Hybrid raster

[Ricky]

we are now trying to using a hybrid raster to print out magazine. It looks great. But the problem is in the color, it looks a little bit darker, but the details of the picture all came out great, smooth. Usually we using raster 150 or 175, the color came out okay. But we trying to take it to another level.

we using Heidelberg Suprasetter 105, Heidelberg SM 102 - 8 color, hostmann Resista Ink.. we try to print it on Matt paper.

So what should i do to make it nearly perfect?

thank you...

 

[gordo]

we are now trying to using a hybrid raster to print out magazine. It looks great. But the problem is in the color, it looks a little bit darker, but the details of the picture all came out great, smooth. Usually we using raster 150 or 175, the color came out okay. But we trying to take it to another level.

we using Heidelberg Suprasetter 105, Heidelberg SM 102 - 8 color, hostmann Resista Ink.. we try to print it on Matt paper.

So what should i do to make it nearly perfect?

A hybrid raster and a regular AM screen are exactly the same - except for the size of the 1% and maybe 2% dots. Therefore it won't look any better, or smoother, or more detailed than a regular 150 or 175 raster.

If you want to "take it to another level" then forget AM/XM/hybrid AM and go to FM/stochastic.

best, gordo

 

[Ricky]

Yes I know about the Stochastic, but before we up to that level, we would like to trying and conquer the Hybrid first. Which at the moment, we are unsatisfied wit the result.

So let say I would like to try to go Stochastic. What kind of things should I prepare it well. The adjusting color on the pre-press? Not running the press machine at its top notch? any advices?

 

[gordo]

Yes I know about the Stochastic, but before we up to that level, we would like to trying and conquer the Hybrid first. Which at the moment, we are unsatisfied wit the result.

Why are you doing Hybrid? Why not use regular AM since it is the same thing (except for the size of the 1% dots).

I assume that you are trying to print with a finer (higher lpi/lpc) screen. If so, you need two things:
1: Consistent and reliable printing with your current screening.
2: Proper dot gain compensation curves applied to the plates to make the higher lpi screen print the same final tones on press that your current screening does.

If you don't have #1 then you can't do #2.

If you can do #1 then you can do #2 and there is no need for prepress to make any adjustments in color.

best, gordo

 

[chevalier]

If do don't already have one implementing a robust maintenance schedule and log for both your prepress and press equipment is a must if you want to move to finer detail. Depending on how detailed you want to get you can't half-ass or bottom barrel it when it comes the blankets/plates/inks/chemicals and paper you are using either. It is astounding what can be achieved when you have a honed process with a controlled and maintained environment.

As gordo mentioned recalibrating curves is really a must for each LPI or dot size.

 

[Ricky]

Thanks a lot for both of you. it really helps me to understand it clearly now.. Now i see the problem is, we havent recalibrating the curves again.

Should I recalibrating once a month or depending on the numerators (said every 500.000 or 1.000.000) ?

Mostly we operate 24-7....

 

[chevalier]

Normal practice in my experience is to calibrate once a year unless you have some kind of major maintenance done to a press (all rollers replaced, etc.). Calibrating each linescreen/screening system is laborious and expensive. I haven't seen a plant yet that can justify doing this more than once a year but i'm sure there is somebody out there doing this biannually or quarterly.

If you are a G7 qualified printer you are only required to re-qualify once a year. The re-qualification consists of the same steps as a calibration only with a cleary defined process and third-party calling the shots. If you are going to go through this process and aren't already G7 I would recommend at least looking into it. If you are in the Eastern US and looking at joining the G7 bandwagon I highly recommend Larey Kauffman or Darrin Raposa with Fujifilm.

 

[gordo]

Thanks a lot for both of you. it really helps me to understand it clearly now.. Now i see the problem is, we havent recalibrating the curves again.

Should I recalibrating once a month or depending on the numerators (said every 500.000 or 1.000.000) ?

Mostly we operate 24-7....

Calibration means putting the system in a known condition.

Once the CtP is set up by the vendor's engineers then the CtP calibrated.

Plates containing tone patches are run on press at standard solid ink densities (however those were arrived at).

Then the tone patches are measured and compared with the desired tone response (an ISO curve, previous printing, etc.)

Based on that info a curve is created that will be applied to the plate that will generate the desired tone response on press.

From that point on - plates need to be checked to ensure that the tone values that the curve(s) are creating remain consistent. This is to ensure that plate imaging is consistent. Plates can be checked daily or weekly or monthly. There will be some natural variation in the tone values on the plate. Chart the tone values in a spreadsheet. Allow for the natural variation - perhaps +/2% at 50% (i.e. 48%-52% is acceptable variation at 50% tone on the plate). Tracking plate imaging will tell you if the imaging system is drifting or if there is a problem. Usually, if there is a problem in plate imaging it may require the CtP vendor to come to the shop to recalibrate the unit or determine why the image on plate has changed.

Normally you do not change your plate curves unless you want a different tone response on press, or if you are running a different paper, or if you change plate type. You should avoid trying to fix plate imaging problems or press problems with curves.

best, gordo

 

[chevalier]

Glad to see you picked up what I left out! Every plate we image has a CtP plate control strip way down in the gripper. It identifies the time, angle, screening, dot-type, color separation, curve, workflow, and other settings used to generate the plate. It also has a strip of calibrated and uncalibrated test blocks that be read with our platescope. We spot check instead of checking every plate to verify compliance. I have implemented these strips everywhere I have worked even if we didn't have a platescope or other plate reading device. That way when we did come across something and a vendor was brought in any plate could be checked. It makes it very easy to identify or eliminate this variable when troubleshooting.