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Old 09-22-2007, 03:39 PM   #13
ereszet
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In search of perfection - lighting

Before photoscanning hundreds of pages, it is worth making sure that the lighting is uniform. Neither your visual inspection of the original paper document nor the camera LCD display or the computer screen (if you shoot from a camera connected to a computer) are good enough to see the bright and shadow areas due to non-uniform lighting (unless shadows and bright spots are very discernible).

There is a commercial program (Psremote) that in its preview mode can highlight the areas that are too bright according to a selected level of luminosity. However its use is limited to cameras that can shoot from the computer and it can only show which areas are too bright at a chosen threshold rather then areas with different levels of brightness.

I deviced a method which is simple and effective to check the lighting uniformity before shooting hundreds of photos.

You just take a test photo as jpg and compress it aggresively using Irfanview or any other similar progam. On the compression scale of 100 (best quality) to 1 (lowest quality) you may choose 10 or lower quality. The resulting compressed jpg will show "clouds" or areas that are similar for the sake of compression. For our purpose, it shows areas of pixels with similar luminosiity. By forcing a very low quality, we can see "clouds" even in a photo that is otherwise almost perfect. Once we know which parts of the test photo are under- or overlighted we can: move the cradle, move the lamp, use a curtain or a black bristol paper to block the light from reaching the original at various points and angles.

The attached pictures show:
Daylight.jpg - a test photo taken in the middle of the room with two windows and various objects in the way of light (the gray line along the photo image is the feature of the original paper page).
Daylight10.jpg - same photo compressed at the level of 10, showing the clouds of non-uniform brightness
DayTungsten.jpg - like daylight.jpg but with a ceiling and overhead lamps switched on (I do not recommend this setup, but I have no way to stop sunlight during the daytime - blinds are too transparent. Usually i shoot at night.
DayTungsten10.jpg - same photo compressed at the level of 10

You wll notice that the better quality DayTungsten.jpg shows some non-uniformity. It is due first of all to the sunlight but also to the fact that upper part of v-cadle panel is closer to the overhead lamp than the lower part of the panel. That is why I recommend using a bright ceiling lamp only. At at distance of 1.5 or 2 meters (depending on how high is your ceiling), the 20 centimeters between the upper and lower part of the cradle panels make little difference. You can also put a white paper (you can experiment with its dimensions) on the panel opposing the original page, and it will act as a kind of mirror, directing more light to the lower parts of the original. One method of achievieng quite uniform light is using the camera flash directed to ceiling. The light reflected from the ceiling is more dissipated. I even experimented with double reflection, i.e. flash directed to --> a sheet of bristol paper (or a sheet of matt aluminium) --> ceiling --> v-cradle.

If you are a little ovewhelmed with all this, remember that one ceiling lamp will usually be ok. The brighter is the lamp, the easier it is to get the white balance (i.e. to make the white pages white rather than gray, yellowish or pinky, while keeping the print black) in the processing afterwards. I am not going into RAW processing, white balance/ISO/camera setting problems or commercial heavy weight and costly software to process your photos. I concentrate on fast shooting and batch processing. But if you plan to convert all your family photos to digital ones, you may want to learn about RAW image format and all the tricks of professional photographers. There is abundance of advice on that on the internet but rather little of what I give you here in terms of convenient fast practical arrangements.

Please note that the paper originals were put under the glass but the photos show no reflections thanks to my v-cradle design. Better results can be achieved with proper lighting, zoom, and processing (see Tungsten processed.jpg).

The question is: do we need to make the lighting perfectly uniform? My answer is:
yes, when we deal with color originals;
rather yes, when we deal with gray photos;
not necessarily when we convert the pictures to mono.

Unless you are a perfectionist and the original is in blue dark, my setup is very forgiving even with bad lighting.

BTW. There are some commercial programs that can process the photos and help you make the lighting more uniform, but in my opinion they require fine tuning for each and every photo individually. A proper test and light setting before taking pictures is the only way to avoid disappointment in the final stage of book processing.
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