avoid stochastic printing stripes?
donovan1 (59 pencils) | Fri, 2012-05-18 09:25after ripping an image in stochastic mode our large banner printer creates unwanted horizontal moire stripes (the stripes have less ink coverage, therefore appear as bright stripes). the stripes normaly occur on color surfaces that constist of two inks like for example cyan+yellow.
how would you solve this issue, to print the colors without the bright moire stripes?
Commenting on this Forum topic will be automatically closed on July 13, 2012.
I assume you mean stripes made in direction of print head stroke? Typically calibrating the printer for paper length solves this issue. You'll want to find the controls/test that your printer is printing X feet and that matches the number of feet you are outputting.
When the 'reality' is different than the 'expected' value, you'll see stripes in the output.
Without my sense of direction, I don't know where I'd be.
Yes, the bright stripes occur in direction of print head stroke. Actualy, we print the banners on PVC.
I'm using Onyx for ripping. For some reason, the printer always prints the banners a few centimeters shorter than the original file dimensions, therefore I scale the banner dimensions in the Onyx "Size" tab to a factor of 1,0028. Thus the final rips are scaled a bit, which maybe affects the stochastic pattern and creates linear Moire. You can see this effect for example in Photoshop when trying to zoom out a stochastic image.
However the final separation TIFs that are sent to the printer are regular stochastic images without Moire.
Is it banding that you're referring to when you say moiré strips? If so, your color change from one end to the other may be too great, which sometimes causes this. I'm not sure about how you are printing this, but I would check your screen angles and line screen as well. Make sure everything in the tiffs is output at the same line screen (moirés can occur if using two linescreens over eachother) and that the color angles are offset from eachother (being on the same angle can cause a moiré). Lastly, your printing device could cause it. I have seen this before on flexo printers before. We have gotten a moiré on the cyan at 22.5° because the annilox were at an angle that made it show up.
Lastly, the best way to trouble shoot is to turn on each color at a time and ensure that it is not showing up on just one of the colors (I'd try the cyan as you probably won't see it in the yellow). If it's showing on just the cyan, try changing the screen angle. Otherwise, your gradation may have too great of a contrast for the length of the gradation.
Let me know more about your printing process. The banding issue now that I've re-read it could most definitely be from a blanket issue / roller hop on the printing end.