Re: ColorPort and target precision
Re: ColorPort and target precision
- Subject: Re: ColorPort and target precision
- From: "Roberto Michelena" <email@hidden>
- Date: Mon, 5 Jun 2006 00:23:34 -0500
Are you suggesting that you create targets with dithering? That seems
like a really bad idea to me.
The really best thing to do is have vector targets with exact values,
if we're going to feed them into a proofing rip with a good internal
architecture that will render them exactly.
BUT, given that such is not always the case...
Take for example 5% ; if you create an 8-bit TIFF it ends up being
4.7059% (value 12/255), an error of 0.29% which is 6% of the original
value. Granted it doesn't sound as much, but why have it so if we can
do things better?
We can instead make a checkerboard of values 12 and 13, which would
yield a patch of 12.5/255=4.902% ; any printer driver or RIP will take
this (both) pixel values into account when rendering the
stochastically screened patch, and any instrument will read them as
one because the dithering is much smaller than the instrument's
aperture, even if we do it at 72dpi.
And if we want to sophisticate, we can mix in one value of 14 in
replacement of a 13, every 4 pixels. Then we would get
(12*2+13+14)/4=12.75 ; 12.75/255= 5% exactly.
And 4 pixels at 72dpi is still quite inside the instrument's aperture,
which is at least about 56 pixels at 72dpi (3mm circle). Not to
mention the fact that most scanning instruments (EyeOne, DTP41, etc)
take multiple readings over their passing across the patch.
So we're quite safe dithering our 8-bit targets at 72dpi in order to
get exact values.
best regards,
-- Roberto Michelena
Infinitek
Lima, Peru
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