Design & Publishing Center . / . Photoshop . / . Tips & Tricks


Tip #115

[Scanning without moire? 
>>Ayhan Yilmaz
>>Re: How ?
>>
>>I manage to reduce  (if not completely to an - i think - acceptable level)
>>following  your advice. Thank you. I will be waiting for your article.
>>best regards  Ayhan
>>
>>Could you please advise me  ?
>>How can I remove or reduce the chicken-net pattern (moire??) on photos
>>(scanned). If it is not possible how can avoid during scanning ?


Most scanner software has an option to DESCREEN while scanning. This should appear as a pull-down menu with selections like Magazine, Artwork, Newspaper etc.. That's because these typical types of reprint processes have typical line screen frequencies. ie.. magazines are typically screened at 133 lpi (lines per inch), newspaper is usually 65 to 80 lpi etc. These line screen frequencies also have typical angles at which they are set, off of 90 degrees, so that when the screens overlap, they don't create a moire or patterning. When you scan your artwork square to the scanner bed you typically create an alignment with an angle which already exists in the printed piece. The scanner software DESCREEN will make interpolations during the scan process to minimize the duplication of this angle. If your scanner does not have this option you can try scanning your artwork tilted at an angle. This may be enough to hit an angle which none of the colors were screened at previously. You will then have to rotate your file back to square in a pixel editing program..like Photoshop.

To get your artwork back to perfectly square, try this... Drag down a guide and align it with the bottom most corner of your file. Then, using the Ruler Tool drag from the point where your file and the guide converge directly along the bottom edge of the file. You will see in the Info Palette the angle of your line. An added benefit of PS 5.0 is that when you go to Edit> Transform > Numeric, that same angle is already preset in the rotation box. If you're using PS 4.0 or earlier, use the Line Tool, set to zero pixels and follow the above procedure. You'll have to make a notation of the angle and then do the Numeric Rotation Transform.

A couple of other tricks are to try a small amount of Gaussian Blur and Add Noise to the file. When moire is slight, this can work fairly well. But remember, you're still softening the focus and making the file noisy. These are destructive processes. The best idea is to rescan. One other item to watch out for is that some images seem to appear to have a moire on the monitor at a certain magnification but when you zoom in or out it will go away. This is purely a monitor anomaly and will not appear when you print the file.

Good luck!
Joe

Hey... thank you very much, Joe! Don't forget folks, if you do a lot of re-scanning, then the real solution is to pick up David Blatner's latest "Real World Scanning and Halftones". That twenty bucks will save you countless hundreds in agrivation in the months to come!

Joseph Kling is pre-press specialist, photoshop photo retouch expert, and generous contributor to the content of Photoshop Tips & Tricks!
see: Joe's Photo Retouching Seminar!

Back to Tips & Tricks index . / . Letters@ Department
Design & Publishing Center . / . Photoshop


Got a tip?
Send your tips... Don't forget: this is a reader-driven web site. If you use Photoshop (trademark for Adobe Systems Inc.) then ask your questions... send us your tips and tricks.

Thank you for visiting The Photoshop Wing of The Design & Publishing Center , http://www.graphic-design.com/Photoshop/Tips/
Copyright 1992, '93, '94, '95, '96, and '97The Design & Publishing Center, all rights reserved.
Contact The Design Center design team for web page critique, makeover clinics, or website design, production and hosting.