Compensating for Dot Gain

[Roxy]

Hi,

I'm kinda new to this and prepress as a whole. I come from a graphic design background but have recently moved into more of a prepress capacity. Can anyone shed some light on how I might compensate for Dot Gain on a Harlequin 7.0 RIP? We've established how much gain by printing a test strip but now I'd like to know how to input this into the RIP such that it makes the adjustments?

Roxy

[G_Town]

Hi,

I'm kinda new to this and prepress as a whole. I come from a graphic design background but have recently moved into more of a prepress capacity. Can anyone shed some light on how I might compensate for Dot Gain on a Harlequin 7.0 RIP? We've established how much gain by printing a test strip but now I'd like to know how to input this into the RIP such that it makes the adjustments?

Roxy

It's been years since I used a Harly but I think it's just a matter of coming up with a Look up table to adjust for dot gain.

Someone will be with you shortly who can answer more specifically.

[Joe]

We don't use a Harlequin but we adjust our plate curve for it.

[DigitalCrapShoveler]

My manager is very anti-plate curves, or RIP curves for that matter. I end up doing a lot of curve corrections depending on press in PS. I hate it, but I don't make the decisions.

[Roxy]

I see the "table" on the RIP.

example - I printed a target page without any compensation on the RIP so plates we're 1 for 1. If I read the printed Cyan 75% target with a densitometer it gives me 90%. Would I simply put 90% in the 75% field in the table on the RIP. Is it that simple? I know there are many other variables especially when its on press and being printed but I'd first like to know if I'm tackling the RIP part in the correct manner.

Thanks for any help guys!

Roxy

[DigitalCrapShoveler]

I see the "table" on the RIP.

example - I printed a target page without any compensation on the RIP so plates we're 1 for 1. If I read the printed Cyan 75% target with a densitometer it gives me 90%. Would I simply put 90% in the 75% field in the table on the RIP. Is it that simple? I know there are many other variables especially when its on press and being printed but I'd first like to know if I'm tackling the RIP part in the correct manner.

Thanks for any help guys!

Roxy

I think you would need to go the other way, so I am guestimating at this, your 75% reading a 90% would mean you need to set it at around 60-62. You are roughly getting 15-20% dot gain. And... it really all depends on substrate. Offset paper will have much higher dot gain, I have seen 40%. You are going about it the right way, though coming here, some of these guys are freakin' masters of the Prepress.

I should point out I have never used a Harley RIP, so I am basing this on experience with other RIPs.

Now that I think about it, you may be correct. If you are creating a curve, you would need to place the value you are reading in the corresponding field. So yes, 90 would go in the 75% field and so on.

[almaink]

Are you outputting plates or film? To many variables for you to do it yourself IMO running direct to plate. Your better off if running film just running linear as each press will be different, and even then different things can and do effect dot gain. Before we went direct to plate here I had my film running linear and compensated for each press using Photoshop for bitmaps. Highlight set to 2% and shadows set to 93%. Process work tho is tricky and I did it on a job by job basis by the seat of my pants.

[Roxy]

I guess I should have mentioned that we are CTP, Trendsetter 150 in fact.

[Roxy]

Hey Digital,

If you're first assumption was to go the other way...how was it you came up with 60-62? In other words, whats the math there? This is exactly my conundrum - I'm not sure how the RIPS calculate this information so...up...down??

[DigitalCrapShoveler]

The first part was taking away dot from the 75% by reducing what your 75% prints. If you are reading 90 on a 75% then logically you know there is about a 15 point jump. If you do the math and take the equal percentage off of 75% to accomodate the dot gain then you end up with 60-62%. However most RIPs today want you to put in what your reading so it can do the curve correction for you. Understand?

[Roxy]

OK - Gotcha

But are you also saying that a modern RIP should work as I suspected...that one could simply plug in a 90 in the 75 field and the RIP would make the necessary calculations? It would seem logical that a major player like Harlequin would have built that into a RIP...especially a pricey one

[DigitalCrapShoveler]

Yes, that is exactly what I am saying. You got it.

[Roxy]

Thanks Digital - Appreciate the help. Now its back to more testing - I suspect that the deviations and inconclusive readings might be more related to the press itself but I still wanted to work the entire "process" to see where things are wonky. The platesetters appear to be imaging fine...so I'll be looking at the press -  blankets, ink and fountain solution next...

[DigitalCrapShoveler]

Good start... sounds like you're on you way.

[Gutnbg]

One day we were messing with this and couldn't remember which way the curves went. Finally somebody was brilliant enough to say, "you know if it's wrong we can always go back the other way."


And Shoveler, may I be the first to offer an assessment of your higher-ups for compensating for dot gain by changing photoshop files? I mean I understand if your total ink is all wrong, but to change the curves in the individual pieces of art instead of adjusting the output device to compensate for the device being out of synch can charitably be called "less than inspired."

And I'd bet I'm a lot more charitable than you were in this situation.  :wink:


Roxy: welcome, and good luck with this stuff. We're here to help and can provide references.  :grin: