Re: re hp designjet 50ps
Re: re hp designjet 50ps
- Subject: Re: re hp designjet 50ps
- From: Tom Beckenham <email@hidden>
- Date: Wed, 28 Nov 2001 10:53:48 +1100
Yes that helps enormously. I was confused by the 6 color thing. Printer
manufacturers market their printers as 6 color devices. There was also quite
a bit of talk a while back about profiling Epson inkjets as RGB devices. How
is the hp different from the Epson in terms of profiling? Why would you
profile them differently? Or is that wrong to profile an Epson as an RGB
device.
I'm still looking for better info on the Heidelberg RIP. And yes I've looked
at the hp site - there is tech specs on the printer but little on the RIP.
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From: Henrik Holmegaard <email@hidden>
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Date: Tue, 27 Nov 2001 09:28:38 +0100
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To: email@hidden
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Subject: re hp designjet 50ps
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>
email@hidden wrote:
>
>
> Is this a "real" 6 color printer ie do you
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> create a 6 color profile and send 6 components/plates to it from your RIP.
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> Or is it like the Epson 6 color printers where you can't actually control
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> the 6 colors individualy and would usually create an RGB profile for it
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> instead of a CMYK or CcMmYK. Also, I can't find any info on the Heidelberg
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> RIP that comes with the 50 ps or is it really an hp RIP? Can you send
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> pre-converted files through the RIP without any further "correction" in the
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> RIP.
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>
To be suitable as prepress proofers, inkjets should use light cyan
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and light magenta. The larger elementary spot size of inkjets
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compared to an offset press benefits from building highlights with
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light cyan and light magenta. The light cyan and light magenta inks
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have a lower optical density than the cyan and magenta inks, so you
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are going to be laying down a bit more ink in the highlights.
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CcMmYK printing is not like hifi printing, if that is what you mean.
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You are looking at four channels and not six. The step from four to
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six channels is handled in firmware after the step from three
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channels into four channels in Photoshop / Illustrator / InDesign.
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Thus CcMmYK printers present a CMYK interface.
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CcMmYK printers are fed through two basic types of printing pipeline,
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Mac OS QuickDraw / Windows GDI which accepts only three channel RGB
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objects in the printing stream, and PostScript which accepts RGB,
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CMYK, Grayscale, Lab and custom color spaces in the printing stream.
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Thus the number of ink cannisters in the printer is separate from the
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number of channels supported in the printing pipeline that feeds the
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printer.
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To use a CcMmYK printer for prepress proofing, you want to use the
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PostScript printing pipeline (which is application level only) and
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not the RGB-only OS pipeline. For a CcMmYK printer fed through the
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PostScript printing pipeline, you use a CMYK printer target and not
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an RGB printer target. Some RIPs will limit ink for you, others will
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let you manage the ink limiting manually. Ink limiting should be done
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prior to printing the CMYK test chart, just as on a press you run to
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optimal density before printing the test chart.
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When the test chart is printed, set the profile to 400% total ink. Do
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not as on an offset press lower the total ink in the profile and / or
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set a high black replacement throughout the inkjet color space. An
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inkjet does not require black replacement for color stability, and
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black replacement in highlights and midtones (as with GCR set to a
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high start) will introduce peppercorn / grain in the screening.
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Hope this helps.
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