[XeTeX] XeLaTeX resolution

[Taco Hoekwater]

Steve Peter wrote:
> On Feb 23, 2009, at 4:44 PM, Meho R. wrote:
> 
>> I read somewhere that resolution of 267 dpi for bitmap images is  
>> enough. Can anyone confirm it?
> 
> Printers usually request 300 dpi.

This is because of the way halftoning works: the rasterizing hardware
generally operates at somewhere between 80 and 200 "lines per inch"
(lpi), where each of those "lines" represents a row of color values,
each of which is stashed in a grid of dots (e.g. 16x16) that can be
on or off to create particular shades of ink. So 50% black means
that half of the dots in a grid are "on" == ink on paper (I am
simplifying a little)


The asked resolution for images always has to be a bit (1.5-2) higher
than the lpi value used, to avoid various resampling artifacts, but
there is no point in going much higher because the precision will be
lost anyway.

So 300dpi is typical for greyscale images at their natural size
(photographs often look acceptable at even lower resolution but
that is mostly because complex imagery that itself help counteract
artifacts). You have to watch out for image scaling, of course.

The required resolution for line art (= black&white bitmaps) is
much higher. The difference between 1200dpi and 2400dpi line drawings
in the printed result is still easily noticeable, and anything using
less than 600dpi will look a bit cheap and out of place in comparison
to the crisp font shapes on the rest of the printed page.

Best wishes,
Taco