoning?

2. Density means? Density and harmonity?

3. The constrast for halftoning?

4. Maintain the original structure

5. The pattern creation(means new pattern): how to deal with the original structure or pattern?

6. What do you think about the above image?

Another more related paper: digital halftoning with space filling curves by Velho and Gomes; and some halftoning by fractal path