I mean http://en.wikipedia.org/wiki/Derivative
You don't plot x(r) but x'(r). This way, the colour blue means "barrel" and red means "pincushion" (or the other way round). Look at the section "How to read a distortion graph" on <http://toothwalker.org/optics/distortion.html>. And look at the formulae at <http://lensfun.berlios.de/manual/group__Lens.html#gaa505e04666a189274ba66316697e308e>. Speaking in terms of these formulae, you plot |r_d - r_u|. This is the left-hand plot on the first link. But more interesting in my opinion is (r_d - r_u) / r_u, and this differentiated with respect to r_u. In practice, you can realise that by getting the model and its parameters out of Lensfun (instead of using applyGeometryDistortion()), and implement the derivatives of the formulae yourself. For example for the PTLens model, you get f(r) = 3*a*r**2 + 2*b*r + c. ------------------------------------------------------------------------------ Put Bad Developers to Shame Dominate Development with Jenkins Continuous Integration Continuously Automate Build, Test & Deployment Start a new project now. Try Jenkins in the cloud. http://p.sf.net/sfu/13600_Cloudbees _______________________________________________ Lensfun-users mailing list Lensfun-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lensfun-users
