light issues and camera settings, need help

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light issues and camera settings, need help

Postby yamanassaf » 12 May 2011, 18:48

so far I have read numerous threads, set my camera to low ISO (about 100). I used a halogen work light 500 watts. I have also tried CFL and full spectrum lights, and no matter what type of light I try there is always one problem that I can't figure out how to solve, the light does not spread equally (some areas are too dark and some areas are too bright, areas in the center are usually too bright, and light fades as you move further from the center of the page), moving the light further away from the page helped a little in reducing the glare coming from brightly lit areas as the intensity gets reduced when the light source moves away however the light is still not spreading equally. I think this will require a bit of knowledge in physics and photography. I suck at both. I was thinking of making reflectors made of aluminum foils to spread the light equally but I don't know how to start, and whether it's necessary.

Halogen light tend to produce image with a brownish background rather than the desired white background you typically get when you scan your document using a flatbed scanner. I used ABBYY OCR software and was able to get the desired white background after processing the image however OCR accuracy sucks, so I choose to keep original image and place the text behind the image, getting the desired white background is an issue as well, and yet I am not able to figure out how to fix it, does it have anything to do with camera setting? I have tried almost all settings on my camera and was not able to produce an image with a white background. is there a bright white light I could get? the maximum white light I could find in the hardware store was about 100 watts (not even close to 500 watts), I saw the halogen worklight to CFL conversion tutorial however was not sure whether it will produce a white light with 500 watt.

I took the following two images to demonstrate what I am talking about, one image shows the brownish background I am talking about, notice how the center is brightly lit and the sides are dim. The other image background got lighter as I turned on the flash however it is still not as white as I like it to be. Any help on this matter is appreciated
yamanassaf
 

Re: light issues and camera settings, need help

Postby Misty » 13 May 2011, 10:30

The uneven illumination problem is simply an issue of how you're holding your books. Uneven pages are going to get uneven lighting. If you make sure your pages are flat, it's much easier to spread light uniformly across the page. That's one of the reasons why most builds use a V-shaped platen with a light pointing down at each page; it makes it easier to get flat pages with light at the correct angle.

The colour you're getting is a result of the white balance setting on your camera. If the auto white balance doesn't produce good results, you can try the various presets to see if one is a good match for the light temperature. If not, there is probably a custom option - you're using an Elph 300, right? If you fill the camera frame with a pure white sheet of paper under the lighting conditions you're scanning in, you can use the custom white balance option to have the camera calibrate itself to the lights to get a more accurate colour rendition.
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Re: light issues and camera settings, need help

Postby yamanassaf » 13 May 2011, 20:37

thanks for help, yes I am using Elph 300, I was intending to buy an older model, the sales person said that this is newest model for a canon compact camera, and it has a high sensitivity sensor which allows it to take good pictures in poorly lit areas, so I thought this camera should be ideal for poorly lit pages. I can't attach a power cord to the camera which could be a problem in the long run, I guess I need to get two cameras for the v shaped stand, I am not sure whether I could buy a cheaper different model camera and use it along with the one I have. initially I was intending to use a single camera to take pictures of two pages at once and use ABBYY to split the image. building the v shape stand is easy however constructing the platen is a challenge, I am still not sure whether it will be made of glass or acrylic. does acrylic or glass has to have anti-glare coat ? where would I buy this stuff? I guess I need to do some homework and read more threads. anyways thanks for help
yamanassaf
 

Re: light issues and camera settings, need help

Postby Misty » 16 May 2011, 11:12

High sensitivity sensors are really more appropriate for photography than for book scanning, so I don't think that's necessarily a criterion to judge cameras by. I typically recommend that users try to keep their sensitivity near the low end of the camera's range, since the higher the setting the more noise that is introduced into the image and the lower fidelity and sharpness of the image. Those grainier images are likely to produce lower-quality Scan Tailor and OCR results, though I haven't experimented to determine whether there's a range above the camera's minimum ISO that is safe to use without harming results. If you're scanning illustrations, rather than pure text, I definitely don't recommend going above the base ISO, but it looks like your books are pretty much all text.

I've actually had reasonably good luck with a V stand and no glass at all, so if you're not confident in your ability to do make a platen you may want to give that a try. Search the forum for "air platen" for glass-free solutions. I haven't experimented much with building platens, but there are many good threads around.
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