Ellipse vs Euclidean

[Luvdgoof]

I work for a package printing company that prints a large variety of graphics on mostly SBS Paper. Graphics can be simple text and flood colors for cosmetics, packages with images of the food up to more upscale beauty products with a lot of detailed flesh tones and faces. We are currently running Paragon Ellipse35 dots at 169 LPI. We have 3 KBA Offset presses that have their own dot gain curve setup to GRACoL for each press. It was recently recommendation that I should be using Euclidean dots, as it is more standard in my industry. We are using Ellipse35 because that is what has always been used here and no one really asked why, until now. I have two main questions about this.

1) Do I stand to gain quality and reduce problems on press by switching to Euclidean?
2) What would be the best way to do testing between the two?
3) Should plates be output without any dot gain curve to compare the two more accurately, or would using the current curve for both work just as well?

 

[gordo]

I work for a package printing company that prints a large variety of graphics on mostly SBS Paper. Graphics can be simple text and flood colors for cosmetics, packages with images of the food up to more upscale beauty products with a lot of detailed flesh tones and faces. We are currently running Paragon Ellipse35 dots at 169 LPI. We have 3 KBA Offset presses that have their own dot gain curve setup to GRACoL for each press. It was recently recommendation that I should be using Euclidean dots, as it is more standard in my industry. We are using Ellipse35 because that is what has always been used here and no one really asked why, until now. I have two main questions about this.

1) Do I stand to gain quality and reduce problems on press by switching to Euclidean?
2) What would be the best way to do testing between the two?
3) Should plates be output without any dot gain curve to compare the two more accurately, or would using the current curve for both work just as well?

I hope this isn't a joke post...

1) No
2) There's not much point in testing the two.
3) Yup, whatever curve you're using now will work.

Terminology:

A Euclidean dot is a round dot that goes from round to checkerboard at 50% and back to inverted round in the shadows. Very basic screening that mimics camera-based screening.

See more info here:
http://the-print-guide.blogspot.ca/2...ot-shapes.html

Elliptical, what you seem to be using now, breaks the 50% optical bump of the Euclidean screen at 50% into smaller bumps at 40% and 60%

A better dot for offset with CtP plates would be a non-transforming round dot (as per the the URL link above).

Whoever told you to use Euclidean is, to put it politely, an idiot. Or uninformed.

 

[Luvdgoof]

Thanks for your response Gordo. No joke, seriously seeking answers. I came across that article while researching this but didn't get a definitive answer. While informative, what I took away was that all dots seem to have their pros and cons without really pointing to a solid recommendation. I would want to put a plate together with images and gradients similar to our more critical jobs using a few different dot types to see which works best. Based on your advice though, I should leave Euclidean off the table and do some testing with a round dot as well as with our current elliptical.

I'm curious about why the current GRACoL curve will work for testing the new dot. If the dots create different affects at the 40, 50 or 60% ranges, wouldn't the curve that's been specifically calibrated to correct dot gain for the elliptical dot throw off the color for the other dots? Sorry if these are basic questions. Things have been running the same here for a long time without anyone really knowing why, aside from "That's just how we've been doing it," so I'm trying to gain some clarity on it.

 

[walterz]

With all due respect Gordo, I hear what you are saying. I also understand that your responses are always based on a good press run. Yes the shape of the dot alone will not produce more/less problems. Each one works fine. However, from our experience we found that one will be more forgiving than another. During our early CTP days we tested Elliptical and found that any movement in the press would exaggerate the dot gain relative to the orientation of the elongated dot relative to the direction of movement. IOW if the movement was in the direction of the ends of the football shaped dot then dot gain was not very significant. If the movement was in the direction of the width of the dot, then it was very noticeable.

Luvdgoof - there is a way to get different images on the same page to plate at each their own line screen or screen angle. I have not recently worked with this so am not sure if you can change the screening method as well. You set the image specific screening information when making the PDF and then tell Prinergy output to honor the document settings / not override the screening.

 

[shorty83]

I work at a flexo shop and use Esko to create my plate files. The guy from Esko who trained me told me to use circular euclidean dots when creating plate files, I am not sure why though. Either way, I have not had any problems using it at this point and its been about 6 years.

 

[gordo]

Thanks for your response Gordo. No joke, seriously seeking answers. I came across that article while researching this but didn't get a definitive answer. While informative, what I took away was that all dots seem to have their pros and cons without really pointing to a solid recommendation. I would want to put a plate together with images and gradients similar to our more critical jobs using a few different dot types to see which works best. Based on your advice though, I should leave Euclidean off the table and do some testing with a round dot as well as with our current elliptical.

I'm curious about why the current GRACoL curve will work for testing the new dot. If the dots create different affects at the 40, 50 or 60% ranges, wouldn't the curve that's been specifically calibrated to correct dot gain for the elliptical dot throw off the color for the other dots? Sorry if these are basic questions. Things have been running the same here for a long time without anyone really knowing why, aside from "That's just how we've been doing it," so I'm trying to gain some clarity on it.

For CtP offset the best dot shape if you're using AM/XM screening is the round dot (non-transforming).
Benefits: Dot shape is the same for all screen angles and frequencies, optical bump is hidden in the shadows at the 75% tone, dot is non-directional so it is less affected by press problems. Reduces single channel moiré issues. Dot is non directional, i.e. all screen angle dots react the same to directional press issues such as slur and doubling.

With an elliptical dot the optical bump at 50% that a Euclidean (transforming round dot) dot shape exhibits is moderated by being split into two – when the dots first touch at the long width at the 40% tint and then again at the short width at 60%.
However, as walterz noted, the dot shape varies at different screen angles which can cause single color moiré and uneven dot gain. Dot is directional, at low lpi frequencies the “chaining” of the dots as two points touch can cause lines to appear as artifacts. Directional problems on press such as slur and doubling can cause strong tone and color shifts depending on the angle of orientation of the dots relative to the angle of the paper as it travels through the press.

Here are pics of the different dot shapes:

Euclidean:



Elliptical:



Round:


What happens at the 50% for Euclidean and at the 40%/60%) with Elliptical is an "Optical bump" - you see a dark line at those points. It's not dot gain in the sense that it can be fixed with dot gain curves. So from that point of view you can ignore it.
With today's screening engines most vendors have found work arounds to the 50% bump with Euclidean screens (e.g. taking a pixel out of one of the corners (as Agfa does) or slightly elongating the dots (as Esko does) when the dot transforms from round to square at 50% before going to inverted round. So you might not see the optical bump with your RIP.

And yes, if you're going to compare AM screens then compare Elliptical to Round. When you test, make sure you include causing a problem like slur to see how the different screens react.

(Please let me know if you cannot see the images when you're logged into PrintPlanet - there's sorcery goings on with attachments)

 

[gordo]

I work at a flexo shop and use Esko to create my plate files. The guy from Esko who trained me told me to use circular euclidean dots when creating plate files, I am not sure why though. Either way, I have not had any problems using it at this point and its been about 6 years.

Halftone screening is a mess when it comes to naming dot shapes. Esko does not use the same terminology as other vendors (including Adobe).

What most technical publications call a "Euclidean" dot Esko instead refers to as a Round (Fogra) dot. Round/square/inverted round. Here it is illustrated in an Esko screening guide:




What most technical publications call a "Round" dot Esko instead refers to as a "Circular (Euclidean)" dot. Round (non-transforming) through the tone scale. Here it is illustrated in an Esko screening guide:



The "Round" dot, a.k.a. Esko's "Circular (Euclidean)" dot is the dot shape specified by FIRST which is published by the Flexography Technical Association (FIRST calls it "Round Dot") ( http://flexography.org/product/first-5-0/ )

So when you say: "The guy from Esko who trained me told me to use circular euclidean dots" he's using Esko's terminology to refer to the FIRST specification for using a Round dot in flexo application.

(Please let me know if you cannot see the images when you're logged into PrintPlanet - there's sorcery goings on with attachments)