hugin-devs team mailing list archive

[Bruno Postle <696668@xxxxxxxxxxxxxxxxxx>]

Regarding optimisation of FoV, the problem with 'v' reducing to zero
only happens with very narrow panoramas .

Think about the panorama as segment of the 'sphere'. With a narrow field
of view this segment is very similar to a flat surface, and the photos
will fit whatever 'v' you give them.

With a scene with a large field of view (>90) the segment is
significantly curved and it isn't possible to get a 'better' fit by
simply reducing 'v' for the photos.

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https://bugs.launchpad.net/bugs/696668

Title:
  smart optimisation in the assistant is non-optimal

Status in Hugin - Panorama Tools GUI:
  Triaged

Bug description:
  The stages of the existing smart optimisation that happen when you use
  Align... in the Assistant tab are:

  First it optimises just positions, if the final panorama is 360° then
  it will optimise field of view of the photos in the next step.

  It looks at the spread of control points and either optimises just 'b'
  or 'a,b,c' lens parameters depending on this spread.

  If the photos are wider than 60° then d,e will be optimised too.

  It does some checks with the result of this second step, if the
  v,a,b,c,d,e parameters are not credible then it backs out and
  optimises the project again but with less parameters.

  (from SmartOptimise::smartOptimize in
  src/hugin_base/algorithms/optimizer/PTOptimizer.cpp)

  Looking at this code, some of the default thresholds and heuristics
  could be better:

  I think it is safe to optimise field of view if the panorama is
  greater than about 150° (and if the panorama is not a single stack).

  The a,b,c thresholds are much too high.

  High a,b,c values can be an indication that the lens type is
  incorrect, perhaps at this point it would be useful to run another
  optimisation with fisheye/rectilinear and see which gives the best
  results.

  The straighten function is run but this doesn't work unless there is
  some horizontal spread of photos (i.e. a vertical panorama fails) see
  Bug #679282 (sf-2851956)

  a,b,c,d,e should never be optimised when the initial alignment
  indicates that we have a single stack (i.e. the assistant is currently
  broken with all single stack projects).

  The d,e threshold should be a proportion of the photo width rather
  than a pixel value.

  Photometric optimisation is always performed, but this is almost
  always a mess unless there is a good geometrical alignment. So if the
  alignment is bad, then photometric optimisation should be skipped.

  Photometric alignment needs significant vignetting and/or bracketed
  exposures to be able to calculate the camera response curve, 'bad'
  response curves result in 'banding' or 'posterisation' artefacts. The
  Assistant tab could be refined to back-out of photometric alignment if
  the vignetting turns out to be low or there is no EV variation.

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