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

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by mhr
16 Aug 2013, 09:05
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

Obviously these examples suffer from bad influence of the page holders at the corners, which were used to rapidly get some example pictures and the pictures have been truncated by the calibration grid as well. In addition the large keystoning takes parts of the pictures out of focus. By careful desi...
by mhr
16 Aug 2013, 08:59
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

As a last example the picture of a flyer
page3a.jpg
Original picture of flyer page3a.ppm
and the corrected version
page3b.jpg
Corrected flyer page3b.ppm
by mhr
16 Aug 2013, 08:56
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

And here is a picture of another laser printout
page2a.jpg
Original picture of the GNU License page2a.ppm
and the corrected version
page2b.jpg
Corrected picture page2b.ppm
by mhr
16 Aug 2013, 08:52
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

Now the command ppmunwarp -d deform.bin page_orig.ppm | ppmwhitebalancing -d color2.bin > page_corrected.ppm can be used to dewarp and color correct the pictures of interest. My first example page is a picture full of numbers, which I use to get the autofocus of my camera right: page1a.jpg After cor...
by mhr
16 Aug 2013, 08:46
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

The picture of my simple gray card gray.jpg in combination with the calibration grid gridcorr_a.jpg can be used to obtain color correction information and unwarping information with the following commands: ppmunwarp -gm 0 -m check.ppm grid.ppm > deform.bin ppmwhitebalance -nx 40 gray.ppm > color1.bi...
by mhr
16 Aug 2013, 08:24
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

In the following I want to concretize the steps I have in mind to color correct and unwarp pictures with the two utilities ppmwhitebalancing and ppmunwarp . This example is just rapid prototyping, the pictures are not totally in focus, the keystoning is quite large and the lighting conditions are fa...
by mhr
16 Aug 2013, 08:19
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Re: Grid based white balancing of images

The program has several options to control its behaviour. The main goal is to color correct pictures by shooting an additional picture of a homogeneous gray card as color calibration information. The program places a control point grid upon the calibration picture of nx x ny points (see options -nx ...
by mhr
16 Aug 2013, 07:50
Forum: Tutorials/How-To's
Topic: Grid based white balancing of images
Replies: 9
Views: 6760

Grid based white balancing of images

After the discussion in the thread http://www.diybookscanner.org/forum/viewtopic.php?f=19&t=2795 , I decided to write a small command line tool for grid based white balancing of images with a calibrationg gray card. The source code ppmwhitebalance.cc.txt is written in the same spirit as the unwarp u...
by mhr
16 Aug 2013, 07:40
Forum: Tutorials/How-To's
Topic: Dewarping with a regular calibration point grid
Replies: 18
Views: 20416

Re: Dewarping with a regular calibration point grid

Just another update with a minor bugfix.
I noted that the option '-gm' doesn't accept a zero value, which is useful to avoid boundaries
around detected grid points.
ppmunwarp.cc.txt
Version 1.2 of ppmunwarp
(63.18 KiB) Downloaded 299 times
by mhr
14 Aug 2013, 03:05
Forum: Programs, Software releases, and more.
Topic: Scantailor preprocess script
Replies: 30
Views: 18490

Re: Scantailor preprocess script

I updated my program ppmunwarp to version 1.1 with calculation of the correct PPI information for the unwarped pages.
You can find the program at http://www.diybookscanner.org/forum/vie ... 464#p16464.

Have fun!