Dialing In Curves with I-Image

[ffokazak]

Hey guys,

My screen guy asked what the process is for experimenting with the curves on the I-Image.

I can tell him what I think.. Or I can ask you pros

We have started at 80/60 and are getting great prints.  I am ever searching for better and better.. so where do we go from here?

I-image w Chromablue, and a Tri Light ST 6K

Thanks!

[blue moon]

the rocket launcher?
which RIP?

pierre

[Colin]

Do you want to create a correct halftone dot on your screen?  A 50% tone prints on screen as a 50% dot?

Or compensate for physical dot gain on the shirt, by curving back the halftone print out on the screen?  A 50% tone prints as a 30-35% dot?

We compensate for physical dot gain in all separations and let the rip print normally.  I.e a 50% tone will print on screen as a 50% dot.  But I will scale it back in my separations so it looks correct when it hits the shirt.

[zanegun08]

We compensate for physical dot gain in all separations and let the rip print normally.  I.e a 50% tone will print on screen as a 50% dot.  But I will scale it back in my separations so it looks correct when it hits the shirt.

I don't understand this, do you first separate the image like normal, and then at the end scale back the channels?

Or do you have photoshop settings to re-compensate for dot gain?  So your 30% in photoshop displays as a 50%.

Seems confusing, and more intuitive to have the separation on screen give the result you want, and have the rip do the adjustments, otherwise the separation would look washed out on the computer.

[ffokazak]

I image ST

Hmm thats a good question. Seems like the ideal situation would be to print a offset dot that gains on press to where it needs to be...

[Dottonedan]

I do have my Photoshop dot gain settings for spot color and grayscale set to 35%.  This way, as I build art and seps, I'm building them lighter than needed.  Always better to do things on press to make things print lighter. You can add, but it's hard to take away from gain.

Then, in my I-Image RiP, our curve is set to make up for the excessive gain of a 3 head machine. The standard 80/60 is in no way good enough. Not even for a 1 color halftone print. Your shadows fill in near 70% so you need to cut that shadow range back to like 75-80 in the 95% area.

This is all visual. Not intended to make an acurate dot % of 95 in the 95. It's intended to have open shadow in the 95.  So just keep adjusting until its pretty dark when printed on the shirt...but still dots.

The only way you will get an accurate % is by measuring your gain (with a densitomitor) using a halftone printed test onto a shirt and getting 3-5 test results and average those. Then go back and adjust for that.

Still, this would be a result based on one scenario. For example, you would need several test results and adjustments, for say...sim process on cotton tees. Another for poly. Another for discharge, another for heavier sweatshirts using sim process (ifyou want to get accurate).

In our shop, we don't print CMYK even for contract orders, we do not need to be dead on in %.  We just get it to look good. We achieve that. I would however like to use the densitomitor test results just to be ready for that one day when someone wants a dead on accurate representation using 4 clr process....but who does that?  Not many, and none of our customers at our shop.

[Colin]

We compensate for physical dot gain in all separations and let the rip print normally.  I.e a 50% tone will print on screen as a 50% dot.  But I will scale it back in my separations so it looks correct when it hits the shirt.

I don't understand this, do you first separate the image like normal, and then at the end scale back the channels?

Or do you have photoshop settings to re-compensate for dot gain?  So your 30% in photoshop displays as a 50%.

Seems confusing, and more intuitive to have the separation on screen give the result you want, and have the rip do the adjustments, otherwise the separation would look washed out on the computer.

Yes, all separations are created with dot gain in mind.  Dan stated it very well.

Otherwise, you will need to dial in a dot gain setting within your rip for each halftone lpi you want to use.  40 lpi will gain much less than 55 or 60lpi.  As Dan pointed out, also for each different shirt fabric type, ALSO for inks printing directly on the shirt versus over a white base plate, vs over a discharge base.....

Far simpler for the artist to compensate at the source knowing what is going on on press.  Hopefully you have artists who can grasp the concept, learn, and then execute properly.

I should point out that my I-Image is a single head machine set up for BEST QUALITY, so we had very little adjustment.

[photoscreenprint]

Dan said it pretty well. If you are printing your separations from Photoshop then that is the best place to set up your dot gain curves for the press. This way the separator can compensate for the gain visually and get a decent preview of the intended result. This also allows you to print color comps from a multi-channel color separation which includes all the color and gain information. I have found that with a calibrated Photoshop, I can hand the printer a color comp complete with color swatches for each ink, printed directly from a multi-channel color separation to a calibrated color printer, and match it on press pretty much every time. I also tend to go high on the gain, with my gain set to 38%. (50% displays at 88%)
 Gain curves on the Rip itself can then be used to compensate for the gain from the DTS or film output only. With this approach you can use the Rip curve to get your imaging devices aligned so they have similar output, which can be helpful if you have a second or backup device. With only one output device you can kinda bundle the press gain and device gain into a single value in Photoshop's color settings.

[milothegoat]

This question may go unnoticed since this post is so old, but when you guys say things like "we started at 80/60," what do you mean? Are those the input/output values in the I-Image rip curve?