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

Flat fields to correct for uneven illumination -- has anyone tried this?

All about lighting. LED, CFL, Halogen, Other? Questions and info about lighting go here.
Post Reply
User avatar
Mohib
Posts: 87
Joined: 05 Apr 2014, 21:15
Number of books owned: 0
Country: Canada

Flat fields to correct for uneven illumination -- has anyone tried this?

Post by Mohib » 16 Apr 2017, 22:45

There is a well known process -- flat fielding -- that is used to correct for uneven illumination in images in scientific and astronomical images. See here:

http://imagej.net/Image_Intensity_Proce ... correction

I'm wondering if anyone has tried this method to eliminate or reduce illumination gradients that many lighting configurations? I'm sure it is a very compute intensive process but is something that could be useful when it's important to get evenly lit images and lighting is not optimal.

mera461
Posts: 7
Joined: 27 Dec 2013, 07:08
Number of books owned: 0
Country: Denmark

Re: Flat fields to correct for uneven illumination -- has anyone tried this?

Post by mera461 » 18 Apr 2017, 16:15

You could try CLAHE (Contrast Limited Adaptive Histogram Equalization). With OpenCV it is 6 lines of python: https://opencv-python-tutroals.readthed ... ation.html

User avatar
daniel_reetz
Posts: 2770
Joined: 03 Jun 2009, 13:56
E-book readers owned: Used to have a PRS-500
Number of books owned: 600
Country: United States
Contact:

Re: Flat fields to correct for uneven illumination -- has anyone tried this?

Post by daniel_reetz » 11 Nov 2017, 20:00

Yeah, in the very first scanner, Aaron Clarke and I would take a picture of a blank piece of paper, and then subtract the inverse of that from the page image. It works, as long as your cameras have fixed settings and the camera-platen relationship doesn't change. If it changes at all, you need a new reference image. If you want to try this, it's easy to do in Photoshop with just two layers.

If you're only interested in correcting for vignetting or low-frequency falloff, you can also blur an image of a blank piece of paper and subtract that.

Here are some other weird ideas around lighting: http://www.danreetz.com/blog/2011/01/05 ... -scanning/

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest