Kodak Gen News
- Thread starter Shediac
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KevinC@EFI
Well-known member
Shediac - because we use a 5000dpi SQUAREspot imaging head to achieve 1200dpi output resolution, we draw those dots EXTREMELY precisely. This allows us to support up to 200lpi hybrid AM screening at 1200dpi, or 36 micron FM screening.
Of course, this is also dependent on the plate you choose, but 133lpi is no problem on most thermal newspaper plates.
Kevin.
gordo
Well-known member
I have to disagree with Kevin on this one.
Shediac is likely concerned about achieving all the grey levels needed for 133 lpi screening on a 1200 dpi device.
The classic formula to determine grey levels is:
(dpi/lpi) squared + 1 = number of grey levels
So for 133 lpi at 1200 dpi:
1200 dpi/133 = 9
9 squared = 81
91 + 1 = only 82 possible tones
However, since about 1985, Supercell screening (a function of the RIP not the output device resolution) has eliminated the grey levels limitation by "dithering" the halftone dots. This type of conventional AM screening is available, if not the standard, from all the vendors - including Kodak.
Here are some of the popular brand names:
Agfa - ABS - Agfa Balanced Screening
Heidelberg - HDS - High Definition Screening, and later IS screening
Harlequin - HPS - Harlequin Precision Screening
Creo/Kodak - Creosettes/Maxtone
Fuji - just since 2004 CoRes screening
More info is available here:
Quality In Print: Halftones and grey levels - part 1 of 2
and here:
Quality In Print: Halftones and grey levels - part 2 of 2
best, gordon p
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KevinC@EFI
Well-known member
To get technical, 9 squared is 81.
The point being, we support 200lpi on the device he mentions, so his need for 133 is certainly met. My point about SQUAREspot enabling 200lpi in a robust, consistent manner on a 1200dpi device stands.
Kevin.
KevinC@EFI
Well-known member
Actually, as Gordon rightly points out, we support normal 200lpi screening on our 1200dpi engine too (using supercell dithering, as he describes). Normally though, for something as high as 200lpi on a cold-set newspaper press and low-grade stock, we would suggest a hybrid screen to improve printability and quality.
Hybrid screens differ in the highlights and shadows from a normal screen. Essentially, at a certain minimum dot size, instead of making the dots smaller we start removing them in an FM-type manner. This gives fewer dots instead of smaller dots - allowing a finer screen overall (especially relevant in mid-tones) while ensuring you can actually print/hold the highlights and shadows.
If you want more detail on hybrid screens, I can send you some. Most vendors offer such an option these days.
EDIT for clarity - you shouldn't need to purchase anything special in addition to the normal screening to print your 133lpi work.
Kevin.
gordo
Well-known member
To get technical, 9 squared is 81.
The point being, we support 200lpi on the device he mentions, so his need for 133 is certainly met. My point about SQUAREspot enabling 200lpi in a robust, consistent manner on a 1200dpi device stands.
Kevin.
Thanks Kevin for catching my typo (but I already caught after I posted and had edited accordingly).
Yes you support 200 lpi, now he knows how it's done in the screening engine. I did not speak to SQUAREspot because it did not seem to be relevant to the OP's question.
best, gordon p
gordo
Well-known member
To do 133 lpi using a conventional AM screen from Kodak, since it's supercell screening, as Kevin says: "you shouldn't need to purchase anything special in addition to the normal screening to print your 133lpi work." You'll get all
If you want to use a Hybrid AM screen (what Agfa calls XM screening) then I believe you may have to pay for that capability. As Kevin said "Most vendors offer such an option these days." I take "option" to mean something not standard and hence you will need to pay for it. Kevin would know better than me about Kodak pricing.
There are two screening concepts here.
1) Supercell AM screening is used to achieve all the grey levels in the halftone screen when the grey level formula says that you don't have enough dpi in you output device.
2) A hybrid AM screen is used for a slightly different purpose. It is used to recover tones that would otherwise be lost because of imaging device/systems limitations. For example, say your CTP/plate combination could not hold a 1% or 2% halftone dot. Those dots would either not appear on the plate at all or would not hold on press. The result would be a loss of those dots and the tones they represent. This is very common in, for example flexo printing because of the low resolution of the rubber-like plates.
Hybrid AM screens get around that problem by using the smallest dot that can be held by the imaging system - e.g. 4% dots - and simply make lighter tones by removing a number of 4% dots from the screen. The fewer the number of 4% dots that are used - the lighter the tone appears. The result is that you recover the tones that would have been lost due to the imaging limitations (CtP, plate, press) of the imaging system.
More detail with illustrations here: http://qualityinprint.blogspot.com/2009/03/hybrid-am-screeningxm-screening.html
best, gordon p
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J
Well-known member
Could you elaborate? Are you saying that other vendors can't deliver 200 lpi on a 1200 dpi device? What do you mean by "robust"? Do you mean that other vendors can't deliver 200 lpi (or 133 lpi) consistently on their plates?
j
KevinC@EFI
Well-known member
Based on all the information I have and can find for like devices, and the answer is no, our competitors can't deliver 200lpi at 1200dpi.
Steve, correct me if I'm wrong, but for example the data sheet on the Polaris says 3-97% @ 150lpi maximum (for ABS screening), or 180lpi if you go to hybrid screening. The Gen News supports 200lpi @1200dpi with our equivalent to ABS screening. Hybrid would allow you do do more, but I'm not sure offhand what that would be (I'd be surprised if a coldset newspaper press could hold more).
The big difference is our 5000dpi thermal SQUAREspot head can draw the dots much "cleaner", reducing sensitivity to all the variables in the production process, and delivering something much more consistent. Other newspaper devices (mainly violet) use Gausian laser systems, with a laser dot size of 800-1000dpi (larger than the 1200dpi pixels they're exposing), limiting their ability to draw small dots sharply (i.e. only 3-97% at 150lpi as above), and increasing their sensitivity to production variables.
The "soft" edge of the exposed dot - the parially-exposed transition zone between the fully exposed dot and the unexposed background - is what's sensitive to variation in exposure, processing, plate sensitivity, environment (heat/humidity), plate age, phases of the moon... etc.
The more sharply defined that transition area is, the less sensitivity to variation the system has. The smaller the dot you're trying to make, the greater the proportion of "sensitive edge area", and the greater the impact of those variables. At 133lpi, the difference is smaller (but still measurable and significant). At 200lpi (@1200dpi), it would be the difference between something that works in a production environment, and something that you'd have to babysit plate-by-plate to get anything useful at all.
We do the same in commercial CTP at 2400dpi - using a 10,000 dpi laser spot to draw very clean dots with very little "sensitive edge area".
I have some data and charts to illustrate that effect if you like. Let me know.
Kevin.
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