Hi, > > [...] Unfortunately the corrections that are computed by lensfun > > contain "fuzziness" (they are kind of non-continuous due to big > > rounding errors), [...] > > Could you elaborate on that? What is the source of those rounding > errors? >
Here is an example of the distorsion values that are returned from lensfun (without TCA) for contiguous pixels: x,y=0,3271 pr=78.314850,3219.129150 pg=78.314850,3219.085693 x,y=0,3272 pr=78.114517,3220.230225 pg=78.114517,3220.135010 x,y=0,3273 pr=77.991783,3221.279785 pg=77.991783,3221.235840 x,y=0,3274 pr=78.102600,3222.174561 pg=78.102600,3222.130615 x,y=0,3275 pr=78.213219,3223.069336 pg=78.213219,3223.180176 x,y=0,3276 pr=78.324234,3223.963867 pg=78.324234,3224.074707 x,y=0,3277 pr=78.201881,3225.013672 pg=78.201881,3224.969482 x,y=0,3278 pr=78.079147,3226.063477 pg=78.079147,3226.019043 x,y=0,3279 pr=78.189957,3226.958008 pg=78.189957,3226.913574 They indicate where to pick up red and green values in the input for an output pixel (x,y). The x component should be almost-constant or at least monotone so the rounding error is about 0.3. Dunno where it comes from yet. They use Newton's method but I already tried to increase the iteration count. > > [...] > > > > The general idea for the fitting hasn't changed, but you should > > notice improvements because the method for the evaluation of color > > shifts has changed. The fitting is now computed based on better > > estimations, with proper weighting. For example, a large > > pseudo-uniform blue sky does not have a bad influence on shift > > estimations. > > Does this mean you could use your method to create an improved > stand-alone tca_correct? I'm working on that now. Assuming the shifts are radial is a probably a reasonable assumption in many cases. > > About the fitting itself, the applied red and blue color shift are > > resolved as 2-dimensional polynomials of degree 4 (hard-coded but > > can be modified in the source). That is, a sum of x^n*y^m > > components with n + m <= 4. > > Is it really necessary to take non-radial components into account? > >From my experience with distortion, I can hardly imagine this. I think correcting small motion trails (including camera's shaking) or variations in scene's depth may require non-radial components. Some pictures taken with perfectly standard lenses seem to need it. > Me too. I hope that I convince the devs some day to reduce the two > TCA sliders to one. How would you determine the ratio between the two then, if you don't rely on automatic methods? Profile based? Stéphane ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/NeoTech _______________________________________________ darktable-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/darktable-devel
