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

Recommendation regarding brightness

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shijualex
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Recommendation regarding brightness

Post by shijualex » 04 Feb 2021, 14:24

Hello All

I have a question regarding the amount of light (or brightness) that we need to keep while capturing the photos (using digital camera).

As you all know by adjusting the shutter speed/ISO/Aperture we can control the brightness of a photo. But, is there is any recommended values for the brightness for digital archiving? While handling documents from different decades I am finding it difficult to judge and decide on a standard value for brightness. Requesting suggestions from experience.

dpc
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Location: Issaquah, WA

Re: Recommendation regarding brightness

Post by dpc » 05 Feb 2021, 13:59

Probably not that critical if you're going to scanning black text on a white page and then post-processing with something like ScanTailor that binarizes the output. If you're looking for something more accurate than that you could always use an 18% gray card to set things up.

I remember reading through threads years ago from a user named "Misty" that discussed a lot about color correction and proper lighting in these forums (I believe she was scanning comic books, or some such). You may want to search for those posts and see if that provides any insight for the sort of materials that you plan to scan.

The majority of my lighting issues when photographing books with colored photographs have been trying to compensate for uneven lighting across the page, rather than the overall level of brightness.

shijualex
Posts: 9
Joined: 17 May 2013, 09:50
Number of books owned: 3000
Country: India
Location: Bangalore, India
Contact:

Re: Recommendation regarding brightness

Post by shijualex » 05 Feb 2021, 23:41

Thank you. The documents I handle include color images also.

I will try the color card option you suggested. Also let me search the forum once more to locate the posts by "Misty". Thanks once again.

jaffamuffin
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Re: Recommendation regarding brightness

Post by jaffamuffin » 09 Feb 2021, 11:08

get a colour card like xrite colour checker and set your exposure and colour balance so the greytones are neutral (i.e. R,G,B all the same value) and set the first grey square to be 200,200,200 etc. See here https://xritephoto.com/ph_product_overv ... ortID=5159 You may need to do this post process depending how much control your camera has.

jaffamuffin
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Re: Recommendation regarding brightness

Post by jaffamuffin » 09 Feb 2021, 11:14

dpc wrote:
05 Feb 2021, 13:59

The majority of my lighting issues when photographing books with colored photographs have been trying to compensate for uneven lighting across the page, rather than the overall level of brightness.
you can compensate to some extent this problem by photographing a flat white sheet and then subtracting this from subsequent images captured which will 'cancel out' any uneven brightness fluctuations. Look up flat fielding https://en.wikipedia.org/wiki/Flat-field_correction

dpc
Posts: 343
Joined: 01 Apr 2011, 18:05
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Location: Issaquah, WA

Re: Recommendation regarding brightness

Post by dpc » 09 Feb 2021, 12:32

jaffamuffin wrote:
09 Feb 2021, 11:14
you can compensate to some extent this problem by photographing a flat white sheet..
Yep. That's the technique I use to mitigate that problem. The first photo taken by each camera are of blank reference pages. The post-processing software that I developed does this correction automatically in the background as new images are acquired from the scanner. This technique requires that the light and camera position/direction remain constant relative to the platen throughout the scan, which is usually the case with most scanner designs.

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