Moire on print but not on PDF? What to do?

[Mads10000]

Hi Photoshop Gurus

I have moire on these images even-though it looked perfect before print? Is there a way i can make a preview that reveals the "hidden" moire?

I view it in printview on photoshop(calibrated to my imac screen) "there was a little moire" then saved it as PDF "then no moire" opened pdf in same size as printsize. How can something looking perfect turn out so wrong?

See the pictures where i compare it.

Hope you have tip or 2. Hard to find people that knows this workflow. I would like to have a bulletproof moire workflow if possible.Thank in advance.

 

[Tom Mann]

The first thing you have to do is determine where in your workflow the Moire pattern first was introduced.

In particular, if it arose at the time the images were captured, then the photography has to be fixed. This is because it's very difficult to remove Moire once it has corrupted an image. Once can get lucky and occasionally conditions may arise to minimize it once it's there, but you can't count on these.

OTOH, if the Moire was introduced at some late point in processing the image, then, usually only a small change in your workflow will need to be made. So, lets figure out whether it was in the original photo. The easiest way to do this is if you crop out a small section of one of the original photos (that is giving you trouble), and post it here. A few hundred pixels on a side is plenty.

We'll take a look at that, then figure out what to do.

Tom M

 

[Mads10000]

Hi Tom

Ok, i don't think it's original image.But i think the small resizings from file to print sometime make the trouble, hmmm. 100% and Printsize view.
Does these images show something?

 

[Mads10000]

Any Guru on this website?

 

[thebestcpu]

Hi Mads
Sources for Moiré can be from a variety of sources. Since you 100% view did not show any issues I strongly suspect that this is all caused by the specific resampling percent and algorithm used.

If you have a repeating pattern in the source pixels and resampling is done in a fashion that resizes so the sampling is done at about the same frequency as the pattern it is not hard at all to get Morie.

Since I did not have your full original, I took your 100% sample, flipped it vertical and tiled and then horizontal and tiled. The I created a Photoshop pattern and did a fill on a 4000 x 4000 pixel image. Noticing that some of the repeating vertical white lines in your original were at every 7 pixels, I resized by 1/7 using nearest neighbor reampling option and the image below is what resulted at 100% viewing.

I suspect that the resizing done somewhere along the line (could even be in your printer driver) could cause this. (click on thumbnail)


Very quick and easy to generate Moiré.

There are a variety of ways to avoid the issue.
- create a version of your image resized in Photoshop (or most desired editor) and try a couple different resampling algorithms.
- If you print is of a size where you will not be able to see the fine threads anyways, do a 1 pixel or so blur on the image so there is less of a pattern in the first place to create the Moiré pattern by resampling
- Check the options for resizing in the PDF options. A fair chance that is involved as well.

Hope the above suggestions help you make some progress.