Filmscanners mailing list archive (firstname.lastname@example.org)
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RE: filmscanners: pixels, printer dots, etc
> On page 67 of that book he shows a tiny 32 pixel image scaled to 5
> dpi. It's printed as a 6.4 inch graphic with pixels that are,
> obviously, 1/5 inch in size. My question is, what does this say about
> print resolution?
> The printer is obviously using a certain number of
> dots to produce one pixel.
> Is this number of dots specified simply by
> selecting the print resolution in the printer driver menu?
To some degree, yes. If the printer driver is using a typical halftone cell
to do halftoning, the cell is typically square...and it gets "filled in"
with a particular number of dots that represent a % gray level. So, if you
had a halftone cell say 4x4, that occupies 16 printer dots...and if you had
half the dots black, and half of them not black, then you would have
Now, on to printer resolution...if you print at 720 DPI, that will take up
four times as large an area for each halftone cell than if you printed at
1440 (2x in each direction).
Typically, newer printer drivers don't use typical fixed halftone cells, but
variable cell sizes, as well as "random" (stochastic) dithering. Why I say
above to some degree, is that there are other factors, like how many tones
you want to represent...more tones requires more area, and the halftone
algorithm can also factor into the determination.