Straight

Pierre Drap

About this app

Straight tells the story of radial lens distortion and of the theorem that
undoes it exactly, published in Sensors in 2016.

Four short chapters, to be handled more than read.

1. Seeing the curvature. Take the place of the glass: one slider bends a
composition of straight lines, barrel one way, pincushion the other, and
straightening it again shows the mirror polynomial that did the work.

2. Measuring the curvature. Stretch Brown's plumb lines and calibrate a
lens by eye, then let least squares do the same thing and compare. The eye
gets there in a handful of seconds; the machine wins at the fourth decimal.

3. The exact mirror. Watch the inverse series collapse, or diverge. Its
coefficients hide the Fuss-Catalan numbers, the ones that count ternary
trees, and the chapter says why.

4. The bridge and the tool. Convert between Metashape, OpenCV, millimetres
and pixels, and read the nine mirror coefficients with the residual that
certifies them. The tool and its Python module are gifts: the module is
printed in full, with no dependency, and it self-tests on the paper's
reference data.

Four languages, no account, no advertising, no data collection, and no
network permission at all: it works in airplane mode, and you can check
that yourself.

Based on P. Drap and J. Lefevre, "An Exact Formula for Calculating Inverse
Radial Lens Distortions", Sensors 2016, 16(6), 807,
doi 10.3390/s16060807. Epigraph quoted from F. Devernay and O. Faugeras,
2001.

IMAGE4D, image4d.fr

What’s new

First release.