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[tmodes <2000019@xxxxxxxxxxxxxxxxxx>]

** Changed in: hugin
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/2000019

Title:
  Take into account digital zoom ratio EXIF tag in the computation of
  the HFOV

Status in Hugin:
  Fix Released

Bug description:
  The horizontal field of view (HFOV) property of a picture is critical
  to allow proper stitching. Inadequate values forbid automatic
  detection of control points, which is a central piece (and major added
  value) in Hugin's, and hence breaks the automated stitching workflow.
  Thankfully, Hugin automatically computes the HFOV value for pictures
  with valid EXIF data. Again, this is a great benefit which avoids
  manual computation for each lense and lengthy entry of manual data.

  In traditional cameras, the HFOV is mainly a function of the lense's
  focal length: adjusting the zoom between two shots with the same
  camera results in different focal lengths for each shot. This
  information is correctly read and interpreted into distinct HFOV by
  Hugin. In contrast, modern digital cameras, such as samsung cell
  phones to cite just one widely-spread example, typically feature fixed
  lenses with a unique focal length. Yet, it is still possible to take
  shots with different zoom factors (or, say, to be given pictures to
  stitch that were taken with such a device and with different zoom
  factors...). In this case, the focal length information is identical
  for all shots and the zoom information is encoded in a distinct EXIF
  tag, called the 'Digital Zoom Ratio'. Currently, it seems that Hugin
  doesn't take advantage of this tag, hence wrongly assuming that all
  pictures taken with the same 'digital camera' have an identical HFOV.
  This causes Hugin to be unable to stitch the pictures, because it
  typically fails to find control points.

  This might be relatively straightforward to fix given that:
    - The digital zoom ratio affects the HFOV in a simple manner, so it should be possible to compute the HFOV by taking into account both the lense's focal length and the digital zoom ratio (when available)
    - Hugin seems to rely on Exiv2 to acquire EXIF data from files, which supports the 'Digital Zoom Ratio' tag, so it should be possible to access this tag with the existing infrastructure. I checked that the command `exiv2 -pt image.jpg` on my images return the tag `Exif.Photo.DigitalZoomRatio` with the correct value. The same values are also read by Exiftool (checked with command `exiftool image.jpg`).

  I'm using Hugin 2021.0.0.52df0f76c700 (built with Exiv2 0.27.5) on
  Ubuntu 22.04.1. The version of Exiv2 that I used in the command line
  is also 0.27.5.

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