Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

Can the lights be too bright?

All about lighting. LED, CFL, Halogen, Other? Questions and info about lighting go here.
bsbob
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Can the lights be too bright?

Post by bsbob » 22 Apr 2014, 19:15

Is it possible to use too many lights?

Assuming the lights are positioned so there's no glare/reflection on the platen.

And assuming there isn't a huge of amount of heat generated.

If you have a choice between 1, 2, 4, etc. lights.... What's the best way to go? Are two floodlights better than one? Are four even better?


Same thing for watts... 10W? 20? 30W? Is it just wasting electricity at some point? Although if you don't use the book scanner 40 hours a week each week it might not be a huge concern.

Or is it a situation where if you use four, beyond attaching all those, you're going to generate a lot of heat regardless and it will use a lot of electricity, while not producing much more of an actual result compared to just one floodlight?

bsbob
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Re: Can the lights be too bright?

Post by bsbob » 22 Apr 2014, 19:25

Hm...

Is one 30W or 50W floodlight better than four 10W lights? More, but lower watts vs. less but higher watts.

Or does it not matter? Four would spread out the light source.

ndavidow
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Re: Can the lights be too bright?

Post by ndavidow » 21 Jun 2015, 04:17

Yes it's possible to have too much light, this will overexpose your image (stuff will be washed out and too bright, with low dynamic range). To fix this, reduce the ISO speed (which should also reduce noise). If your ISO is on the lowest setting, you can try stopping the aperture (this normally affects depth of field, but for close range photography the effect should be negligible), or if that's not possible just dim/remove some lights. Read up a little on photography optics.

wmalcolmk
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Re: Can the lights be too bright?

Post by wmalcolmk » 21 Jun 2015, 05:51

How about 63 lights? If you look on the Footsie Bookscanner thread you will see that I am experimenting with LED strip lights, arranged in three lines. It works for me. I will try to do comparisons with GU10 spots, that could be easily fitted to my structure.
Malcolm

wmalcolmk
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Re: Can the lights be too bright?

Post by wmalcolmk » 23 Jun 2015, 11:00

Measuring Platen Lighting

I've started work on improving the lighting in my scanner. First of all I tried to find out from postings on the site, how even it needed to be in practice - no luck. Then I looked to see how people measure how even the lighting is in their scanner build - again I couldn't find anything. If I'm missing a post on this subject, please let me know. In the meantime, I guessed that one of the best places for an even lighting
source is outside, on a cloudy summers day. So I took a white A4 size sheet of paper to the middle of the lawn, and photographed it with one of my Canon Powershot A810 cameras.

The test paper was Jessops ink jet paper A4 matt 120 gsm with a coated surface.
Camera setting were..
White balance = Day light
ISO = 100
Auto focus = on
Metering method = Evaluative

Here is the result, after reduction in file size using the Picasa 3 editor.
Daylight1A.JPG
Daylight1A.JPG (19.5 KiB) Viewed 3291 times
The next operations were carried out at full resolution, using Gimp2 (a free image manipulation program) http://www.gimp.org/downloads/
One of the menu items in this program is Colours/Threshold, which generates a histogram. I assume that this works by looking at the brightness of every pixel in the image, and plotting how many there are at each level. In this case, an image of my paper that was evenly illuminated, would have all the pixels at the same level. This would result in a vertical line somewhere near the middle of the plot. Here is the result for my image.
Daylight1B.JPG
Daylight1B.JPG (34.8 KiB) Viewed 3291 times
When the threshold was set at the peak of the distribution, the following image was produced.
Daylight1C.JPG
Daylight1C.JPG (120.92 KiB) Viewed 3291 times
Any comments?
Is this a suitable method of measuring evenness of lighting?
Is the daylight result a suitable target to aim for?

Malcolm

duerig
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Re: Can the lights be too bright?

Post by duerig » 23 Jun 2015, 11:43

I really like the idea of trying to quantify how even the lighting is. Opening up an image and eyeballing it only gets you so far. Because of some previous tests, I happened to have a pair of images taken with an Archivist using two different kinds of bulbs. So I did a quick threshold following your instructions and took screenshots of the results.
soraa.png
SORAA 00919 bulbs in Archivist
green-creative.png
Green Creative 95350 bulbs in Archivist
So a few differences pop out. First, the shape of the threshold picture was unexpected to me. There are two bulbs above the platen, one on the left and one on the right. So it seems that the overlap between them in the middle is brighter. And this is especially so near the top (closer to the bulbs) and the bottom (maybe more reflected light?). Your test had a single circle in the middle which I presume was the sun as a single source of light.

The threshold on these is much whiter than yours, but I think that is probably because I just used random printed paper rather than the callibrated grey card you used.

Both of these seem to have a tighter distribution than the sun. But the Green Creative seems to have slightly less variance than the SORAA bulb. I think that this is probably down to the difference in projection angle between the two bulbs. The SORAA is a spotlight before it hits the lenses with a narrow beam. The Green Creative bulb has a wider beam.

But we may not be comparing apples to apples here anyhow. I took these pictures with a different camera using different settings at a different angle than yours. When I get time, I would like to do some more systematic tests using the same camera to get photos in the sun and using different lights. This technique of evaluating light evenness looks very promising.

-D

cday
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Re: Can the lights be too bright?

Post by cday » 23 Jun 2015, 12:40

duerig wrote:I really like the idea of trying to quantify how even the lighting is.
Thresholding at the peak intensity in the histogram produces a dramatic plot, but wouldn't the evenness of the overall illumination be better represented by plots at different intensity values? Ideally these might be superimposed to show intensity with respect to position on the reference sheet, although that would require converting each plot to an outline in some way...

Another thought: Given that sunlight is parallel light, wouldn't one expect or at least hope for a very even light distribution when photographing a reference sheet in good sunlight or well diffused light on a bright but overcast day? If that result isn't obtained, doesn't it suggest that some other factor or factors are in play, possibly related to the characteristics of the camera sensor or the lens??

wmalcolmk
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Re: Can the lights be too bright?

Post by wmalcolmk » 23 Jun 2015, 13:30

Questions/comments from duerig and cday

"...single circle in the middle which I presume was the sun as a single source of light..."
I took the photo with 100 percent cloud, so I think the illumination was effectively from a translucent layer with the sun behind it.

"...threshold on these is much whiter..."
I didn't use a grey card, just good quality white paper. The threshold is just dependent on the camera exposure. Mine tries to make the scene grey.

"...wouldn't the evenness of the overall illumination be better represented by plots at different intensity values?..."
I think the width of the histogram is the best measure of evenness of illumination, since perfect illumination would result in every pixel having the same brightness - giving a single vertical line on the histogram.

My initial conclusion is that the eye would judge that cloudy daylight gives even enough illumination, so we should be looking to improve some other aspect of the scanner if results fall short - as cday said.

Malcolm

qv_
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Re: Can the lights be too bright?

Post by qv_ » 23 Jun 2015, 13:41

duerig wrote:I Your test had a single circle in the middle which I presume was the sun as a single source of light
The circle is made by the lens. The piqture is darker on the edge on almost every lens.
You can get good results if you use a Full Frame lens on a APS camera. (a prime like Canon EF50 f1,4 on a 550D) Then you just use the midle part of the lens and therefore get more even light in the corner.

/Jan

qv_
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Re: Can the lights be too bright?

Post by qv_ » 23 Jun 2015, 13:49


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