round halftone screen coming out square

[rainyseason]

Hi guys,
I'm new to this forum and have an issue that I can't seem to figure out. Much thanks to anybody who can shed some insight into what might be going on.

I'm working on a poster design and trying to use halftones for the first time to acheive kind of a retro thing and maximize a minimal color palette for screenprinting. My problem is that I want round halftone dots and they keep coming out square shaped for some mysterious reason I can't understand.

The method I am using is this:

• select areas within my line art with the magic wand tool,
• save the selection into a new document
• fill with black
• change mode to greyscale
• lighten the black to a light grey
• convert to bitmap
• choose "halftone screen" with the same resolution as the document. I'm entering 45 for all angles and playing around with the size of the halftone dots until I find something appropriate
• invert, copy and paste into a new alpha channel in the original art document
• load as selection, create a new layer and fill with the desired color

For some reason, my first attempts at this were successful and yielded the effect I wanted The dots were a little square-ish, but looked okay for what I wanted:


However, when I started repeating the exact same procedure in other areas, the dots were completely square, like this:


Any ideas of what I might be doing wrong?

Thanks,
Trey

 

[Tom Mann]

That's weird. Rather than try to figure this out by having to ask a million questions, probably the quickest way to get to the bottom of this would be if you could simply post your PSD files. To save space, they can be small crops of an area of interest and its immediate surroundings. Also, if the forum uploader doesn't like a PSD file, just zip it, and that will get it through (provided it/they are not huge).

Tom

 

[rainyseason]

Hey Tom,

Thanks for the reply. I'd be happy to upload the .psd file for you but I'm a little ashamed to admit that I have no idea how to do that. The only way I can see to upload into a reply here is the insert image button and that only allows jpeg, png, and gif files. I've saved a smaller version of the psd, so size shouldn't be a problem, but could you walk me through how to attach something like that to a reply on this forum?

Trey

 

[rainyseason]

I've read a little bit more and realized that to attach a psd you have to forgo the "quick reply" and go to the "manage attachments" but I'm not having any luck there either. I've tried repeatedly to do this by clicking "add files", but after I browse to the file on my computer and click upload, it looks like it's uploading for a second then nothing happens. It says it allows psd files up to 30 MB and mine is only 25 so I don't know what the problem is.

 

[hawkeye]

What channel settings are you using for the screen angles in the filter?

 

[rainyseason]

Hi Hawkeye, 300 ppi (same resolution as the document) 45 degrees, round halftone screen, I believe 10 lines per inch, but it might have been 20

 

[Tom Mann]

I've read a little bit more and realized that to attach a psd you have to forgo the "quick reply" and go to the "manage attachments" but I'm not having any luck there either. I've tried repeatedly to do this by clicking "add files", but after I browse to the file on my computer and click upload, it looks like it's uploading for a second then nothing happens. It says it allows psd files up to 30 MB and mine is only 25 so I don't know what the problem is.

Here's a nice tutorial on how to upload attachments (eg, files that are not immediately recognized as image files such as zip, rar, Word, etc. files): http://www.photoshopgurus.com/forum...s-forum-help/32698-how-upload-post-files.html

BTW, you can skip step #7 in the tutorial, and go directly to step #8. Then you can hit either the "Preview" button, or the "Submit Reply" button, and you are done.

Give it a try.

Tom

PS - Here are two other related threads that may also be of use to you:
http://www.photoshopgurus.com/forum/photoshop-newbies/27838-attachment-order-posts.html ; and,
http://www.photoshopgurus.com/forum...6-types-attachments-you-can-upload-forum.html

 

[rainyseason]

Thanks again, Tom. I followed those instructions to a T but still no luck with uploading my 25 mb psd file, so here it is in a .rar file:

 

[Tom Mann]

I think the answer is quite simple.

First, notice that the shape of your halftone patterns are all somewhat different:



Next, let's make up a simplified situation to make it easier to see what is going on. Let's make a gradient from pure white to pure black, and convert it to a halftone pattern using almost the same recipe you described in your previous post. The only difference was that I made the screen frequency lower to make it easier to see the shapes of individual dots.



Notice that starting from the top and working our way down, the pattern goes from round white dots on a black background. These get bigger until the 50% point (at which point they have to become square to give a 50% fill), and then it turns into rounded black dots on a white background. You may find it instructive to repeat this exercise using other dot shapes. For example, diamonds make for a very interesting pattern with a gradient like this.

I think the reason you are running into the differences in shape that you are seeing is because (quoting from your message), "...and playing around with the size of the halftone dots until I find something appropriate...", so they have to wind up having different shapes.

Does that sound like what's going on to you?

Cheers,

Tom M

 

[rainyseason]

Thanks for the input, Tom. I didn't know that they turned to squares at the 50% point, but I'm not convinced that's what's going on here. The reason you see some completely round dots (the shading and highlight areas on the stein, belly, wine glass, and tuba is because I used a different halftone technique on those areas. For those spots, I created a layer and filled it with grey, then went to filter> pixelate> color halftone and created a channel filled completely with those round halftone dots. I then loaded it as a selection and painted through it with the paintbrush just over the spots I wanted shading or highlights. I decided to use the other technique for the large flat areas of halftone because it seemed more precise and efficient than trying to paint in those whole areas with the paintbrush.
When I mentioned I "played around with the size of the halftone dots" I simply meant that I tried various sizes from 10-30 lines per inch to see which size looked most appropriate to the artwork before choosing the right one and I could'nt remember exactly which size I went with. I think it was either 10 or 20, but I'm pretty sure I went with the same size for all the flat areas and I don't remember 10 being any more or less round than 30. Basically, after that very first area that I did it with (the yellow skin halftone) all attempts to use the first technique I described in the post, yielded square dots, regardless of the size settings I tried. However, I'll go and try a few more halftones with various sizes and see if your theory holds any water. Thanks again.

 

[Tom Mann]

Unfortunately, this has to be short ...

Jusr one comment: for a given shade of gray, changing the size of the halftone spots won't change their shape, just their size. I thought u inadvertently changed both their size and shape by adjusting the underlying gray level to get the size u wanted.

The method u described involving selections is more likely to yield round dots on this scale because many selection paths are slightly smoothed / anti-aliased.

Gotta run.


T

 

[rainyseason]

Yes, I think you nailed it there, Tom. After I wrote the last reply, I started thinking that it's probably not the lines per inch, but the fact that when creating the halftone, I was always using very close to 50% grey. I'll try going lighter or darker next time and I'm sure that will fix it. I think the problem is that I learned this technique through a chapter in Derek Lea's book Creative Photoshop, in which he was using 50% grey but he was using line halftones instead of dots. I never stopped and put 2 and 2 together about how that would affect the shape of the round dots. Thank you so much for helping me figure this out!

 

[rainyseason]

update: just nudging the value up a little bit lighter than 50% grey resolved the issue and now I have perfectly round halftone dots!

 

[Tom Mann]

That's great! Glad to have helped.

The best of luck with your project. Do check in from time to time and say hello.

Cheers,

Tom