Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

Edge lighting

All about lighting. LED, CFL, Halogen, Other? Questions and info about lighting go here.
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liklev
Posts: 4
Joined: 14 Sep 2015, 09:12
E-book readers owned: mobi, adobe de, kindle on android,moon reader
Number of books owned: 1000
Country: hungary

Edge lighting

Post by liklev » 14 Sep 2015, 09:49

Hi Everybody,
I'm newbie. As mentioned in topic subject have an idea about lighting the document platen.
Unfortunately my workshop is in ruins (boxed up to move), so i can't carry out experiments.

What if the underside of a Plexiglas platen is evenly fine sanded and LED edge lighting applied in to the platen.
The diffused light should escape to the document then reflect back to the cams.

This comes from I used Plexiglas board as daily data collection sheet.
I enclosed the hard-copy sheet (data form) in a plexiglas envelope and i sanded the top sheet thoroughly.
The printed page below was clearly visible through the sanded plexi sheet.
On the sanded side i fill up the form with a pencil (graphite), then, after writing in the log i could erase the pencil marks and reuse the form.
(The classic mechanical pen tablet, but waterproof and minus 20/30 celsius no problem for pencil flow)

Happy experimenting

rkomar
Posts: 86
Joined: 12 May 2013, 16:36
E-book readers owned: PRS-505, PocketBook 902, PRS-T1, PocketBook 623, PocketBook 840
Number of books owned: 3000
Country: Canada

Re: Edge lighting

Post by rkomar » 14 Sep 2015, 14:49

The problem is that the camera is much more sensitive to light levels than the human eye, and will pick up differences in light intensity over the page. That may not be too bad if you only convert to black and white images, but grayscale and colour images will look uneven.

Similar technology is used to light up E-Ink readers, but there they have applied very high tech reflection patterns to make the lighting more even. The E-Ink front lighting is also meant for human eyes. I suspect that it would look worse when photographed.

So, I think you should expect that this will be a challenging project to get right.

duerig
Posts: 371
Joined: 01 Jun 2014, 17:04
Number of books owned: 1000
Country: United States of America

Re: Edge lighting

Post by duerig » 14 Sep 2015, 14:53

There was a similar idea proposed using a 'wedge light' here: http://www.diybookscanner.org/forum/vie ... =16&t=3034

This may work, but the two things to be sure of are (a) make sure it is bright enough so that the camera can use the lowest ISO setting (avoid graininess) and a fast shutter speed (avoid vibration blur). And (b) check to see how even the light actually is in an image. Something may look evenly lit to the eye, but still have a darkness gradient when you take a photo of it.

Hopefully you can run some experiments after your move and let us know the results.

Some scanner designs (like the Book Liberator) have cameras that are very close to the platen. But while they have many benefits (low cost, portable), they struggle with lighting. If they could be modified with edge lighting to provide even illumination, that would be pretty awesome. There is no way I could carry an Archivist up to a library to scan a book. But a new scanner like the Book Liberator with edge lighting might be perfect for that task.

-D

liklev
Posts: 4
Joined: 14 Sep 2015, 09:12
E-book readers owned: mobi, adobe de, kindle on android,moon reader
Number of books owned: 1000
Country: hungary

Re: Edge lighting

Post by liklev » 20 Sep 2015, 15:02

thanx,
good you remind me of "unevency", i can recall on LED TVs them makers also suffer this phenomenon and requires some pixel by pixel calibration for proper color rendering.

on the other hand i still would give a try sandpaper-ing the topside of platen to diffuse the light from above (mean a standard design of light from top - to eliminate reflections)
(or both side of platen)

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