What is Descreen in the scanner software?

What is Descreen? I found this option in the scanner software. What if i select Descreen? How the photo will be scanned if i select "Descreen" and "NoDescreen"? Which one should I use while scanning the photo? either "Descreen" or "NoDescree"?

Please help me.
I think it has to do with reducing or removing moire pattern.
If you scan in a photo from magazine using a high dpi, you should see moire pattern. You know, funny little offset pattern of colours from the printing process.

I think that's what it is.
Yes, exactly, but some prefer scanning offset printed pictures at an angle, and with a very high resolution, then downscale in Photoshop.

The best is to do test to see which operation is the most powerful!

If you are scanning Photos (not magazines) you do NOT need to use descreen.

Remember that pictures from magazines are copyrighted and that you cannot legally re-use them without the approval of the copyright holder(s)
ThanX for your replies and i got how Descreen Works.

ThanX "Welles" for suggesting a great site on "Scanning tips".

ThanX Stroker and Spectre...

With Regards,

Just a heads-up, I tried scanning and saving as
PDF - text over image and
PDF - image over text.

I'm scanning in sheet music from a playbook so that I can reprint and place the prints in plastic page protectors in a 3 ring binder, thus saving my original songbook, which will otherwise be ripped to shreds by an accompanist during performance.

When I tried PDF - text over image, the guitar chords turned into big black dots. They were perfectly shaped, but hardly what I needed.

When I tried PDF - image over text, the guitar chords were rendered perfectly.
kz :)