Re: Epson 4900 Calibration
Re: Epson 4900 Calibration
- Subject: Re: Epson 4900 Calibration
- From: Terence Wyse <email@hidden>
- Date: Wed, 06 Apr 2011 14:18:52 -0400
EFI's "calibration" is strictly a colorimetric linearization....no overprints are used AFAIK for the re-calibration (the quality control target is used as a reference but that's all).
The confusion is that during the initial base linearization, overprints are used to set total ink limit and in some of the other steps during the *initial* base linearization. The per-channel ink limits use L*a*b* (limits are set based on chroma primarily) and the L*a*b* values set during the initial base lin are used later for a re-lin. But an EFI re-linearization/calibration is fundamentally different than GMG...GMG uses about a 500 patch target for re-cal that includes overprints and will adjust the overprint combinations as well as the pure ink ramps....GMG essentially uses a "mini profile" for calibration.....and to be precise, GMG only considers the C+M+Y overprints....K is treated using L* only.
Because EFI uses more-or-less a re-linearization process, re-profiling is almost always required to truly bring the system back into complete calibration....with GMG that is not the case.
Terry
On Apr 6, 2011, at 1:36 PM, Mike Strickler wrote:
> That wasn't the vendor speaking, Scott. The last step of the base lin procedure involves printing and measuring the "Quality Control" chart, which does have many overprint patches, like a mini profiling chart. Exactly how that data is used I cannot say because they don't share this information, but there it is. I doubt it's merely a check/confirmation, because in the hundreds (thousands?) of base lins I've made I've not received any negative feedback after this step, e.g., "Failure--do it again," so I assume there is some slight tweaking of data at this stage.
>
> Also, remember that at the beginning of the base lin procedure you must specify the printer, resolution, screening, etc. This is because there is a database of baselins EFI has made with these combinations, and this provides a starting point for the ink limits and linearizations. These linearizations have also been tested with respect to overprint behavior and gray balance (which of course involves CMY overprints). This is why you are given acceptable ranges for per channel ink limits--do you think these limits are arbitrary? No, they came from actual testing of the results. It would be pretty silly to include an extra step that adds several minutes to the process just to mystify and mislead customers.
>
> Let's dial back the rhetoric. I was asked for my own description of the process, and this I've done. Some of this comes from EFI's engineers. If you want to read EFI's ad copy it is all available on their website. They say nothing about the underlying math in their base lin procedure, by the way. This is typical of EFI's marketing, which tends to emphasize convenience and productivity over the sort of arcane technical details we consultants find interesting. And for customers, the baselin is something they'll probably never encounter, as they will usually be provided with complete print environments for their printer and media.
>
> Please contact me if you'd like a demo copy of XF so you can see its features firsthand, compare it with GMG, et al. I can follow up with you, give assistance, etc.
>
> Mike
>
>
> On Apr 6, 2011, at 8:55 AM, Scott Martin wrote:
>
>>
>> On Apr 5, 2011, at 8:04 PM, Mike Strickler wrote:
>>
>>> No, it isn't based on density. The algorithms are proprietary and are based on spectral measurements from each model of printer and its ink set. Gray balance, gamut, lightness, overprints, smoothness of gradations, light-dark ink distribution--all these factors are taken into account.
>>
>> They consider the overprints for the initial base linearization? Right. Sounds like the typical BS often heard from vendor. "We use proprietary Artificial Intelligence! Its Secret Sauce we can't talk about. Its much more advanced than the Status T density linearization that other, more basic RIPs use."
>>
>> If we're going to have a conversation about different calibration procedures then let's do that, complete with the details. Give us some credibility for intellegence. Most of us on the list can easily dive into specifics and appreciate a more sophisticated approach when we see one.
>>
>> (I'm speaking to this imaginary vendor - not you Mike!)
>>
>> Scott Martin
>> www.on-sight.com
>>
>>
>
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