Agfa Amigo and 20 micron FM screening

[Savage]

We did some FM tests on our current setup. Our workflow currently only has 20 micron FM available. Our Amigo plates technical info says it only goes down to 25 micron. We did a TVI profile for FM, and used the NPscreen profiles from ECI.
The results weren't good. We couldn't match our certified proof, all the images were lacking contrast, and there was an overall random color shift in the images, despite all the densities were controlled and stable.
I was expecting problems in the lighter areas, and possibly some loss of detail all around. I was not expecting color shift and contrast problems.
Could this be caused by the plate not being up to spec with our FM screen, our that would not explain the results.
Can someone help me understand what went wrong? Thank you.

 

[VladCanada]

<<Resolution 1-99% with :Sublima 240, 200 lpi. 25μ FM>>

Your Tech was right; do not expect a miracle from plates working out of spec.
That minimum of 25μ dot size - because of thermofuse technology.

 

[gordo]

<<Resolution 1-99% with :Sublima 240, 200 lpi. 25μ FM>>

Your Tech was right; do not expect a miracle from plate working out of spec.
That minimum of 25μ dot size - besause of thermofuse technology.

Just to expand a bit on the issue.

Typically a 20 micron FM screen will use 20 micron dots (4 10.6 micron pixels) up until about the 30% tone. At about 30% the dot size begins to grow to 25 microns. So, from 1%-30% and 70%-99% the size of the dots that make up the screen are out of spec for your plate. Those tones will be unstable and inconsistently rendered on plate and hence will not be reliable on press. That can cause color shifts.

An inability to match an existing proof that is based on an AM/XM screen is a separate issue. The small dots and their distribution means that, for the same tone value on press, and FM screen will exhibit a higher chroma. Hence for the same tone value on press the color will be different.

Contrast problems can be caused by incorrect tone reproduction curves being applied to the plates or it can be caused by poor ink transfer, or poor ink performance with the microdots that make up an FM screen.

If your workflow currently only has 20 micron FM available, I would suggest that you speak to your vendor. It is likely that other (larger) screen dot sizes are available. Perhaps you can persuade them to give you a (free) trial license for a coarser screen in order to evaluate its suitability for your shop.

hope that helps, gordon p

 

[Savage]

Thank you both for your answers.
@gordo: I think you gave a very good explanation on what may have caused both the color shifts and the lack of contrast. Just for the record, i knew we could't match an FM screen with an AM/XM screen, thats why we did our tests against a certified proof calibrated to fogra43, so if nothing went wrong, it should have matched.
As for your suggestion, i will try it. If if fails i will talk to a plate vendor to get a couple of boxes of some plate that can do 20 microns. It will be a bigger pain to setup, but i'm willing to give it a go.
Again, thank you very much.

 

[gordo]

[SNIP]Just for the record, i knew we could't match an FM screen with an AM/XM screen, thats why we did our tests against a certified proof calibrated to fogra43, so if nothing went wrong, it should have matched.[SNIP]

It is unfortunate that, AFAIK, Fogra characterization data is based on linear film (!) - although, as is typical with ISO/Fogra documentation, they are not really clear on this basic issue. You might suppose that with CtP you should run linear - despite the fact that linear film does not deliver linear plates. But that's another discussion.

Because of this 1970s mentality of linear film as the standard, Fogra 43 as your target for color will probably mean that your presswork will run very dark due to the higher dot gains compared to your Fogra 39. Does your current proofing show this? i.e. Fogra 39 (I assume) proof vs Fogra 43 proof.

BTW, I haven't been able to find the Fogra 39 and 43 profiles ( I would sure appreciate it if someone sent me their copies at pritchardgordon @ gmail (dot) com )

best, gordon p

 

[maas]

We are about to undertake a similar test, on newsprint using a Goss HT70 press.

We have Agfa Polaris platelines and Harlequin 8 rips, currently we produce 10000 plates per week at 200 per hour, our Agfa representative tried to push the Sublima xm sceening solutions stating the FM screening at 25 uM ( 1880 dpi) would reduce the 200 plates per hour to 80, i have read several reports which claim little or no loss of Ripping or imaging speed, any feedback would be appreciated

regards
Maas

 

[SteveAgfa]

maas:

What lpi and resolution are you imaging at now?

 

[gordo]

our Agfa representative tried to push the Sublima xm sceening solutions

What lpi screening are you using now? What lpi XM screening is your representative suggesting? Why are you thinking of changing screening?

best, gordon p

 

[maas]

Gents I stand corrected, we were running 200 plates per hour at 100lpi/1016 DPI, we changed to 110LPI/1270DPI and run 185 plates per hour.

The project is currently at its infancy and first and foremost we want our vendors to be on board, my initial opraoch to Agfa was along the lines of " we wish to test the potential of FM screening , is this feasable on our current Agfa equipment and plates" the response was somewhat vague and heavily geared towards an FM/AM solution (Sublima) to compensate for the issue ocasianaly seen in flat tints in FMscreening. ( but then conventional screening also has issues in midones)

Our focus is to test FM screening, and therefore we would not consider a AM/FM solution at this stage


The reason which we want to test FM screening is due to the very real benifits in terms of quality reproduction, ink saving etc

regards
Maas

 

[gordo]

@Maas For newspaper work, the most used FM dot size is 35 micron. On a 1016 DPI device that's a highlight dot size of about 30 microns (~2% dot at 110 lpi) and a ~43 micron midtone dot. I believe that with your Harlequin RIP that's the HDS Coarse screen (check your documentation). That appears to be within your output device's specification. Agfa should be able to confirm whether that is within specification and tell you whether they will support it or not.

best, gordon p

 

[SteveAgfa]

maas:

I'll speak in generalities, as I do not wish to undermine the process of those closer to the situation.

Sublima Screening was initially developed for the newspaper market. It's not a "stochastic" solution or a hybrid of stochastic and AM, but rather a higher-line ABS (AM) ruling, with the highlights and shadows converting to a frequency (not stochastic) implementation - [read - we'll take out dots along the established AM axis]. This is because for the targeted application, at higher line rulings, we don't deliver a dot that's too small to hold on press.

This higher AM screening in the midtones delivers smoother flat tints (think bar graphs and weather maps) and the higher LPI also delivers greater image detail than conventional AM rulings from 1 - 99% (think ads).

As Gordon mentions, the typical FM screen for newspapers is 35 microns - growing to 43 microns in the mid-tones. Especially for flat tints, this can start to look grainy.

The XM approach of Sublima delivers positive attributes of both technologies - smoother flat tints of AM, and consistent highlight and shadow values of FM.

If you have the opportunity to try both the XM and FM approaches, do so, and find the best fit.

WRT speed differential, the higher the resolution of a capstan drive device such as this, the slower the throughput. It's not a ripping issue. In the thermal world, lower resolutions such as 1200 are interpolated, as a lower resolution requires higher power, and thermal devices tend to be maxed-out and optimized around 2400 dpi. That's why you may have read that there is no difference in throughput speed between 1200 and 2400 dpi, it's because the engine workflow is turning 1200 data into 2400 dots.

With that, I'll let our colleagues down under address your specific concerns.

Regards,

 

[gordo]

@Maas - As always, try and compare apples to apples. Compare :Sublima (or other XM type screening) to your current AM screening at the same lpi rather than comparing them at different lpis. That will help you see what value the XM solution brings you. If you can use a standard AM screen to achieve a higher lpi - that is usually the best way to go. If you want to try FM then, as I wrote, the standard for newspaper is about 35 micron. Due to the absorbency of newsprint, it's unlikely that you'll see any midtone graininess resulting from the large midtone dots.

In any case, involve your suppliers in the test, so that they can help guide you and make sure you stay within specification as well as what they are willing to support if you decide to switch.

If you can't do a dedicated press run for your testing then what some papers do is create an advertisement for some aspect of the newspaper (e.g. promote the classified section, or promote fashion coverage) and hide subjective and objective test elements within the ad.

good luck, gordon p

 

[maas]

gents

Thank you both for your input, Steve we have a great relationship with Agfa and are committed to trailing the Sublima product after we have tried pure FM first, we will involve all vendors ( ink, fount etc) in this process as well as a team of staff with a can do attitude.

Gordo i am sure you have heard this many times but this trade is indebted to you for your unselfishly sharing your experience and knowledge.

If i may i would like to keep you both in the loop

regards
Maas