Talal Itani said:Hello,
I am trying to understand the purpose of the rasterizer. Why do some
printers have a rasterizer, and others do not?
Thanks.
ALL printers have a "rasterizer" (raster image processor, also RIP).
Maybe it's inside the printer, maybe it's in the driver that resides on
(and uses the processing power of) your computer.
The laser engine must be told where to image dots and where not to image
dots on the drum. That dot pattern is a raster pattern. Something
builds that raster pattern. The raster image processor builds that
raster pattern.
A RIP can be in your driver, it can be inside the same case as the laser
engine itself, or it can be outside the case as a separate, standalone
unit.
The purpose of a "rasterizer" (RIP) is to make the dot pattern that
tells the imaging drum where to pick up toner and where not to pick up
toner.
Make sense?
Talal Itani said:Your explanation brings another question:
'why do some printers require a dedicated RIP box?'
Well, understand that the "rasterizer" is always a separate computer
dedicated to the task of rasterizing. Some printers depend on your host
Windows/Macintosh computer to do the raster processing, others install
the RIP computer inside the same case with the laser engine, and others
place the RIP computer outside in its own case.
But in every case, there's a separate RIP. In two of the three cases
above, it's a dedicated RIP.
In high end situations, you want to separate the RIP from the engine.
In all cases the output of the RIP is a raster pattern that the engine
can use, but inside the RIP can have many different features. To
facilitate giving the customer what he wants, it's far easier to let him
pick and choose the RIP features separate from the engine features.
Most, if not all, modern inkjet printers simulate the very high dpi
figures they quote by varying the amount of ink deposited at a given
location (hence the change in dot size). The actual hardware resolution,
as defined by the distance between dot centers is often much lower (eg
600dpi rather than 2400dpi).
AFAIK, Laser printers, however, only quote the actual hardware resolution
as they're unable to vary the amount of toner at a given location - it's
an all-or-nothing affair.
cmyk said:Hi Talal,
Changing the RIP won't improve you printer's performance in this area.
Most, if not all, modern inkjet printers simulate the very high dpi
figures they quote by varying the amount of ink deposited at a given
location (hence the change in dot size). The actual hardware resolution,
as defined by the distance between dot centers is often much lower (eg
600dpi rather than 2400dpi).
AFAIK, Laser printers, however, only quote the actual hardware resolution
as they're unable to vary the amount of toner at a given location - it's
an all-or-nothing affair.
Talal Itani said:So, with a LaserJet, the advertised DPI is true DPI, right?
cmyk said:AFAIK, Laser printers, however, only quote the actual hardware resolution as
they're unable to vary the amount of toner at a given
location - it's an all-or-nothing affair.
Changing the RIP won't improve you printer's performance in this area.
Most, if not all, modern inkjet printers simulate the very high dpi
figures they quote by varying the amount of ink deposited at a given
location (hence the change in dot size). The actual hardware resolution,
as defined by the distance between dot centers is often much lower (eg
600dpi rather than 2400dpi).
AFAIK, Laser printers, however, only quote the actual hardware resolution
as they're unable to vary the amount of toner at a given location - it's
an all-or-nothing affair.
Torbjorn Lindgren said:Not necessarily, most or all modern laster printers are also capable
of varying the amount of toner, though more often than not they
document the "real" resolution in addition to the simulated one.
There was a period when it was only inkjets that did this but stopped
many years ago (5+ years IIRC). My understanding is that lasers tends
to have less different spot sizes than inkjets (3-5 instead of 10 or
more).
However, most lasers do seem to list both their "native" resolution
and the higher "up to" figures, inkjets often requires quite a bit
more digging to find out the real HW dpi, so it IS different.
Real laser printer resolution is often 600x600/600x1200/1200x1200,
though there's still some older 300x300 or 300x600 models out there in
the lower end (ick).
As an example most recent B&W HP LaserJets seems to have "HP FastRet
1200" and "up to 1200x1200 dpi". That's the only thing they list for
their lower & mid-range printers, while the bigger ones says that and
notes the real resolution is 600x600 dpi.
HP's color lasers seems to be a mix of 600x600 and 600x1200, with HP
ImageREt 3600 (most) or HP ImageREt 4800 (some but not all of the
600x1200 models), there's some additional tricks that can be done on
color images.
OKI and Lexmark seems to be operating with similar resolution figures,
though both are better at printing the native resolution than HP is
(it's on all models I saw). Samsung doesn't seem to have usefull
specifications on their printers at all...
Talal Itani said:I need to achieve 2400 x 2400 dpi.
Why?
...
I am printing tiny text, called micro text, or microscopic text. An
imagesetter at 2400 dpi does it well, but it is an expensive solution.
Well yeah... of course it is, why would you expect it to be cheap?
I wouldn't consider an imagesetter to fall into the competive mass
market category.
Talal Itani said:Inkjet printers, like the Canon I have, have a
resolution of 4800 x 2400 dpi. When I use a loupe, I can see the very very
tiny dots. The dots are tiny when the colors are light. When the colors
are dark, the high-resolution is not maintained.
It depends how small the text, the kind of material on which it is
printed, and the font used.
As an experiment ! printed a range of sizes from 1 point to 2 points on a
Xerox 2025 at 1200 x 1200 genuine set at 120 lpi.
On uncoated papeer 1 point is illegible and 1.5 is readable under the
loupe.
On coated paper 1 point is readable under the loupe using a bold font.
Xerox has produced a MicroText system to 'print' at 1/100 of an inch for
security douments so I assume 0.75 point is the size to emulate.
Would microfilm techniques be another method?
Aandi Inston said:I wonder if you are seeing halftone dots. Some inkjets will use
halftones, others dithering. Where halftones are used you will see
dots that grow from very small to large and eventually join. The
separation of these dots is the "lpi" value, and probably something
like 150-200. This is the effective resolution of color detail. The
finest colour detail, in highest quality professional printing, is
probably around 300 lpi (wild guess).
However, it's worth noting that, unlike many lasers and imagesetters,
the high resolutions quoted for inkjets are nominal; 2400 dpi does not
imply a smallest possible dot of 1/2400 inch.
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What about digital printing presses that are advertised as 2400 x 2400 dpi?
These are the big machines, made by Xerox, Oce, Indigo, and a few others.