Further to Kamil und Peter excellent komments,
The only “sensible” solution, in my opinion, whenever TAC is deemed so important, is to defer its judgement as further down the line as possible, in terms of workflow. In other words, use a full RGB workflow at the client side and let the printer, who knows
most about print conditions, decide. Let him carry the responsibility should something “go wrong”.
Most printers don’t have the time or the resource to do any kind of testing, not the ones that I know and worked with or for over the past. No wonder they are so conservative! At the very least, in my opinion, a printer should be able to honor “bare-minimum”
kind of industry practices, like Adobe Photoshop 260% Uncoated, 260% is a age-old figure associated with Uncoated paper in the industry. It traces its day to Advertising Rates & Data. To me, it is universally agreed-upon “standard” (target). If a printer
finds himself unable to meet 260% TAC on Uncoated paper, perhaps it is time to consider changing printer or having a serious conversation with the printer technical representative, which is usually the prepress manager who does not have a clue as to what is
going on with color reproduction… (I’m not trying to be sarcastic, just “realistic”)
Know that I personally consider 260% to be “conservative” in terms of TAC and, given the knowledge of some presses, and some past work I seen printed on Uncoated paper, like some Cirque du Soleil lavish, 4 color process brochures, 270% -- 280% and even 290%,
it is not far-fetch. Anything is possible when you have the customer sitting by the press side and willing to pay for additional press time and material.
As a prepress policy, I would not do all Uncoated jobs at 280% but for those that are warranted, why not? The customer is not going to be disappointed. I suspect many shops have slowly increased their TAC over time. At least, the “better” printers I know have.
It’s not that hard to determine but it takes the time of one person, like Peter, to do it!
TAC for Coated paper ought to be 320%, at least. Depends on the nature of the ink coverage over all.
It should be dictated by the images, whether they are heavy and what is the surface represented by those “dark areas”?
At one extreme, you could get away with 400% TAC in small areas but never over large areas, that’s asking for trouble.
Higher TAC remains useful to push contrast in images but here are some last comments…
A) It comes down to prepress policy. I have worked in environments where they privilege “automation” over “customization” or “optimization”, meaning, they don’t stop the line to look at individual images. PDFs come in through the FTP pipeline and away to plates
they go. The least people touch the job on the way to the press, the happier management is. So all arrangements, if any, have to be made ahead of time with customers, that’s the only alternative.
B) If discussions are made ahead of production, a certain kind of planning becomes possible and TAC *can* be discussed between the client and the printer.
C) Most printers I know here are not that knowledgeable, technically. It seems to me that “technical printing knowledge” is slowly disappearing from the face of the earth, on both sides of the print equation, on the client side and on the printer side.
D) It takes time to build quality. At the rate everything is going today, quality becomes second to quantity, the idea is to produce an ever larger number of widgets at decreasing costs. Economics is the driving factor.
My VERY humble set of experiences.
Hi Dwight, in accordance with Peter (and by my long term experinece) - I do not use algorithms (even if the RIP contains it). Much better is have printed a good TAC target, make some measurement with a good handheld, and a carefully examine the material and
overprint patches.
Cheers, Kamil,
Dwight,
For ink limit, we work with values from experience. It depends on various variables like the used ink, the substrate, the resolution, the printing speed, usage of light inks, ...
We have not yet found an algorithm that calculates it based on the linearized single channels. Hence we use a TAC chart when we have a new combination of parameters. As printed ares above the maximum ink threshold may have "artefacts" that cannot get caught
using a spectrophotopmeter, a user has to decide what limit to set. Important: it shall define the maximum TAC that can get printed on that substrate. A further reduction to less TAC should be done when generating the ICC profile.
Happy to hear about other experiences.
best
Peter
> On 22.10.2018, at 13:31, Dwight Kelly <
dkelly@apago.com> wrote:
>
> Hello,
>
> I’m looking for references on device linearization techniques and algorithms.
>
> Have an inkjet textile printer that’s proving difficult to characterize because of the amount of ink it lays down. Don’t want to just pick an arbitrary ink limit. Would rather calculate it empirically.
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