Is possible to change the dot size in the diffusion dither?

[NeroInferno]

Hello,
When I convert my documento into Bitmap and I select the "Diffusion Dither" with a frequency of 187 ppi I have my dots of the same size. I know in frequency modulation the dot size must be the same but is possible to change THAT dot size in the way all the dots will be the same size but a little bigger?

I've read the dot size is dependant from the resolution of the file, but I can't see any difference with the naked eye if I use an artfile at 200ppi or 300ppi.

Should I play with the dot gain settings or like it's a variable I can't control?

Thank you,
Fabio

[{LG}]

Yep, your square dots will get larger as your ppi goes down (less pixels per inch) and visa versa. If you want to adjust after that, you could save each plate as a bitmap and do a select and contract on the pixels to choke 'em up.

My experience with FM or square dots is on textiles and last time around, I ran at about 175ppi, saved each color as bitmap, outputted normally and printed wet on wet on the press. At 175ppi a 300 HD (thick thread) mesh held the dots. As you get that ppi up there you'll need a higher mesh count and probably some thinner threads. The gain is actually really beneficial printing wet on wet as it creates a blending effect and makes the impossible feat of perfectly registering the interlocking dots a non-issue. Since this is a flatstock forum you won't have that advantage I would imagine but the overlapping of the dots, presuming you have somewhat transparent inks over other dry dots could create a similar blending via the transparency and the right print order.

What are ya going for specifically?

[NeroInferno]

Hello!
thanks for the reply.

Scaling a bitmap won't create antialiasing? In this way however I believe you can't control anymore the right size of your dots!

I haven't understood what's your original file resolution (PPI).

Do you print wet on wet with plastisol inks?

what do you mean with "I would imagine but the overlapping of the dots, presuming you have somewhat transparent inks over other dry dots could create a similar blending via the transparency and the right print order.
"?

For the textile I have a 255 threads/inch mesh, and I'll try to burn a 187ppi artline, single color (black plastisol), on fabric. I hope the 255 mesh will hold the 187ppi.

Oh another thing: what about off contact? theorically printing on contact more colors could work for trapping, but printing a single color won't be better to add off contact?

Thank you
Fabio

[{LG}]

Not suggesting you scale the bitmap. When working with any raster file, always start with the artwork at size. What I meant was, run the index routine and then save each color as it's own bitmap file. If you want to choke or spread a particular colors pixels you can select all your pixels and do a select>modify>contract (or expand). You can even place these bitmap .tiff files into illustrator and add in your vector text, etc. and output from there if you like.

Helpful links for index seps:

Index Separations Tutorial

index separation

Index Sep. Printing - Translating DPI or PPI to square dot size? *older post on a T shirt forum that has a decent discussion on ppi, dpi, lpi in there

Typically your original file resolution is going to be higher (hopefully!) than 175-180ppi. For indexing though, like I mentioned, you need to have a lower ppi to get the dot size where you can hold 'em on the screen.

Yes, we print wet-on-wet as much as possible. We use phthalate-free plastisols and a little bit of water based inks.

what do you mean with "I would imagine but the overlapping of the dots, presuming you have somewhat transparent inks over other dry dots could create a similar blending via the transparency and the right print order.
"?

You can just disregard that, I wasn't sure if this was going on flatstock or fabric. What I meant was that there's still a little benefit to the square dot gain presumably even when drying between each color, provided your inks have some transparency to them.

Go higher with the mesh I think, but it doesn't hurt to try the 255 tpi. If it works then that's awesome.

Always print off contact on textiles and especially with plastisol. Always! How much off contact you use depends on your mesh tension, stencil thickness and your substrate.

If this is a monochrome print I wouldn't actually recommend the square dots unless you want the grainy/pixelated sort of look. Round dots and ellipses at 55lpi or more work best for me when printing single color.

Hope that helps!

[NeroInferno]

Hello LG,
thanks for the reply. I'll try the stochastic dots then I'll try halftones. The reason for the 255 t/inch is it's he only hig mesh screen I've for textile, the 300 t/inch ones I've are too much big for the carousel!

Thank you another time, I'll keep you updated.
Fabio

[NeroInferno]

Typically your original file resolution is going to be higher (hopefully!) than 175-180ppi. For indexing though, like I mentioned, you need to have a lower ppi to get the dot size where you can hold 'em on the screen.

Just another thing: I don't understand if you have an original higher resolution file, like 400ppi, then you downsample it to 300 ppi, make your index separation and then you convert it to bitmap, giving an output of 175ppi, or if you have an input file lower than 300ppi and then you make your seps. I know smaller is the resolution bigger will be the dots, but I'd like to understand if starting from a 300ppi will be difficult to hold the future square dots point on the mesh.

Thank you!

[{LG}]

Just another thing: I don't understand if you have an original higher resolution file, like 400ppi, then you downsample it to 300 ppi, make your index separation and then you convert it to bitmap, giving an output of 175ppi, or if you have an input file lower than 300ppi and then you make your seps. I know smaller is the resolution bigger will be the dots, but I'd like to understand if starting from a 300ppi will be difficult to hold the future square dots point on the mesh.

Thank you!

Well, I usually start at whatever res the file is, higher the better of course. Do all your normal PS adjustments and then save a copy and kick it down to the ppi you need for the index seps. That answer your question?

Goin back to halftone dots...
There's a old rule of thumb of dividing your tpi by 4 or 4.5 to get the proper lpi that can run without moire. It's not very accurate since thread diameters vary but somewhere to start if you want to do halftones. Along these lines, and from actual experience, I'd do the monochrome printing at 55lpi and maybe play with different angles to see what looks good but it's hard to go wrong with 22.5 degrees. You can choke back your halftone dots with that method I described above or just use curves before bimapping.

[NeroInferno]

Well, I usually start at whatever res the file is, higher the better of course. Do all your normal PS adjustments and then save a copy and kick it down to the ppi you need for the index seps. That answer your question?

So before you'll convert an artline at 175ppi to Bitmap using the "Diffusion Dither" method, you'll convert the file at the same PPI of the diffusion dither you're going to process?

Thanks,
Fabio

[{LG}]

So before you'll convert an artline at 175ppi to Bitmap using the "Diffusion Dither" method, you'll convert the file at the same PPI of the diffusion dither you're going to process?

Thanks,
Fabio

Yep, I think so, if I'm understanding you correctly. If your going to use a threshold bitmap might as well use the "threshold" adjustment to get more control.

[Edward7]

Thanks for the information.

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