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Author Topic: dot shape and dot gain  (Read 3166 times)

Offline balloonguy

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dot shape and dot gain
« on: June 14, 2017, 08:14:43 AM »
I am not sure if this should be in art or printing or all 3...
Does anyone know of a direct correlation between dot shape and dot gain with half tones? I printed this simple grayscale photo on balloons. I have been having some issues with dot gain in last several months. The only change in my procedure is that I am about 300 miles north of my old shop. I made several films and screens to get this job looking good. My last change was dot shape. I have been using elliptical dots for a decade. I can't tell you why. It is just what I have been doing. After multiple adjustments I decided to change the dot shape. The print came out worlds better than the same settings with a different dot shape. I have not had an opportunity to explore it any further. I would like to know if anyone else has noticed this or has a strong opinion either way about dot shape.
These films are both 45 lpi at 45 angle burned on 305.
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Offline mimosatexas

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Re: dot shape and dot gain
« Reply #1 on: June 14, 2017, 08:45:00 AM »
I recently switched to round instead of ellipse as well and everything is printing much better for me.  I typically am using 50lpi on an epson 4800 through Accurip.  I have not really spent any time calibrating anything.
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Offline blue moon

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Re: dot shape and dot gain
« Reply #2 on: June 14, 2017, 08:48:10 AM »
elliptical is supposed to help eliminate the problem you have. 'not sure what is going on there, could be the RIP, the dot gain setting or something else.

pierre
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Offline Sbrem

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Re: dot shape and dot gain
« Reply #3 on: June 14, 2017, 08:52:56 AM »
The reasoning behind the elliptical vs round or square dots was to eliminate the sudden tonal bump that occurs at 50%, use square dots and you get a checkerboard, where all dots meet at all four corners. Dot gain usually causes a rather severe tonal jump there;  elliptical dots only meet at 2 corners, so theoretically, you get a smoother gradation. Something is fishy here...

Steve
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Offline ScreenFoo

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Re: dot shape and dot gain
« Reply #4 on: June 19, 2017, 07:51:08 PM »
Sure you didn't accidentally grab a bullnose squeegee?  ;)

Seriously though, that top image looks like there was no gain curve applied.

I've never seen anything more than the slightest differences between round and elliptical, even with the same gain curve...
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Offline Orion

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Re: dot shape and dot gain
« Reply #5 on: June 19, 2017, 08:36:57 PM »
Try changing the angle to 22.5, that should help, no matter which dot shape you choose.
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Dale Hoyal

Offline Squeegie

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Re: dot shape and dot gain
« Reply #6 on: June 20, 2017, 02:27:34 PM »
It also looks like the first image is lacking dots in the forehead area compared to the second image.
I would think there is a setting saved somewhere with the first image that has a bad curve associated with it.  Maybe selecting the new dot shape went to a default curve that worked better?
Just throwing out thoughts...
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Offline blue moon

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Re: dot shape and dot gain
« Reply #7 on: June 20, 2017, 04:38:29 PM »
Quote from: Squeegie on June 20, 2017, 02:27:34 PM
It also looks like the first image is lacking dots in the forehead area compared to the second image.
I would think there is a setting saved somewhere with the first image that has a bad curve associated with it.  Maybe selecting the new dot shape went to a default curve that worked better?
Just throwing out thoughts...

This seems like the best explanation so far. . .

Pierre
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Offline balloonguy

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Re: dot shape and dot gain
« Reply #8 on: June 21, 2017, 08:43:43 AM »
The print settings are identical and I used the same squeegee. They were even on opposite ends of the same screen. I am doing my best to compare like process (other than dot shape) The missing dots on his head was caused by the ink drying in the screen. This is a fast drying solvent ink being printed on mylar so there are some HUGE differences compared to printing shirts. I almost always scrap a few pieces setting up then clean the screen completely and print pretty fast...
I really have not had too much to play with this any more. It has been a crazy 10 days!
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Offline Squeegie

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Re: dot shape and dot gain
« Reply #9 on: June 21, 2017, 09:08:55 AM »
Not an answer as to why...but if all settings are the same with exception to the dot shape, and these is the results...I would start using the round dot and carry on smartly.
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