Thanks.

The lighting is actually really simple. First of all, you have to get the luminance way up. Hence, halogen bulbs. They do a decent job of diffusing across the page.

But you’re right, the output pages have serious non-uniformities. So join me in math land for minute. What we want to do is remove the non-uniformities due to light, not to text. So we simply take a picture of a blank page in the book (one for each side), invert it, and add it to the original. Inverting and adding it is the equivalent of subtracting the effects of luminance. You can do this in Photoshop using the “linear dodge (add)” layer mode. That is all the processing we currently do, though we (Aaron and I) have some ideas for smart thresholding that will really reduce noise in the output.

I think they’re 75 watt bulbs? Don’t have them in front of me. Any high-output halogens will do, as long as they have that bubbly lens surface. The key here is very high output.

Acrylic does have a slightly lower refractive index than glass (1.49 vs 1.5 and up) but I don’t think this is significant. The big problem with acrylic is that it is hard to clean without scratching. I chose it primarily because it is so easy to fabricate with. I’m now working with another Instructables method on some different platen designs involving glass.

For instance, how did you get the scan from the demo book so evenly lit? The page images in the screen shot above clearly have light and dark zones. Do you perform some kind of regional lightening/darkening in the software stage?

What’s the wattage of the lamps you use?

I use a glass platen (I use a single camera set-up, so don’t need a glued together wedge), which was very cheap to get: just buy a 1-dollar picture frame, and you don’t just get a sheet of glass, but also a piece of cardboard that helps to prevent breakage when you are not using it.

I can imagine that plexiglas is safer because of the way it breaks. What are its reflexive properties though? I also understand that plexiglas lets slightly more light through than glass.

I am going to attempt a simplified version this summer.

I’m proud to say the project got a mention on archive.org — my heroes.

http://www.archive.org/about/faqs.php#Texts_and_Books

And that software looks especially slick [nods to Aaron].

To the dumpsters!