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

Camera Alignment

Everything camera related. Includes triggers, batteries, power supplies, flatbeds and sheet-feeding scanners, too.
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univurshul
Posts: 496
Joined: 04 Mar 2014, 00:53

Camera Alignment

Post by univurshul » 24 Apr 2010, 03:09

...So I was reading briefly into issues on other posts regarding right and left cameras creating larger/smaller text on adjacent pages.

1. I noticed that on some early scanner builds the camera post placement was "eyed". I'm guessing the process is different for many, but I found the centerline of the lens on my cameras to the centerline of their mounting bolts, where I offset the mounting location on the baseboard of the scanner in relation to the center line of the book holder. This makes makes sense to me, but it was more like an educated guess to install the camera posts this way. Coming from someone who doesn't use or know much about cameras beyond an iPhone, I think it's going to work for optimally for the size of the platen, holder, hinge assembly, etc.

2. The issue with zooming in on the book to setup capture (which could create larger and smaller text every other page): What I think I'm going to do is create identical camera post angles and identical distances from the surface of the platen to the surface of each camera lens. Then the issue of a final zoom to get the "goods": not sure, but I'm hoping there's a data reference on an A590 IS that references you what the zoom reading is? Or is this done on 'feel', and digitally process later to average the text & page sizes to match? Any ideas for the Mac user, let me know.

Thanks again. Should have my pictures of the scanner submitted by next week. Where would I post pics?

univurshul
Posts: 496
Joined: 04 Mar 2014, 00:53

Re: Camera Alignment

Post by univurshul » 24 Apr 2010, 03:11

--Pardon my butchered English writing at 1:30 am. Regards.

univurshul
Posts: 496
Joined: 04 Mar 2014, 00:53

Re: Camera Alignment

Post by univurshul » 24 Apr 2010, 03:25

--wait: #2 above would be an issue because the book holder slides and moves from its origin as you scan through a thick book. Hmmm, not sure if I just answered my own question, but it sounds like software is the ideal treatment for default-sizing pages and text....

spamsickle
Posts: 596
Joined: 06 Jun 2009, 23:57

Re: Camera Alignment

Post by spamsickle » 29 Apr 2010, 08:17

You may be referring to one of my posts. I recently scanned a book for someone else, which made me more aware of potential quality concerns that I've tended to ignore when scanning for myself, and this zoom issue was one of them.

On my scanner, the camera mounts can be adjusted from side to side, but not up and down. That means potential keystoning, but I live with it.

Once I have the cameras positioned, I use the zoom feature on the camera to fill the frame. I'm eyeballing this using the LCD display on the camera, and I've discovered that even when the images look the same on my postage-stamp display, they may still vary by up to 10% when I examine the resulting JPEGs.

The last time I looked at CHDK, there was an option to zoom in or zoom out, but not an option to set the zoom to a specific value. I assume it would be possible to write your own routine to set a specific zoom value by having the CHDK script zoom in or out some number of times greater than the maximum range for the camera, and then zoom out or in for the number of times that represents the value you want. I haven't considered implementing this myself, because my cameras don't talk to each other, and I'd have to settle for a canned value rather than basing the zoom on the size of the book I'm scanning. I guess different scripts for different book sizes would be one option, but as I say, I haven't bothered to try to implement this to see if it will even work.

I think it makes more sense to reconcile the image sizes after scanning, by adjusting the DPI values. Currently, though, Scan Tailor doesn't allow different DPI values for right and left images (there is no "apply to every other image" in the DPI setting). Using Scan Tailor alone would thus mean processing left and right images separately, and merging them after the Scan Tailor processing. Doing that would make it more difficult to get the final left and right page sizes (the size of the page after Scan Tailor's "soft" and "hard" margins are added) to be the same, though it could probably be done. The difficulty would arise if you ever had to manually select content for a page, since Scan Tailor adds its margins to that selection. Almost every book I scan requires manual selection for some pages.

Alternatively, you could pre-process the files with something like ImageMagick to make the left and right page images a uniform size, then merge them and process them with Scan Tailor. I think that's probably the best approach for now, until such time as Scan Tailor offers different DPI adjustments for left and right images.

Practically, though, I don't really notice different sizes in the final output if I don't concern myself with making the image sizes match, so I'm currently taking the lazy way out and ignoring the whole issue. Scan Tailor makes the pages a uniform size, and the slight difference in size of the content within those pages is, to me, no more perceptible in the final PDF than it was on the tiny viewfinder when I was shooting.

Sorry to be so focused on software in the hardware section...

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