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Digital Cameras vs Scanners for OCR?
ttennebkram asks: "With 6 and 8 Megapixel cameras on the market, some now with Wifi built in, it might be more convenient to shoot pictures of your bills and papers with a camera than fussing with the scanner. By the numbers, it would seem feasible. 300dpi for an 8.5"x11" sheet of paper works out to about 8 megapixels; 300 dpi is usually what OCR vendors suggest. I imagine for high volume good results you'd want to maybe mount the camera on a tripod arm over your desk. Heck, I was thinking of a glass desk and maybe one camera below and one above, and maybe a foot pedal to trigger the cameras (and I suppose a flash and high F-stop would help as well). If I could quickly 'snap' all the junk paper I have and electronically file it, maybe OCR the images at night in batch while I'm asleep, and then maybe get rid of all that paper once and for all. Using a traditional cheap scanner just takes too long. So has anybody tried this? I realize that camera optics are different than scanner optics, so maybe it's not just a question of raw pixel counts. Any thoughts?"
...the aspect ratio and even lighting are your enemies. It's almost impossible to shoot a bill or a check stub dead on, at close rage, without fish-eye'ing, and without getting in your own shadow. Sure, you might have a little white linnen box that you use to take your eBay photos, but, seriously, this is a job for a scanner.
I have some experience doing what you're trying to do. I've even done this type of work in professional labs with serious pro equipment (it was my job). It's a huge pain in the butt.
I'm currently digitizing my collection of old tabloid punk magazines from the 1970s. I had to use a digital camera because flatbed scanners that do 11x17 or larger are extremely expensive, they're like $3000 or more. So I did some experiments with my consumer-grade 5 megapixel digital camera. The results were adequate, barely (and I have an art degree in Photography, this stuff is easy for me, YMMV). I've currently suspended my project until I can afford a higher rez digital camera, mostly because 5Mp is barely enough to capture the little 6 point type that is used in large sections of the magazines. But let me tell you more generally what I've learned.
First off, you'll need a copy stand. This is a fairly standard photo accessory, but a good copy stand is fairly expensive. You need something that is easily adjustable, so you can raise and lower the camera to get the document to fill the frame, without using too much zooming. The copy stand keeps the camera parallel to the target at all distances. It is important to have quick adjustability in height, rather than zooming. You'd be much better off using a "prime lens" rather than a zoom, as zooms tend to have barrel and keystone distortion.
Secondly, you need lights. If you only want to copy written documents (or B&W magazines like me) you can use cheap spotlights. If you want to do color, you need much better lighting, something with a fixed color temperature, or a flash system. Spotlights are really hot, and when I work in my small office, it gets intolerably hot when I spend about an hour photographing. For better, more repeatable results, you'd be better off getting a flash system. BUT...
Here is the sticking point. You need something to keep the documents flat. That means placing them under a sheet of glass. So you are going to get reflections from the lights, and flash is high intensity lighting which makes it even more difficult to control reflections. The usual method is to put polarizing filters over the lights and the lens, to cancel out the reflections. This is a rather complex method, and a LOW END professional copystand with polarized lighting will set you back about $2500.
OK, so what I did is I adapted my old disused photo enlarger. It was a huge monster for 4x5 negatives, I took off the enlarger head, and used a Bogen photo clamp with a ball-head joint attached to the motorized arm that goes up and down. It does a fairly good job as an improvised copy stand, but it is pretty cramped, the baseboard is only designed to make max 20x24 prints. Also it is a HUGE pain in the ass getting the camera leveled with the baseboard, I use a bubble level. Then I attached a cheap set of tungsten photofloods to the wings of the enlarger, so the light hits the baseboard at a 45 degree angle, to reduce glare. Note that it is best to point each light at the far side of the document, so the light paths cross each other. This gives the light a little distance to fan out and eliminate hot spots. I don't put my documents under glass, they're newspaper pages, so I flatten them for several weeks (!!!) under weights, then if there's a little curl, I use weights (like heavy metal rulers) at the edges, or hold the edges down with post-it notes. That eliminates the need for a glass plate to hold them down, and I don't have to deal with reflections. However, it takes a LOT of time and effort to get the documents positioned and flattened correctly, it is not a quick process.
I use a Canon camera, so I use the Canon Camera Remote to my laptop to preview and take the shot. Even with the lights and some fill flash, I can end up with exposures of 1 or 2 seconds, so I can use a narrow f-stop. This shouldn't be necessary for a flat object, which requires no depth of field, but I find that the lens is sharper stopped down. It takes quite a bit of fiddling to get the optimal