Questions on Building a simple paperback scanner

[johnwhelan]

I have a radial arm saw available and I've two Cannon A810s (16MP) on order.

What do I need to take into account?

The maximum page size I'm interested in at present is 7 inches by 4.25 inches (roughly 18 cms by 11cms).

I like the idea of an inverted V in acrylic and hanging the book over the top using gravity to flatten the page however I note that many designs do the opposite and have an V shaped either glass or acrylic that is lowered down to keep the pages flat. What are the advantages / disadvantages of each method.

Paperbacks can use quite small print so what distance should the cameras be from the page to get the best image? Some have a very narrow margin on the book binding side should this influence the thickness of the acrylic or glass?

I note also that some designs use a V shaped "clamp" that rests at the top and bottom of the page, without acrylic or glass does this give a better image?

Thanks John

[rkomar]

I'm still in the planning stage myself, but have been getting some experience taking pictures of music albums. I don't know what quality the A810 is, but my A4000 cameras are just okay in that regard. I have found that it helps to pull the camera away and use the optical zoom to get the subject framed properly. This reduces the amount of barrel-distortion that needs to be corrected in the camera. It also improved the image quality for me towards the outside of the image (less ghosting around bright areas and more even focusing across the image). I suspect that the lens is just not that great in my model. Another advantage is that the reflection of the camera on the glass should be less of a problem when the camera is further away. The disadvantage is that you get less light to the camera, so you need to keep the shutter open longer, but that's not a big deal if the cameras and book are solidly fixed in place. Keeping the shutter open for 1/15 of a second instead of 1/60 of a second is not going to slow things down appreciably compared to the time to write the image to SD card. So, maybe you should wait until your cameras arrive and then play around with the optical zoom before deciding where they should be placed.

I would also not design a scanner that couldn't take larger sized books. Sooner or later, you'll want to scan something bigger, and you'll have to build a whole new rig then.

[pablitoclavito]

I would also not design a scanner that couldn't take larger sized books. Sooner or later, you'll want to scan something bigger, and you'll have to build a whole new rig then.

I agree with that.

What is the distance between your camera and the book?
And, can you "lock" the shutter speed to 1/15 s in the camera using chdk, so all the photos are taken with that same shutter speed?
Thanks

[rkomar]

What is the distance between your camera and the book?
And, can you "lock" the shutter speed to 1/15 s in the camera using chdk, so all the photos are taken with that same shutter speed?
Thanks

If you have a Canon camera that is supported under CHDK, then the answer is yes. You can set the shutter speed, zoom, focus,... and lock the focus, among other things. You can also take RAW images, although that slows down the picture taking quite a bit (it takes about 5-7 seconds in my case). I haven't been photographing books yet, but I have been photographing my music albums, and there is dense text on many of them. I have the camera about 1m away, and use the optical zoom to fill the picture with the album cover. The camera, albums, and lights (+diffusion screens) are always in the same place, so I did some experimenting and found the best zoom, focus and exposure time settings, and put them into a script I use for taking the pictures. I found that if I let the camera determine the focus and exposure time for each picture, it often got them slightly wrong, and the results were variable. By fixing them with the script, I always get good, reproducible pictures. I'll definitely be doing the same thing when I set up the book scanner.

[pablitoclavito]

Yes, my camera has CHDK support. Until now I was only locking the focus, but in the camera menu (not in CHDK)
I will try taking the photos with the camera far away from the book as you said, and see the results.
Thank you.

[johnwhelan]

I would also not design a scanner that couldn't take larger sized books. Sooner or later, you'll want to scan something bigger, and you'll have to build a whole new rig then.

I agree with that.

What is the distance between your camera and the book?
And, can you "lock" the shutter speed to 1/15 s in the camera using chdk, so all the photos are taken with that same shutter speed?
Thanks

At 12 cms the paperback page fills the screen. I understand CHDK can control the focus, speed etc etc.

So do I design at 12 cms or think in terms of using the optical zoom and go a little further out? I have a tripod so can play if need be before cutting anything.

Thanks John

[rkomar]

If you put the camera as close as possible, then you won't be able to photograph a larger book from there. The image will also likely have some barrel distortion (at least it does on my A4000 when fully zoomed out). Personally, I would pull it back a couple of feet and use the optical zoom. If you're only shooting one page at a time, then you'll also likely need to be able to move the center of the focus for different sized books (or get a lot of wasted space in the photographs). I plan on being able to slide the cameras horizontally to move the center of focus. You can tilt the camera instead, but then you'll have to do key-stone corrections on the images, since the camera angle won't be exactly perpendicular to the pages.

[johnwhelan]

If you put the camera as close as possible, then you won't be able to photograph a larger book from there. The image will also likely have some barrel distortion (at least it does on my A4000 when fully zoomed out). Personally, I would pull it back a couple of feet and use the optical zoom. If you're only shooting one page at a time, then you'll also likely need to be able to move the center of the focus for different sized books (or get a lot of wasted space in the photographs). I plan on being able to slide the cameras horizontally to move the center of focus. You can tilt the camera instead, but then you'll have to do key-stone corrections on the images, since the camera angle won't be exactly perpendicular to the pages.

So step one is to create a dummy rig with acrylic or glass over the page then photograph it at different distances to see which gives the lowest distortion?

Thanks John

[rkomar]

So step one is to create a dummy rig with acrylic or glass over the page then photograph it at different distances to see which gives the lowest distortion?

Thanks John

That's what I would do. It will probably also show you if you're going to have problems with the camera being reflected in the glass/plastic (although that's not a serious problem if you're just going to be photographing text, since the reflection will mostly disappear when you convert the image to black and white).

I had all kinds of problems I didn't anticipate when I started photographing music LPs. Lighting (temperature and evenness), focusing, exposure,... I'm learning a lot doing that before I tackle photographing books. I think you'll find that a test rig will be worth the effort.

[johnwhelan]

How do I check the version number on an A810?

http://chdk.wikia.com/wiki/CHDK_for_Dum ... 26S_camera

Has some information but not quite enough.

I have created both ver.req and vers.req in the root of the card. There is a center button marked "func set" then a circular button marked disp at the bottom auto at the top and two symbols either side.

There is one folder present called DCIM.

Thanks John