Where might this screen grid be coming from?

[dgberg]

A new one for me. The grid is not in the file on screen but when printed you can easily see it.
I missed it and sent the print to the client and of course she brought it to my attention.
Tried two different papers with the appropriate profile and it is on both. Could it be something in the way it was processed?
Printing with Lightroom Classic on a Mac 15.1.1

[dgberg]

I found the issue, noise. The noise in the image when removed with Topaz Denoise makes a perfect print.
Have never seen an images noise printed as a pattern like that. Most times you get an exact reproduction of the noise you are seeing not something else.
Any ideas?

[degrub]

Maybe from previous compression/resizing or same in the printing pipeline ?
Looked a little like moire' patterns.

[aaronleitz]

That's really weird.

A year or two ago I bought Topaz Gigapixel AI to uprez some images for large printing and the process left a strange grid artifact in the images similar to what you're seeing (though the gridlines were thinner). It was easy to miss if you weren't looking for it. I couldn't get the pattern to go away and Topaz support was of no help so I stopped using the software.

Was the original file uprezzed by your client?

[dgberg]

I will have to ask. I don’t believe so as the prints were quite small. Anyway. With the noise gone they now print perfect. Very strange indeed.

[Jeremy Roussak]

I've seen something similar in raw images taken on my Sony A7Riv at very high ISO (40,000-52,000), after the initial rendering in LR. Following denoise in LR (I've not tried Topaz), it went away. It is certainly jolly strange.

Jeremy

[Lessbones]

if getting rid of the noise fixed it then it's gotta be moire from the process of converting from the native dpi of the file to the printer's screening algorithm.  Same type of thing happens when scanning an image with a halftone screening pattern-- inkjet printers generally use FM screening to try to hide the dot pattern, but since it still exists it will once in a while cause a visual issue like this.

[Czornyj]

+1 it’s moiré from scanned halftone screening 99%

[dgberg]

Very interesting, thanks guys. Learn something new every day.