Plate / Calibration Curves

[C2C]

Hello,

It has been awhile since i have posted.
So please, be patient
Heres my situation:

Currently we are running Creo's Workshop (v.3.0.3.1) and out put plates on a Trendsetter 800 II Quantum.

We Do not use a calibration curve on all plates output. [ with the exception of some UV jobs, then we apply a AM 5% Cutback to all the plates in that job ]

i have been given the task to create a new *plate* curve with a *15% cutback* for plating of UV jobs.

Up until now on some UV jobs we just selected the 5%-8% AM cutback option in Workshop, but there is no 15% cutback so this is where I assume I need to create a curve which automatically applies this cutback (that is when the plate maker selects the curve prior to plate output) but we normally do not use/apply a calibration curve to our plates (the option is set to : NONE)

I have the Harmony Users Manual in front of me and most of it sounds Greek to me.

So what I have now is:

We setup a Spectrum proofing curve earlier this year

Some Current Curve Data (from off a press sheet)
and I know the target we want to reach *the 15% cutback* but im unsure as of how to go about creating this curve with the data I have. (if its even possible)

Im thinking I need to take the current curve data
and knock it down 15% to create the new "target curve" and then use the current and our newly created target to achieve a new Calibration Curve we can use.

I find this interesting but quite confusing.

Any help would be appreciated.
Till then i will continue to read this manual and see what I can absorb.

Thanks

C2C

Spelling / Additional thoughts / Additional Information

[alarson]

C2C,
Think of Harmony like a thermostat in your house. Your Target curve is the room temperature you would like to watch football in. Your current curve is the actual chilly breeze blowing into the house. The calibration curve is the calculation of how much heat your furnace needs to crank out to get it pleasant.

Plug in the numbers from your Spectrum proof numbers. That's your target. The stake in the ground that all our proofing equipment is aiming towards showing dotgain.

Print out the sheet today and those numbers are your Current curve numbers .

Create calibration curve and voila.

OR, You can crank up the furnace in manual mode. If you want a 15% curve, you can create a 4 color curve as a standalone curve where you punch in a 15% cutback at 50%. The smoothing will make sure there are no jumps in the lookup table which leads to banding.

Hope this helps,
Allan

[marktonk]

Allan,

What a great analogy!!! What game are you watching?:^0

Regards,

Mark Tonkovich
Heidelberg USA
Product Manager, CtP & Proofing

[C2C]

"C2C,
Think of Harmony like a thermostat in your house. Your Target curve is the room temperature you would like to watch football in. Your current curve is the actual chilly breeze blowing into the house. The calibration curve is the calculation of how much heat your furnace needs to crank out to get it pleasant.

Plug in the numbers from your Spectrum proof numbers. That's your target. The stake in the ground that all our proofing equipment is aiming towards showing dotgain.

Print out the sheet today and those numbers are your Current curve numbers .

Create calibration curve and voila."

__________________________________________________ __________________________________________________ ____________________

but a few Qs.

Why would I use the spectrum proof target for a plate curve?
I know the spectrum target curve is supposed to match *or close as possible* what the press outputs.

but I was thinking we need to make a new target (that being a plate with a 15% cutback) and since we dont apply a curve to the plates we make I was unsure where to get the data from to reduce the 15% overall...

So your saying the spectrum target data is usable for a plate curve ?
*what im confused about is when we do a spectrum proof we apply this curve.. but when we make a plate we do not use a curve at all*

I guess im looking at it like, we donot apply a curve to our plates so how do you take 15% away from nothing...
So this is where the Spectrum proof data comes in (since it is supposed to be a close as possible representation) to what the press outputs.
take 15% off that and I should achieve what im seeking?

any clarity on this or am I looking at it wrong/skewed?

Thanks!

C2C

Edited by: C2C on Nov 23, 2007 7:24 PM

Edited by: C2C on Nov 23, 2007 7:30 PM

[gordo]

If you want your UV printing to tonally match yout current non UV presswork that has no curves applied to the plate - then your target curve is generated from the tone values of your current non-UV presswork. Your current curve is the tonal response from your UV presswork that has no curves applied to the plate. Harmony will then calculate a plate curve to bring your UV response to your target non-UV presswork.
This graphic shows the basics of the process using exagerrated values for clarity - if the image doesn't embed in the post then go to the link:

!http://www.bytephoto.com/photopost/data/500/10692Calibration-med.jpg!

http://www.bytephoto.com/photopost/d...ration-med.jpg

The left chart shows your existing Non-UV dot gain curve (cyan). This is your target curve - the tone response that you wish to emulate with your UV printing. The right side graphic shows the tonal response with the same plate setup but using UV ink (could be any other factor that affects dot gain e.g. higher densities or finer halftone screen)
We see that the 50% tone in your target curve actually prints with a value of 75%. What the software does is look at which requested tone value in the current tone response (graph on the right) printed at 75% on the press sheet. In this case the requested value in the file was 25% which printed at the target value of 75%. A calibration curve would then be created that always maps a requested value of 50% to a value of 25%. This is done for other values in the tone scale not just the 50% value.

Of course, if the request is instead to "take 15% out" you would need to know what the requester that actually means by that - i.e. does 50% become 35% or 42.5%? or does it mean that the tonal response on the press sheet should be cut back - in this example it would mean 75% on the press sheet would either become 60% on the pressheet or 63.75%.

hope this helps


best, gordo

[C2C]

"If you want your UV printing to tonally match yout current non UV presswork that has no curves applied to the plate - then your target curve is generated from the tone values of your current non-UV presswork. Your current curve is the tonal response from your UV presswork that has no curves applied to the plate. Harmony will then calculate a plate curve to bring your UV response to your target non-UV presswork."

correct. this i get (sorry if im slow on picking this up)

"We see that the 50% tone in your target curve actually prints with a value of 75%"
Due to dot gain on the press correct?

"i.e. does 50% become 35% or 42.5%?"
Im not following you 100% here. I can see the 35% but where did the 42.5% come from? ( the extra 7.5% )

"Of course, if the request is instead to "take 15% out" you would need to know what the requester that actually means by that - i.e. does 50% become 35% or 42.5%? or does it mean that the tonal response on the press sheet should be cut back - in this example it would mean 75% on the press sheet would either become 60% on the press sheet or 63.75%."

I believe they want want a general 15% reduction across all for UV runs.
Ill certainly ask. I was only left a note on night shifts stating this needed to be done...sometime soon for a test run

So taking my current data (the pdf) and reducing all values listed by 15% (I prefer to start with the 50% dot) would then give me a 15% overall reduction in the plates and therefore harmony would setup a curve (once all info is entered) with values 15% less then the current 'NONE' output that we could then apply to UV runs.

In your example given. our 50% cyan dot is at 75.73 - 15% = 60.73%. but where does the other 3.75% come into play .
Ive read something about a 3% gain in the harmony manual but i do not have the manual in front of me atm

Thanks for the info!
Im on my way to achieving the request and i appreciate the help.

C2C

am I correct in this? (again im trying to catch on here , )

- additional thoughts / questions -

[gordo]

RE: "i.e. does 50% become 35% or 42.5%?"

and "In your example given. our 50% cyan dot is at 75.73 - 15% = 60.73%. but where does the other 3.75% come into play .
Ive read something about a 3% gain in the harmony manual but i do not have the manual in front of me atm"

I gave the two figures because I didn't know what the requester actually means by take 15% out. 50% minus 15% could mean make it 35% (50-15=35) or it could mean 42.5% (50 x .85 = 42.5) depending on your requester's terminology.

RE: "So taking my current data (the pdf) and reducing all values listed by 15% (I prefer to start with the 50% dot) would then give me a 15% overall reduction in the plates and therefore harmony would setup a curve (once all info is entered) with values 15% less then the current 'NONE' output that we could then apply to UV runs."

You can tell Harmony that your target is 15% less than your requested value in your PDF (that's pretending that your PDF values are your current presswork value) however doing so will not result in your UV presswork aligning with your current non-UV work. Typically curves are used to align different print condition (e.g. normalize dot gains) rather than applying an arbitrary value - e.g. take 15% out. If you don't have a well defined, measured, target you could end up chasing your tail with numerous iterations until someone decides that it "looks" good.

gordo

[C2C]

?:|

oi.

You would be surprised at how long we chase our tails :P
Then again, reading over this topic, maybe not.

I really would like to start to understand the task i have been given... and not just push my way through blindly >.<

As far as Im aware, they (the VP) just wants to take what our press outputs on a daily basis
(the pdf #s are the values of what comes off our presses now)
and just reduce it 15% overall for UV runs.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
"doing so will not result in your UV presswork aligning with your current non-UV work."
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I don't think the idea is to match it dead on, i think the VP wants a noticible difference. I believe he wants to see the cutback in order to judge where to go from there (this is usually his style)
Again, without being able to speak with him directly, ( ill do that Monday on Dayshift, been awhile since ive been on days! ) I wouldnt know if hes looking for a 15% cutback in all areas or just in some. ( communication !!! sticky notes do not cut it )

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
"Typically curves are used to align different print condition (e.g.
normalize dot gains) rather than applying an arbitrary value - e.g.
take 15% out. If you don't have a well defined, measured, target you
could end up chasing your tail with numerous iterations until someone
decides that it "looks" good."
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

So I would have to take a UV run press sheet we (and the customer) is happy with and grab the values off that as use those as a target and take my existing current data of what the press out puts now (the pdf)
and punch it all into harmony to make this new plate curve?

If so, what step // what values..... would I be applying the -15% ( to the UV press run sheet data? Since this is what we output now and we want to test a -15% cutback)
and would I apply it overall or individually to each colour? (does it make a difference?)

Thank you for all your help.
Im having a hard time grasping this it seems :X

Edited by: C2C on Nov 25, 2007 1:49 PM

[PeterA]

If you just want to reduce the 50% digital dot ( which when ptd = 75% ) to 60% then you need to take 15% of t 75% which is 11.25%

then the 50% in Harmony tshould be set to 38.75% (50 -11.25)

if you just make the 50% the point in the plate curve it will be smooth.

It will show him what he wants
peter

[C2C]

^ i see .

Using the above example Im going to do the #s ( across all , not just at 50) and post my data.

Ill certainly check back in.

I appreciate all the information and help.

C2C