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Author Topic: the deal with calib/linearz on HP Zs?  (Read 6337 times)
Haraldo
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« on: January 09, 2007, 10:07:47 PM »
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Last post of the day -- promise!

We were talking (who knows where now) about calibration, linearization, and all that stuff as it relates to the new HP Z printers and Epsons. Remember?

I was getting confused too, so here's the deal (from HP Engineering):

The new Zs both calibrate (maximum density or Dmax for each ink individually, minus GE) and linearize (linear response in colorimetric density as a function of input digital counts) whenever you want (this is rolled into the "calibration" function). As far as I know, Epson does not do this in the field (your printer in your place) but everyone assumes they do some form of both in the factory. The Zs also do this for each media individually, with different Dmax goals and for your current environmental conditions.

(so where's Canon in all this?)

Harald Johnson
author, "Mastering Digital Printing, Second Edition"
DP&I.com ( http://www.dpandi.com )
digital printing and imaging consultant
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Haraldo
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Stephen Best
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« Reply #1 on: January 09, 2007, 10:25:14 PM »
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In reality, not much different to what a (proper) RIP would do ... just automated. Epson's ColorBase normalizes the response for each paper. It's unclear whether the generated settings update the driver files, or the printer itself. Irrespective, it's useless with third-party papers as it has no data to normalize against.

Do you have to calibrate and re-profile after a head swap? I would imagine this would get pretty old fast in the busy environments these machines are destined/priced for.
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opgr
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« Reply #2 on: January 10, 2007, 02:30:54 AM »
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I was getting confused too, so here's the deal (from HP Engineering):


HP Engineering is totally confused as well then, and totally delusional too. Are you sure they knew they were talking to a knowledgeable person? This has all the characteristics of marketing crap.

Think about it:

1. There is no such thing as a spectrometer (or colorimeter) that can see craquelure, and overprint- or drying-artifacts, especially considering they don't allow enough drying time to begin with. And they don't print nearly enough patches to calibrate the Dmax.

2. What constitutes a "linear" response? (Think this one through really long please)

3. True profiling, especially for custom papers, would be profiling the CMYK output, not "colorcorrecting" the RGB input. At the very least it should include adjusting the graybalance.
(Not much use in calibrating the Dmax for primary colors, when combination colors leak off of the page because too much ink was sprayed).

The profiling option on the HP is useful, because it is highly automated and it ensures that the printer will behave consistent. For the average user, this is helpful. For most average printshops this is really helpful. But between "behaving consistent" and "producing a colormatch" there is an insurmountable void that even live humans have not been able to bridge, but oh sure, HP came down the mountain and have blessed humanity with its predictive spirit.

There's definitely room for completely automated color such as implemented in the HPs, especially considering the many printshops that are (still) completely oblivious to cm, and eventually the software will become increasingly smarter and will be able to automate more and more of the profiling process. But Dmax and linearization are not part of that process.
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Oscar Rysdyk
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Haraldo
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« Reply #3 on: January 10, 2007, 10:25:40 PM »
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... Do you have to calibrate and re-profile after a head swap? I would imagine this would get pretty old fast in the busy environments these machines are destined/priced for.

Yes, you're supposed to calibrate with any printhead change. You don't need to re-profile unless you want to. Calibration is 8-10 mins. Profiling is 15-20 mins. Automatic. Check your stocks!

Harald
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Haraldo
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Haraldo
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« Reply #4 on: January 10, 2007, 10:37:06 PM »
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Well, who got out of the wrong side of the bed here? ;-)

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1. There is no such thing as a spectrometer (or colorimeter) that can see craquelure, and overprint- or drying-artifacts, especially considering they don't allow enough drying time to begin with. And they don't print nearly enough patches to calibrate the Dmax.

Huh? You're losing me, dude. "craquelure"? Why would I expect to see that on a fresh print from an inkjet printer? And yes, you can adjust the drying time from printing to spectro scanning to whatever you want. 5 mins is the Auto default for busy people. Take a day, a week.

Quote
2. What constitutes a "linear" response? (Think this one through really long please)

A linear response is a linear response. 50% in, 50% out. No?

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3. True profiling, especially for custom papers, would be profiling the CMYK output, not "colorcorrecting" the RGB input. At the very least it should include adjusting the graybalance.
(Not much use in calibrating the Dmax for primary colors, when combination colors leak off of the page because too much ink was sprayed).

It IS profiling the CMYK output. What else would it be?

Are we talking about the same subject?

Harald
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Haraldo
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Stephen Best
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« Reply #5 on: January 10, 2007, 10:51:40 PM »
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Yes, you're supposed to calibrate with any printhead change. You don't need to re-profile unless you want to. Calibration is 8-10 mins. Profiling is 15-20 mins. Automatic. Check your stocks!
[a href=\"index.php?act=findpost&pid=95029\"][{POST_SNAPBACK}][/a]

So if you calibrate with HP Glossy (or whatever) the calibration will apply to (say) Photo Rag? I'm just trying to get a handle on what the calibration actually does, and how it's different to per-media linearization.
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jclacherty
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« Reply #6 on: January 10, 2007, 11:41:34 PM »
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I'm just trying to get a handle on what the calibration actually does, and how it's different to per-media linearization.
[a href=\"index.php?act=findpost&pid=95032\"][{POST_SNAPBACK}][/a]

I think you'll find that calibration is media independent.  It is calibrating the printer to a known standard (which would be why it only accepts HP Adv Gloss) so that when the printer driver asks for 10% black, 40% Magenta etc. the same amount of ink comes out regardless of which machine you print on.  Profiling and calibration are different.  Ideally, if you have two machines which have been calibrated to the same standard then the same paper profile should produce identical results on both printers.

Justin.
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ericstaud
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« Reply #7 on: January 10, 2007, 11:59:45 PM »
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So if you calibrate with HP Glossy (or whatever) the calibration will apply to (say) Photo Rag? I'm just trying to get a handle on what the calibration actually does, and how it's different to per-media linearization.
[a href=\"index.php?act=findpost&pid=95032\"][{POST_SNAPBACK}][/a]

I am just starting to use Epson's ColorBase.  Just an FYI... ColorBase makes a seperate calibration for each of Epson's paper types.  So, the whole process could be time consuming and require one ink change from Glossy to Matte.  There a 9 paper choices, so you print and measure 9 charts (or just print the charts for papers you use).  It seems that after you calibrate several "like" printers and profile just one of them, that you could then use the one profile on all the printers that have been calibrated (saving a lot of time, paper, and ink).  Just thought this would be of interest in the this HP discussion.
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Stephen Best
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« Reply #8 on: January 11, 2007, 01:38:52 AM »
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I think you'll find that calibration is media independent.  It is calibrating the printer to a known standard (which would be why it only accepts HP Adv Gloss) so that when the printer driver asks for 10% black, 40% Magenta etc. the same amount of ink comes out regardless of which machine you print on.
[a href=\"index.php?act=findpost&pid=95040\"][{POST_SNAPBACK}][/a]

OK, now I understand. There must be a per-media linearization as well, namely to determine ink loading etc. Michael's first-look review seems to confuse calibration with linearization: "The process of creating a profile has two steps; calibration and profiling". Or is there separate printer calibration and media calibration?
« Last Edit: January 11, 2007, 01:47:52 AM by Stephen Best » Logged
BernardLanguillier
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« Reply #9 on: January 11, 2007, 01:52:08 AM »
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My guess was that:

- Calibration/linearization is the same thing: it is done on a paper whose characteristics are known, and the game is to figure out the amount of ink to inject through the head to reach targeted RGB values on that given paper. It should be an iterative process I would think.

It could be impacted by the head itself, by the temparature, by the humidity,...

- Profiling is about using a calibrated printer to print patches with known RGB values on an unknown paper you are trying to profile. The game is to inject known amounts of inks that would - as a result of the calibration - produced the desired color on the reference paper, and to measure the colors produced. The gap of RGB values between the reference paper and the paper to be profiled is what is captured in the profile.

I am not sure to understand the relevance of the CMYK model in this story, since I assume that the patches to be printed both for calibration and profiling are defined in RGB terms, I suspect that the spectrometer measures the patches in RGB values as well, and the inks used are not CMYK anyway.

Am I wrong somewhere?

Cheers,
Bernard
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opgr
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« Reply #10 on: January 11, 2007, 03:03:57 AM »
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Calibration usually means adjusting a device to a known state. For printing that usually means to linearise the separate primaries. With 12 ink tanks you can argue what primaries means in this case, but for all practical purposes it can be limited to CMYK output.

The calibration target image by HP in the review suggests it calibrates CMYK as well as LCMK. A graywedge gradient would be printed with a transition from LK to K by dithering. The output is  affected by this dithering process...

Adjusting the printing head output to a known state would involve using a designated output paper type, apparently HP gloss.

The actual profiling of the device/paper combo is obviously independent of this calibration state, but IF you calibrate, it should be done BEFORE profiling, which, according to the review is done automatically in that order. When not using HP gloss, I don't know what the target values would be for the calibration process.

Now, the printer prints using a CMYK model with a graybalance and ink deposit based on the paper selected in the OS printer driver. A matte paper will involve less ink and a different graybalance than a glossy paper which will involve more ink.
This however, is usually the most control one can assert on the CMYK output, all other corrections are commonly done in the RGB realm. So you are actually creating an RGB to RGB transform, after which the printer driver and/or the printer do their RGB to CMYK/LCMK magic.


Whether the HP actually does CMYK profiling, I don't know, but the profile target shown in the review looks remarkably like an RGB target to me.
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Oscar Rysdyk
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« Reply #11 on: January 11, 2007, 03:19:54 AM »
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Well, who got out of the wrong side of the bed here? ;-)
Huh? You're losing me, dude. "craquelure"? Why would I expect to see that on a fresh print from an inkjet printer?

Because the ink doesn't hold on the media. Plastic foils come to mind as the obvious example, the plastic coating on the glossy papers is actually pores so the ink can reach the absorbing layer. If the coating is not correctly pores, the ink will not stick to the surface correctly, and either the print head will run right through the previously deposited inkdroplets and cause smearing, or your print must dry really long and end up craquelured.

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And yes, you can adjust the drying time from printing to spectro scanning to whatever you want. 5 mins is the Auto default for busy people. Take a day, a week.

OK, my apologies. I missed that from the review. The drying time remains very relevant for the reason mentioned above, but alsop because some of print colormatching really is a 10degr observer problem for which we don't know what the tolerances are. A proper white balance would be the prime example. Print a grayscale gradient of decent size, let it dry for a day. Then print the same grayscale gradient the next day and immediately compare.

If you don't see a difference, then everything is humpty dumpty, but if you do see a difference then the difference is likely less than 1 delta E... So perhaps HP is correct that the inks dry to within 1 deltaE in 5 minutes, but whether that is enough for the ones purposes remains an individual assesment.

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A linear response is a linear response. 50% in, 50% out. No?

No, 50% of what compared to what?


Quote
It IS profiling the CMYK output. What else would it be?

It may be *calibrating* CMYK, but it doesn't appear to be *profiling* CMYK... The target in the review suggest an RGB profile.
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Oscar Rysdyk
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francofit
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« Reply #12 on: January 11, 2007, 05:49:11 AM »
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So if you calibrate with HP Glossy (or whatever) the calibration will apply to (say) Photo Rag? I'm just trying to get a handle on what the calibration actually does, and how it's different to per-media linearization.
[{POST_SNAPBACK}][/a]
I do not own   this printer, but I like to consult manuals of interesting products:

the Z3100 User Guide reads that calibration(+profiling) should be done for every different paper not yet calibrated on the same set of printheads.
Furthermore there are automatic alerts reminding you whenever you need to perform color calibration and You can check the color calibration status of the currently loaded paper at any time by pressing the View loaded paper key on the front panel...

The manuals are downloadable from this link [a href=\"http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?lang=en&cc=us&taskId=101&prodClassId=-1&contentType=SupportManual&docIndexId=179166&prodTypeId=18972&prodSeriesId=3204970]HP z3100 Manuals[/url]



(Hope  that's not a Manual error like the minimum roll width of 18"  which have been stated and demostrated as a Manual and Spec error: in fact, as per other threads in this forum, the actual minimum for roll width should be the same as that one of sheets, i.e. = 8.3")

Hope this helps
« Last Edit: January 11, 2007, 06:41:19 AM by francofit » Logged

Franco
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« Reply #13 on: January 11, 2007, 06:27:23 AM »
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Can anyone please tell me, if , every printer need rip, or, HP Z3100, no going to neede it, at all.

Thank You

BlasR
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Stephen Best
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« Reply #14 on: January 11, 2007, 07:11:52 AM »
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I do not own   this printer, but I like to consult manuals of interesting products:

the Z3100 User Guide reads that calibration(+profiling) should be done for every different paper not yet calibrated on the same set of printheads.
Furthermore there are automatic alerts reminding you whenever you need to perform color calibration and You can check the color calibration status of the currently loaded paper at any time by pressing the View loaded paper key on the front panel...

The manuals are downloadable from this link HP z3100 Manuals
[a href=\"index.php?act=findpost&pid=95064\"][{POST_SNAPBACK}][/a]

Thanks for the link. So, from page 60 in the Z3100 User's Guide, changing a printhead will flag the calibration for each paper as "obsolete". Given a quoted average life of 2500ml for a printhead, and six printheads in the printer, you're up for a new calibration/profile roughly every 400ml of ink used (3 ink carts worth) ... and for every paper you use. Just as well it's automated! Of course, you could just continue to print with the old profile. There is no printer wide calibration.

Duh! It's 2500ml per printhead, not total throughput. This presumably totaled from just the two colours that feed a printhead. Given that some will get used more than others, and some will fail closer to the minimum warranty value, it's harder to predict when you're up for a new calibration/profile cycle. Maybe someone with a better background in statistics than me can tackle this! Regardless, it's an issue that we'll only hear about after the printers have been out there for a while.
« Last Edit: January 11, 2007, 03:20:59 PM by Stephen Best » Logged
francofit
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« Reply #15 on: January 11, 2007, 09:37:58 AM »
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My guess was that:
..OMISSIS…
... I suspect that the spectrometer measures the patches in RGB values as well, and the inks used are not CMYK anyway.
Am I wrong somewhere?
Cheers,
Bernard
[{POST_SNAPBACK}][/a]
Quote
…OMISSIS…
Whether the HP actually does CMYK profiling, I don't know, but the profile target shown in the review looks remarkably like an RGB target to me.
[a href=\"index.php?act=findpost&pid=95051\"][{POST_SNAPBACK}][/a]

Reading  [a href=\"http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?lang=en&cc=us&taskId=101&prodClassId=-1&contentType=SupportManual&docIndexId=179166&prodTypeId=18972&prodSeriesId=3204970]The HP z3100 User Guide[/url] and based on my understanding, I think that Bernard explanation about calibration/profiling is quite correct.(for space seek, both Bernard's and Opgr's comments are excerpted, so see the complete originals clicking on the arrows on the right of the Quote)

Some specifics topics everybody can read by downloading the the Manuals:

-The profiles generated by the basic sw package (included with the printer) are RGB.

- Optionally  you can buy the additional package “HP Advanced Profiling Solution” which allows you to profile also as CMYK in case of RIP
…The HP Advanced Profiling Solution lets you take control of your colors:
● Calibrate and profile all of your monitors—LCD, CRT, and laptop
● Automated RGB profiling via HP software drivers to ensure accurate printing (photos, designs, etc.)
● Automated CMYK profiling when your printer is driven by a Raster Image Processor (RIP) for
accurate digital prints and proofs
● Easily and visually edit your profiles for ultimate color control….


-The basic sw package (HP color Center) is operationally structured in three phases:
1-Paper Define
2-Calibration
3-Profiling
NOTE You can perform all three operations in sequence as shown, but you can also choose
to start with or stop after any of the three operations. With one exception:
color calibration is performed automatically after adding a new paper type


-and about calibration vs profiling:
 Calibration garantees consistency, while Profiling guarantees accuracy
…Color calibration provides consistent colors, but consistent colors are not necessarily accurate…
… From the measurements made by the spectrophotometer, the printer calculates the necessary
correction factors to apply for consistent color printing on that paper type.
It also calculates the maximum amount of each ink that can be applied to the paper


Hope the above is useful and correct.
Ciao
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Franco
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« Reply #16 on: January 11, 2007, 10:17:30 AM »
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Thanks for the link. ...
...
...it's harder to predict when you're up for a new calibration/profile. Maybe someone with a better background in statistics than me can tackle this! Regardless, it's an issue that we'll only hear about after the printers have been out there for a while.
[{POST_SNAPBACK}][/a]
Stephen,
You are very welcome- glad to be useful once in a while  

About printheads life, for those who have not read Michael's [a href=\"http://www.luminous-landscape.com/reviews/printers/HP-Z3100-review.shtml]review[/url]:
(enphasys's mine): the first one "13 cartridges"(divided may be by a number x? related to Failure Rate of the whole set of 6 heads) could be used as a starting estimated reference for how frequently I should re-calibrate because of printhead change, but only the future experience will tell the truth as both Stephen here above and Michael in his review say.
Quote
excerpt from Luminous Lanscape review of HP Z3100:
Of Print Heads and Calibration
.....The six heads in the Z3100 printer, at $69.95, each cost less than an ink cartridge, have a projected average life expectancy throughput of about 2,500 ML of ink, while being warranted for a minimum of 1000ML of ink. For the sake of argument, since the printers are so new and don't have a public track record yet, let's split the difference and rate the heads conservatively at 1,750 ML. Since each ink cartridge holds 130 ML of inks ($74.95), that means that on average one will have to replace each of the heads after about 13 cartridges of the same ink have been used. In other words, head costs add about $5 to the effective cost of each ink cartridge. This is essentially a trivial amount, and by way of comparison, far, far less than the cost of a single large sheet of fine art paper.

And, to save you the math, with these numbers it will only be after you have used some 156 ink cartridges of all colours before all six heads will have needed to be replaced – the equivalent of more than 4,000 large prints. This is several years worth of printing using a few hundred dollars worth of heads.
....
« Last Edit: January 11, 2007, 10:51:10 AM by francofit » Logged

Franco
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« Reply #17 on: January 11, 2007, 06:45:22 PM »
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Calibration garantees consistency, while Profiling guarantees accuracy
[a href=\"index.php?act=findpost&pid=95102\"][{POST_SNAPBACK}][/a]

Yes, I think this sums it up quite nicely.

Justin.
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Stephen Best
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« Reply #18 on: January 11, 2007, 07:28:14 PM »
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Some further thoughts:

Maybe the printhead replacement and subsequent calibrations aren't that big a deal. For every paper you use, you'll do an initial calibration and build a profile. Then every time you want to do a run with that paper, you do a new calibration. This will correct for any earlier printhead change and also take into account environmentals. The profile you have may not be 100% accurate for soft-proofing but should give close to optimal results on the printer because the calibration is ensuring the best ink loading. Even with minimal (5 minute) dry-down, the relativity of one patch to another should stay about the same.

Looking however at the calibration, it appears pretty simplistic. When you're evaluating ink loading you can look at a number of factors: maximum density, differentiation between the 90% and 95% patches etc but also bleeding (how well fine detail holds up under that loading). There's also per-pass drydown to take account for. The optimal ink loading takes all these into account, but HP's calibration only appears to look at density. This is probably fine for most of their own papers, but people tend to put some oddball media through their printers and it will probably be inadequate here.

Another issue is the number of patches for the profile. At 473 (with the swatches at the top ... I counted them) it doesn't compare to the thrice-read 1728 patch targets I use for my Epson, but will require comparative testing to see how well it performs. HP enables more patches for more money (presumably which largely goes to GM/X-Rite as part of the deal) for those that think it's an issue. Or you could just use your own spectro and profiling software.

Note in the preceding that I haven't seen the printer, nor considering this in the short term (I already have something that works and the paper path of the HP is probably a show stopper for me) ... just ruminating on changes to the printing landscape.
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Haraldo
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« Reply #19 on: January 12, 2007, 07:44:05 PM »
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RE: "craquelure"
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Because the ink doesn't hold on the media. Plastic foils come to mind as the obvious example, the plastic coating on the glossy papers is actually pores so the ink can reach the absorbing layer. If the coating is not correctly pores, the ink will not stick to the surface correctly, and either the print head will run right through the previously deposited inkdroplets and cause smearing, or your print must dry really long and end up craquelured.

I see where you're coming from, but this is not a situation most of us will encounter. I would venture that most here are printing on inkjet-receptor-coated media (or uncoated media but with known ink absorption qualities). I hope I never encounter the dreaded "craquelure" -- except in an 18th century painting!

Quote
No, 50% of what compared to what?

40%M input  = 40%M on paper? Sorry, I'm not a linearization expert, but this has been my assumption in the past. As the HP engineer said, "linear response in colorimetric density as a function of input digital counts." That seems straightforward to me, but someone could probably explain it better. It's certainly not "marketing crap" as your hyperbole would suggest.

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It may be *calibrating* CMYK, but it doesn't appear to be *profiling* CMYK... The target in the review suggest an RGB profile.

I think we're just using different words. The spectro scans the CMYK+++++ target patches to create the RGB profile (in the out-of-box version).

Harald
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Haraldo
aka Harald Johnson
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