Scanning table for old digital cameras

I have several sheetfed scanners. They are great in many ways — though not nearly as automatic as they could be — but they are expensive and have their limitations when it comes to real-world documents, which are often not in pristine shape.

I still believe in sheetfed scanners for the home, in fact one of my first blog posts here was about the paperless home, and some products are now on the market similar to this design, though none have the concept I really wanted — a battery powered scanner which simply scans to flash cards, and you take the flash card to a computer later for processing.

My multi-page document scanners will do a whole document, but they sometimes mis-feed. My single-page sheetfed scanner isn’t as fast or fancy but it’s still faster than using a flatbed because the act of putting the paper in the scanner is the act of scanning. There is no “open the top, remove old document, put in new one, lower top, push scan button” process.

Here’s a design that might be cheap and just what a house needs to get rid of its documents. It begins with a table which has an arm coming out from one side which has a tripod screw to hold a digital camera. Also running up the arm is a USB cable to the camera. Also on the arm, at enough of an angle to avoid glare and reflections are lighting, either white LED or CCFL tubes.

In the bed of the table is a capacitive sensor able to tell if your hand is near the table, as well as a simple photosensor to tell if there is a document on the table. All of this plugs into a laptop for control.

You slap a document on the table. As soon as you draw your hand away, the light flashes and the camera takes a picture. Then go and replace or flip the document and it happens again. No need to push a button, the removal of your hand with a document in place causes the photo. A button will be present to say “take it again” or “erase that” but you should not need to push it much. The light should be bright enough so the camera can shoot fairly stopped down, allowing a sharp image with good depth of field. The light might be on all the time in the single-sided version.

The camera can’t be any camera, alas, but many older cameras in the 6MP range would get about 300dpi colour from a typical letter sized page, which is quite fine. Key is that the camera has macro mode (or can otherwise focus close) and can be made to shoot over USB. An infrared LED could also be used to trigger many consumer cameras. Another plus is manual focus. It would be nice if the camera can just be locked in focus at the right distance, as that means much faster shooting for typical consumer digital cameras. And ideally all this (macro mode, manual focus) can all be set by USB control and thus be done under the control of the computer.

Of course, 3-D objects can also be shot in this way, though they might get glare from the lights if they have surfaces at the wrong angles. A fancier box would put the lights behind cloth diffusers, making things bulkier, though it can all pack down pretty small. In fact, since the arm can be designed to be easily removed, the whole thing can pack down into a very small box. A sheet of plexi would be available to flatten crumpled papers, though with good depth of field, this might not strictly be necessary.

One nice option might be a table filled with holes and a small suction pump. This would hold paper flat to the table. It would also make it easy to determine when paper is on the table. It would not help stacks of paper much but could be turned off, of course.

A fancier and bulkier version would have legs and support a 2nd camera below the table, which would now be a transparent piece of plexiglass. Double sided shots could then be taken, though in this case the lights would have to be turned off on the other side when shooting, and a darkened room or shade around the bottom and part of the top would be a good idea, to avoid bleed through the page. Suction might not be such a good idea here. The software should figure if the other side is blank and discard or highly compress that image. Of course the software must also crop images to size, and straighten rectangular items.

There are other options besides the capacitive hand sensor. These include a button, of course, a simple voice command detector, and clever use of the preview video mode that many digital cameras now have over USB. (ie. the computer can look through the camera and see when the document is in place and the hand is removed.) This approach would also allow gesture commands, little hand signals to indicate if the document is single sided, or B&W, or needs other special treatment.

The goal however, is a table where you can just slap pages down, move your hand away slightly and then slap down another. For stacks of documents one could even put down the whole stack and take pages off one at a time though this would surely bump the stack a bit requiring a bit of cleverness in straightening and cropping. Many people would find they could do this as fast as some of the faster professional document scanners, and with no errors on imperfect pages. The scans would not be as good as true scanner output, but good enough for many purposes.

In fact, digital camera photography’s speed (and ability to handle 3-D objects) led both Google Books and the Internet Archive to use it for their book scanning projects. This was of course primarily because they were unwilling to destroy books. Google came up with the idea of using a laser rangefinder to map the shape of the curved book page to correct any distortions in it. While this could be done here it is probably overkill.

One nice bonus here is that it’s very easy to design this to handle large documents, and even to be adjustable to handle both small and large documents. Normally scanners wide enough for large items are very expensive.