[softwarelist] Re: Really, really 'Colour printing from OvPro'
- From: Peter Newble <peter@xxxxxxxxxx>
- To: davidpilling@xxxxxxxxxxxxx
- Date: Sun, 22 Jul 2012 01:00:08 +0100
On 22 Jul 2012, at 0045, David Pilling wrote:
> Thought occurred to me, some printers have problems with the screening code
> OP adds to the PS output stream. Turn off screening is the solution.
Good point. Getting a limited range of colours, with too much saturation,
implies too high a screen resolution. For instance, a 300lpi screen on a 600dpi
device only gives you four possible on-off states (2×2) per colour plane,
whereas a 75lpi screen on the same 600dpi device gives you 256 (8×8) and thus a
finer gradation of shades of each colour. Either the PDF conversion is removing
a high screen setting specified in the original PS output, giving a better
result, or perhaps the printer has a default high screen setting which printing
straight from OP to the RISC OS PS driver isn’t overriding, but something in
the PDF conversion is replacing it with something more sensible.
My early laser printers all used a dot screen, and getting the right setting
for each job was quite tricky, given that the pixel resolution of the printers
was so much lower than that of an imagesetter. I might be wrong, but modern
printers appear to use stochastic screening where the concept of a screen
ruling doesn’t exist – but perhaps it can be enabled if the Postscript
specifies it. No doubt Martin Wuerthner will know more about this . . .
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