Public Lab Research note


A Method for distorting Mobius Action Cam imagery in GIMP (FOSS)

by eustatic | November 11, 2014 21:31 | 157 views | 4 comments | #11336 | 157 views | 4 comments | #11336 11 Nov 21:31

What I want to do

Make Mapknitter maps with infragram and another mobius (so light!)

So Mat suggested a method of distorting graph paper until it looked right.

Chris Fastie has laid out the limitations of infragram maps --the edges need to be cropped

I think GIMP crops edges.

I want to use this because I'm too poor for photoshop, and freedom rules.

My attempt and results

There are two "Lens Distortion" filters in GIMP

Filters -> Distort -> Lens Distortion

"Main" and "Edge"

Here is the original image

IMAG0021_test_grid_farther_away.JPG

Main -40

IMAG0021_test_grid_farther_away_40.JPG

Main -41 edges +5

IMAG0021_test_grid_farther_away_41_5.JPG

Main -42 edges 0

IMAG0021_test_grid_farther_away_42.JPG

Main -50 edges 0

IMAG0021_test_grid_farther_away_50.JPG

Questions and next steps

What do people think?

Here's a shoreline map with no distortion, -34, and -41 5.

BSJ_shore_norm.JPG

BSJ_shore_norm_34.JPG

BSJ_shore__41_5.JPG


4 Comments

I was wondering if we could add this as a feature to http://Infragram.org (and potentially MapKnitter in the future!) by writing a JavaScript Canvas module that removes lens distortion from an image.

I might've thought to do it in the same way we use Canvas to distort (https://github.com/publiclab/mapknitter/blob/master/public/cartagen/src/warper/image.js#L344)

but these days, we might be able to write a WebGL module to do it even faster.

This person has ported a lens distortion shader (http://devlog-martinsh.blogspot.ca/2011/10/glsl-cubic-lens-distortion.html) to WebGL:

https://medium.com/@mattdesl/filmic-effects-for-webgl-9dab4bc899dc

The shaders are here: https://github.com/mattdesl/filmic-gl/tree/master/demos/shaders

hmmm! I don't know webgl well, but it seems promising?

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https://mapknitter.org/maps/bayou-st-john-shoreline-nov-2014

I also do not know webgl, but

this would be an excellent option to those softwares.

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I've been using the Mobius Cam with both standard and Wide Angled Lens for KAP and soon UAV. I solved the lens distortion issue thanks to a workflow suggested to me in the comment section of my KAP research note- (see bottom 3 comments in the thread) http://publiclab.org/notes/code4maine/06-25-2014/kap-test-for-invasives-monitoring-project Basically, there is a Plugin called "BIMP" that allows you to do batch processing in GIMP. You do need to set the distortion values manually however, by taking a screenshot and copying the values into the plugin dialog. There are other FOSS programs for batch processing like DIGIKAM and HUGIN Panorama editor that I havent tried yet. However, considering the popularity of GIMP, it may be worth designing our own plugin with Mapknitter (and/or Infragram) support as more and more people use the Mobius Cam.

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just getting back into this again. ajawitz, thanks for your BIMP recommendation.

i think i was going to figure out how to batch process

channel switching R-B, red boost to 130, then contrast boost

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