Mike Spurgeon wrote:
PZ wrote:Anyone know if a duplex scanner, which scans both sides, scans the same part of a page simultaneously? Meaning, is the light being shone on the same spot on the page on the front and back side? This should theoretically eliminate bleed through, right?Increase it. Hold a page up against a window if you need an illustration...
Right. Bleedthrough is a result of light being transmitted through the paper, so it needs to be dark on the "back" side while scanning the front. This is what a flat black "backing sheet" accomplishes, by absorbing the scanning light that is transmitted from the front of the page through the paper (which would otherwise be reflected back through the paper, modulated by the printing on the back side). All the "standard" duplex scanners pass the page through twice, turning it over in between. One of the book scanners on YouTube scans two *facing* pages simultaneously, one on each side of the scanner "probe", but it avoids significant scanning light reflection by scanning the pages in "free space", out of contact with any backing. -michael ******** Note new website URL ******** NadaNet and AppleCrate II for Apple II parallel computing! Home page: http://home.comcast.net/~mjmahon/ "The wastebasket is our most important design tool--and it's seriously underused."