Page lighting, exposure, etc.

[JDSimmons]

I've scanned a few books with the methods described on this site and I find that my page images are not the same color as the actual paper of the page. I'm using a single desk lamp with a 100 Watt bulb for lighting and the "Tungsten" setting for white balance. The pages are coming out grayish when the actual pages are a very light cream color. I think I'm getting plenty of light on the pages, but my camera's exposure settings aren't right. Now some of the pages I've photographed that have color illustrations look quite good. It just seems to be the text/grayscale illustration pages that come out dark. To see an example of what I'm talking about check these links:

http://www.archive.org/details/AncientM ... ierreLouys

http://www.archive.org/details/OrpheusMythsOfTheWorld

To see an example of a page with a color image that looks good check this out:

http://en.flossmanuals.net/floss/publis ... eskew3.jpg

Suggestions?

[JDSimmons]

To see an example of a page with a color image that looks good check this out:

http://en.flossmanuals.net/floss/publis ... eskew3.jpg

Actually the page color on this one looks dark too. The picture looks about right, but the page color should be lighter and more cream colored.

[Tim]

Yeah, same situation here and I think the only solution is more light. You can adjust the exposure setting(s) on your camera to increase the exposure, but at some point you are going to wash out the color and/or text. You can certainly see an improvement in color quality and contrast of a page for each additional light bulb added. What I don't understand is why so much light is needed. When I take a picture with a white door in it, it looks white, so why does a picture of a page look grayish unless I put 3000 watts of light on it? I'm curious how a high powered professional flash with a diffuser on it would work out.

[Misty]

A few things:

- The problem with colour is colour balance mainly, not exposure. The "Tungsten" setting doesn't necessarily guarantee that it has the exact white balance of your lights. Are you using a Kodak CX7525? Unfortunately it looks like your camera doesn't support recording a custom white balance, which is going to limit your ability to get the colour right. Experiment with the different settings to see if you can get something better. You may need to apply white balance in post-processing. What OS are you using? I can look into options for fixing up your JPEGs. What you would be looking to do is shoot a pure white (not off-white!) piece of paper filling the image, using the Tungsten or another non-auto white balance, and use that to determine the colour corrections needed. That would then be batched in post-processing across all your images.

- It looks like your camera doesn't have a non-auto mode, and I think that's part of the problem. As far as your camera can tell, pages with text and pages with images are different brightnesses from each other and so it's likely using different exposure settings for them. That is going to limit how much you can do about that.

That said, it also looks like your exposure compensation levels are too low and all of your images are being exposed too dark. You need to increase the exposure to make the page images brighter and slow the shutter speed down a bit.

Edit: Like I showed Ann before, I'm going to show you the histogram of the image to show you what I mean about underexposure.

arabian-histogram.png (8.55 KiB) Viewed 2057 times

Do you see how the vertical lines are in the middle, surrounded by an empty area to either side? That's usually an indication of underexposure. In this case, upping the exposure wouldn't wash it out, it would make the image look more like it does in real life.

As for the white balance:

ArabianNightsDeskew3-wb.jpg (162.33 KiB) Viewed 2057 times

Without seeing it in real life I can't say for sure, but the original book probably looks a little more like this, right? I tweaked the white balance and increased the software exposure compensation to simulate what it would have looked like with a higher exposure.

Edit 2: It looks like the paper colour is different for your left and right pages. Are you shooting them with the same lights? Both of them are too blue (which is a sign of wrong white balance), but to different degrees.

papercolour.jpg (104.06 KiB) Viewed 2057 times

[JDSimmons]

A few things:

- The problem with colour is colour balance mainly, not exposure. The "Tungsten" setting doesn't necessarily guarantee that it has the exact white balance of your lights. Are you using a Kodak CX7525? Unfortunately it looks like your camera doesn't support recording a custom white balance, which is going to limit your ability to get the colour right. Experiment with the different settings to see if you can get something better. You may need to apply white balance in post-processing. What OS are you using? I can look into options for fixing up your JPEGs. What you would be looking to do is shoot a pure white (not off-white!) piece of paper filling the image, using the Tungsten or another non-auto white balance, and use that to determine the colour corrections needed. That would then be batched in post-processing across all your images.

I am using a Kodak, possibly a CX7525. The name sounds about right. It's a 5 megapixel camera. This morning I noticed an exposure compensation setting which I might try some test shots with.

My OS of choice is Linux, but I'll use XP if I have to. I am familiar with The GIMP and Image Magick, so if you can suggest how to use those tools (or any others) to correct this in software I'd be grateful. Your corrected Arabian Nights page looks good.

I'm working on a FLOSS Manual on e-books and I'm trying to come up with best practices for creating all kinds of e-books. You can check out what I've written here:

http://en.flossmanuals.net/ReadingandSugar/Introduction

Any feedback, etc. you could provide would be great.

James Simmons

[translucent1]

Have you tried setting the exposure compensation on your camera to some positive value? I'd try +1EV to start.

Also, since you're running linux, you can use imagemagick to batch adjust levels in your images:

$ for i in `ls *.JPG`; do convert $i -level 20%,80% adjusted_$i; done

Where 20% and 80% will set the black and white points repectively. Experiment with different values until you get output that you like.

[JDSimmons]

The suggestion to put more light on the page seemed to be the most useful. When I tried to use Exposure Compensation it just washed out the middle of the page, where my single overhead light shone brightest (and where my camera used as a reference point for exposure). I bought a couple of clip-on desk lamps and have them shining on the book from either side, making the page lighting more even. This seems to have helped.

[univurshul]

One hardware culprit is CFL bulbs. These buggers could be pulled from the same box and they'll cascade a rainbow of color all over your media throughout a scan.

Consider using high wattage incandescents (via Tungsten balance) for rich-color reproduction and cheap CFLs for black and white processing on Scan Tailor. LEDs could even mess with your color as well; it depends on the brand and the weight of the gold in your pocket.

Scan Tailor does some really impressive color processing as well--so as long as your lights and cameras settings are identical, assuming your exposure settings are capturing accurate depth, I think your post-processed images will be awesome.

Post your results from testing when you have time.--Regards.

[JDSimmons]

Actually I don't use CFL bulbs. I use incandescent bulbs and the "Tungsten" white balance setting on the camera. We use CFL bulbs all over the house, but the warnings on this site against them were already pretty clear.

[univurshul]

Actually I don't use CFL bulbs. I use incandescent bulbs and the "Tungsten" white balance setting on the camera. We use CFL bulbs all over the house, but the warnings on this site against them were already pretty clear.

Exactly...But CFLs are used in so many homes, they're abundant and I see no reason not to put them to work whenever possible. They have obvious trade-offs considering their toxicity in manufacturing to their power draw/life cycle. But like I said, for bulk text-body scans, CFLs will save your incandescents' life; it makes no difference when you process a book to 8 bit black and white binary & grayscale. The color tint won't exist at that point. For example, look at the 2 images and tell me which one used the CFLs:

1.jpg (148.28 KiB) Viewed 1969 times

2.jpg (142.71 KiB) Viewed 1969 times

Saves you $$$ on the electric bill. The full color images are understandably a different animal