Minimum halftone pixel size?

[Paulio]

Hi guys!

Got a question here which is baffling me a tad.

I'm trying to convert a greyscale design I made a while back for use on a t-shirt, using a single colour halftone. I thought it was going peachy, but apparently the guys who are printing it reckon that some of the dots are far too small.

For reference, here is a sample of the original:



Here it is after running through a halftone (300 dpi, 55 lines per inch, 22.5 degrees):



Here it is again after running it through a halftone at 40 lines per inch this time:




As you can perhaps see, some of the dots seem to be only a pixel in size, despite what I do with the settings.
Is there any way to specify a minimum pixel size for the halftone dots?

Thanks in advance for your help guys.

 

[Renegade]

Resize your grayscale image to be the exact print size at 300dpi. Then, convert to bitmap. (Image > Mode > Bitmap. It should show the 300ppi input, make sure Output says 300ppi and method is Halftone Screen, click ok. Set your frequency to 35 lines per inch, angle at 70, shape as ellipse.

 

[Paulio]

Resize your grayscale image to be the exact print size at 300dpi. Then, convert to bitmap. (Image > Mode > Bitmap. It should show the 300ppi input, make sure Output says 300ppi and method is Halftone Screen, click ok. Set your frequency to 35 lines per inch, angle at 70, shape as ellipse.

Hi Renegade! Thanks so much for your help, but unfortunately the problem remains.

As you can see from this pic, your advice largely helped, but there are still halftone dots which are still 1px.



Is there any way at all to change the minimum dot size?

Thanks again

 

[Tom Mann]

Perhaps I don't understand the issue completely, but, for a given set of half-tone process parameters, since the smallest half tone dots correspond to pure black, and you want to have only dots larger than a certain size, why don't you just set the minimum black level of the source image to something like rgb = 30, 30, 30 and you won't get any dots smaller than the corresponding size.

Tom M

 

[Paulio]

Perhaps I don't understand the issue completely, but, for a given set of half-tone process parameters, since the smallest half tone dots correspond to pure black, and you want to have only dots larger than a certain size, why don't you just set the minimum black level of the source image to something like rgb = 30, 30, 30 and you won't get any dots smaller than the corresponding size.

Tom M

Hi Tom! Thanks for the reply.

While that certainly makes the minimum dot size much more to my needs, it also means that where I want the halftone to end, it keeps going, like so:



Thanks again for your help so far. It's such a frustrating problem. I'm sure there must be a simple answer here but I'm just not seeing it.

 

[Renegade]

It looks to me from those tiny dots as if you're image is still sampled too high? It should be resampled to around 10 inches wide at 300dpi, in grayscale mode.

 

[Tom Mann]

"While that certainly makes the minimum dot size much more to my needs, it also means that where I want the halftone to end, it keeps going, like so: ..."

Well, then what about making a simple curve that maps any pixel darker than 30, 30, 30 to 0,0,0 (which should completely shut off the tiny half tone dots), but values above 30,30,30 retain their original value, and hence, decent sized half tone dots.

?

Tom

 

[Renegade]

+1 on Tom's suggestion.

Another thought; just send the grayscale image over to the tshirt printer and let their RIP software convert to their optimal line screen setting. They usually know what they're doing when it comes to converting art for their printing needs.