Author Topic: Halftone banding in PS when using bitmap to create halftones?  (Read 2369 times)

Offline mimosatexas

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I started noticing this on certain images and I am honestly clueless as to why it is happening.  Google is failing me completely...

I have tried TONS of different resolutions, LPI's, angles, shapes, etc and it is pretty much always happening with this image.  I can create a simple gradient and it just isn't happening.  When you zoom in super close it looks like the issue is the actual pixel shape of the dots is inconsistent, even at something like 5000ppi, which I understand is due to the size changing based on the % of the gradient at that point, but why is it banding in this way and so noticeably, even at super high resolutions?  Changing the angle/lpi/shape will change the angle and size of the banding, but it is always there.  It's super obvious on the film and in the print as well.

The attached images are the photoshop file zoomed out to a point exaggerate the effect a little, but the second one if pretty close to what it looks like.


Offline Colin

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #1 on: April 03, 2015, 02:27:58 PM »
Was this image a scan from pre printed materials like a magazine?

If so, it will pick up the artifacts from the rosettes used to print that image....
Been in the industry since 1996.  5+ years with QCM Inks.  Been a part of shops of all sizes and abilities both as a printer and as an Artist/separator.  I am now the Ink and Chemical Product Manager at Ryonet.

Offline Sbrem

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #2 on: April 03, 2015, 02:33:27 PM »
Here's what I do with those, it's worked so far. A raster image is made up of consistent pixels when created, you set the resolution and go. If creating art, a good rule of thumb is 300 ppi minimum at the final size. But this isn't that particular situation, we have to deal with it as is. So, I'll take a crappy jpeg someone gives me, convert to grayscale using the Black and White adjustment to control the shades. From here, I go to Bitmap mode, input resolution is a crappy 72 ppi of course, but set the output resolution to 1200; set the halftone to the desired line count, angle and shape. The high output resolution will make the resulting dots exceptionally clean. Trying to change the resolution of a raster image is rather fruitless, at least for me. I'd love to hear something to the contrary if there is a tip or two floating around out there...

Steve

Edit, just saw the above post, and yes, if you took that from a printed piece, there is not a lot you can do. The descreening filter found on a good scanner software may help, and you may have to blue more in Photoshop to make a new starting point.
I made a mistake once; I thought I was wrong about something; I wasn't

Offline lrsbranding

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #3 on: April 03, 2015, 03:30:26 PM »
Would cleaning up the image with this software-  http://www.benvista.com/  before going to PS help with the problem?

Offline mimosatexas

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #4 on: April 03, 2015, 03:41:24 PM »
The art is not scanned from print and the original image resolution is 300ppi.  I was wrong in my original post as well, it is happening no matter what, even on a simple gradient in photoshop.

Attached is an image of a test.  I made a 1200ppi image, added a 0-100% white to black gradient, then bitmapped into halftones, also at 1200ppi.  Again, regardless of angle, shape, lpi it is causing the banding.  what gives?!  It definitely did not always do this...and I haven't changed anything that I know of...

It must have to do with some math related to the way PS is creating the halftones.  the first image below is standard 22.5degrees 55lpi 1200ppi ellipse.  The second is 25degrees 50lpi 1200ppi round.  third image is zooming in on the halftones around the 10% range.

Offline Sbrem

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #5 on: April 03, 2015, 03:45:07 PM »
Well then, that is a tad bizarre...

Steve
I made a mistake once; I thought I was wrong about something; I wasn't

Offline mimosatexas

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #6 on: April 03, 2015, 03:55:46 PM »
Yea seriously.  I have no idea why it is happening...

I've used this method for YEARS without this happening.  I've noticed it occasionally on certain prints in certain areas before, but chocked it up to a film issue and it wasn't ruining prints, but the last few jobs it is noticeably happening in photoshop and it definitely noticable in the prints.  Maybe I am just more sensitive to it now that I see it, but it is driving me nuts...

Offline Dottonedan

Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #7 on: April 03, 2015, 04:12:00 PM »
I'll have to look later, in Photoshop and do some comparison, but it could be related to or a result of pixel aspect ratio. Not sure if this is even the tight area in thinking of, but I'm referring to you pdf pixel dimensions. You have options when opening a file or creating new art (for a desired purpose or target). We don't normally get into this, but it's there. It may be to accommodate different input sources like camera formats etc. (again guessing). If accidentally changed from default, or digging and playing with options some time ago, it may be presenting odd patterns that conflict with various angles. I'm only reaching here, but seems feasible.

Certainly related to settings in psd. That's why a True RIP is better than the psd halftone method but it works. Just have to deal with this type of stuff sometimes. Ps dots are also not consistent in line count. It's really based on resolution. For example, a 50 lpi at 300 ppi will come out with maybe 49, 50 or 51 lines. 600 ppi may come out with other numbers of lines per inch. All i'm saying is it not totally accurate but makes no real difference in print.
Artist & Sim Process separator, Co owner of The Shirt Board, Past M&R Digital tech installer for I-Image machines. Over 28 yrs in the apparel industry. Apparel sales, http://www.designsbydottone.com  e-mail [email protected] 615-821-7850

Offline Squeegie

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #8 on: April 03, 2015, 04:21:45 PM »
I had been using the bitmap conversion in PS for a long time without any issues. Then, one day, I had the same or virtually the same banding/moire issue. I could not make it go away.  I tried countless DPI and LPI combinations with no success. 
I think I even had a discussion with DottoneDan about it.

The end result for me was to break down and buy a RIP.  I am now using the T-Rip software with outstanding results...from within any program.

Best of luck,
Bill

Offline Dottonedan

Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #9 on: April 03, 2015, 05:18:15 PM »
I had been using the bitmap conversion in PS for a long time without any issues. Then, one day, I had the same or virtually the same banding/moire issue. I could not make it go away.  I tried countless DPI and LPI combinations with no success. 
I think I even had a discussion with DottoneDan about it.

The end result for me was to break down and buy a RIP.  I am now using the T-Rip software with outstanding results...from within any program.

Best of luck,
Bill

I'll 2nd the outstanding results. ;)

Artist & Sim Process separator, Co owner of The Shirt Board, Past M&R Digital tech installer for I-Image machines. Over 28 yrs in the apparel industry. Apparel sales, http://www.designsbydottone.com  e-mail [email protected] 615-821-7850

Offline mimosatexas

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #10 on: April 03, 2015, 07:12:19 PM »
Ok, found one that works for the most part.  The banding pattern thing is still there, but very minimal.  1200ppi, round, 45lpi, 105degrees.  Shrug...

Offline Fluid

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #11 on: April 04, 2015, 08:47:58 PM »
Ghistrip is free and works pretty darn well for halfton printing. Wouldnt use it to rip colors yet for printing halftones is does a good job. A google search should yield locations for downloading.  Worth a try. 

Richard Reilly - Fluid

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Offline Fluid

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Re: Halftone banding in PS when using bitmap to create halftones?
« Reply #12 on: April 04, 2015, 08:48:12 PM »
Ghostrip - Ghostview

Richard Reilly - Fluid

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