A few recent threads have gotten me thinking...
- Thread starter Slammer
- Start date
I would say this isn't necessarily true. We have used processless plates that we can't accurately measure for the last 7 years. I only have a vague idea of where I'm starting from but I am reading the end result, the press sheet, and creating and adjusting tone curves from that info. It is irrelevant what the CTP machine outputs, linear or not linear, only thing you're selling is printed materials, so all that matters is that the end result is within spec to whatever standard you're aiming for. We're achieving that with one curve. If it drifts we tweak it. If we have reports from press side saying runs are within standard target's tolerances, then why does it matter where we started from? Our CTP plates have never varied enough to warrant needing a linearization curve to monitor it. Have you found your CTP varies enough it would throw your final print result out of tolerance?
Just thoughts...
buckeye
Well-known member
I hear what you're saying Prepper but our shop's pressroom has a bad habit of assuming it's the plate first and foremost when something isn't matching to our certified proof. I at least like to know what I'm giving the pressroom, dot percentage wise that is. Our processor plates where profiled/footprinted with a linear plate and our processless plate without. I like the idea of only one curve but I still like to know what's on the plate.
buckeye
Well-known member
Slammer, I hate to assume anything, but if you know for sure your CTP is linear without a curve I would be inclined to agree that the processless plate would also be. My CTP device isn't. I'm surprised yours is. I was always told that it's just inherent of these devices. We've had two different devices and both were producing a 44-45% dot in the 50% on the scale. Like Joe said, consider yourself lucky.
dabob
Well-known member
I was just over on google and searched for processless plate measuring and it spit out a bunch of links . . . we still are using violet so I have no experience in this area . . .
https://www.google.com/#q=processless+plate+measuring
https://www.google.com/#q=processless+plate+measuring
Slammer
Well-known member
Aaaactually we are the plate reps and when I ask the manufacturer the same question I get their standard statement of....: "Umm!" Which also answers Arossettie´s qestion.
Amen to that.
I would tend to disagree with you on this, at the moment our company supplies the Kodak brand of CTP but before that I worked as one of the roving Esko techies and I have never had many issues with plate output that was not inherently linear. Having said that I hear from reliable sources that some cheap as chips Chinese CTP units, or CTP´s that use lasers made in China can often have problems keeping a constant laser output resulting in varying isodensity readings of the dot; more of a annoying issue on offset but deadly on Flexo by the way.
I got the googles too, from your links however I did see that the Techkon boasts processless plate measuring capabilities, gonna give them a call and see what they say.
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buckeye
Well-known member
Slammer, just so happens that one of our plate reps was in yesterday and I bounced the linear curve question off on him and he said he's never seen a D.O.P (Develop On Press) plate that output linear without a curve. Said that the closest he's seen is like a 52% in the 50% patch and that was with a Kodak CTP device. We've had two different Screen devices, one violet and one thermal and, like I said before, both were 6% light in the 50% patch - on the standard plate. On another note, we had a fellow in to test out the Heidelberg/Agfa D.O.P plate and he had a Techkon plate reader that seemed to work fine.
Red_Right_Arm
Well-known member
I haven't read through all of your replies here. So forgive me if someone has already covered this answer. But I think that you can get away without using a plate curve so long as you are able to verify that the plates are always being produced consistently.
For example, if you set up a 50% block. Then image it on your laser. Then expose it. Then wash it. Then finish the plate processing. Chances are that 50% dot might really be, whatever, 48% when measured on a device such as a Betaflex. Okay, so now you know 50% used in your file will produce 48%, or whatever, on your plate. Using this measuring, you find out what percentage is produced for all of your control blocks: 100%, 75%, 50%, 25%, 10%, 5%, 1%... or whatever you deem to be needed. Let's say that you find out that these blocks actually come out as 100%, 77%, 48%, 28%, 12%, and 2%.
Now that you know this, all you'd have to do is make sure that each time you make a plate these are the values that you consistently get. You can achieve this by creating a small 1-BIT TIFF of these values, and being sure to add this small scale to every plate you make. You cut this scale off and measure these values, and as long as they keep giving you consistent values, your system is still stable.
Now, if your system is stable in this fashion, you can be sure that your curves are accurate. In that, the 50% block was plated at 48%. It will always be plated as 48%. And with that 48% your press has a dot gain value of 68%, or whatever. You can tell your RIP "I expected 50% but I got 68%. So do your thing and pull this value back." So long as you keep plating consistently, the adjustment that the RIP makes should get you where you need to be with only one curve.
BUT (there's always a but), this whole set up only works IF you actually can plate the values consistently. If the laser, or washout brush, or plate material fluctuates, then the only way to fix that with one curve is to find out your new plated values, and refigure all of your curves based on that. It isn't the best set up, but it can work so long as you can guarantee your system is reliable.
For example, if you set up a 50% block. Then image it on your laser. Then expose it. Then wash it. Then finish the plate processing. Chances are that 50% dot might really be, whatever, 48% when measured on a device such as a Betaflex. Okay, so now you know 50% used in your file will produce 48%, or whatever, on your plate. Using this measuring, you find out what percentage is produced for all of your control blocks: 100%, 75%, 50%, 25%, 10%, 5%, 1%... or whatever you deem to be needed. Let's say that you find out that these blocks actually come out as 100%, 77%, 48%, 28%, 12%, and 2%.
Now that you know this, all you'd have to do is make sure that each time you make a plate these are the values that you consistently get. You can achieve this by creating a small 1-BIT TIFF of these values, and being sure to add this small scale to every plate you make. You cut this scale off and measure these values, and as long as they keep giving you consistent values, your system is still stable.
Now, if your system is stable in this fashion, you can be sure that your curves are accurate. In that, the 50% block was plated at 48%. It will always be plated as 48%. And with that 48% your press has a dot gain value of 68%, or whatever. You can tell your RIP "I expected 50% but I got 68%. So do your thing and pull this value back." So long as you keep plating consistently, the adjustment that the RIP makes should get you where you need to be with only one curve.
BUT (there's always a but), this whole set up only works IF you actually can plate the values consistently. If the laser, or washout brush, or plate material fluctuates, then the only way to fix that with one curve is to find out your new plated values, and refigure all of your curves based on that. It isn't the best set up, but it can work so long as you can guarantee your system is reliable.
gordo
Well-known member
At: Red_Right_Arm I think the problem raised in the thread was the inability to measure the plates and hence to verify that they are being imaged consistently.
Slammer
Well-known member
In the meantime I have measured a handful or two of (Xingraphics) plates coming out of our trendsetter but also plates from our customers and they all seem to be linear, ok +- 2-3% that I am willing to write off as inconsistency issues with my trusty old D19C, In a few days I´ll be getting my hands on a Köth Chameleon and plan on taking it for a test drive.
Maybe a bit off-topic but does anyone know how to unlock new functions on a Gretag Macbeth D19C densitometer? What's the password? On my D19C the plate reading function is unavailable - locked and it would really come in handy.
Here is a great choice: Choice® 900
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