Add lensfun filter

Lensfun is a library that applies lens correction to an image using a
database of cameras/lenses (you provide the camera and lens models, and
it uses the corresponding database entry's parameters to apply lens
correction). It is licensed under LGPL3.

The lensfun filter utilizes the lensfun library to apply lens
correction to videos as well as images.

This filter was created out of necessity since I wanted to apply lens
correction to a video and the lenscorrection filter did not work for me.

While this filter requires little info from the user to apply lens
correction, the flaw is that lensfun is intended to be used on indvidual
images. When used on a video, the parameters such as focal length is
constant, so lens correction may fail on videos where the camera's focal
length changes (zooming in or out via zoom lens). To use this filter
correctly on videos where such parameters change, timeline editing may
be used since this filter supports it.

Note that valgrind shows a small memory leak which is not from this
filter but from the lensfun library (memory is allocated when loading
the lensfun database but it somehow isn't deallocated even during
cleanup; it is briefly created in the init function of the filter, and
destroyed before the init function returns). This may have been fixed by
the latest commit in the lensfun repository; the current latest release
of lensfun is almost 3 years ago.

Bi-Linear interpolation is used by default as lanczos interpolation
shows more artifacts in the corrected image in my tests.

The lanczos interpolation is derived from lenstool's implementation of
lanczos interpolation. Lenstool is an app within the lensfun repository
which is licensed under GPL3.

v2 of this patch fixes license notice in libavfilter/vf_lensfun.c

v3 of this patch fixes code style and dependency to gplv3 (thanks to
Paul B Mahol for pointing out the mentioned issues).

v4 of this patch fixes more code style issues that were missed in
v3.

v5 of this patch adds line breaks to some of the documentation in
doc/filters.texi (thanks to Gyan Doshi for pointing out the issue).

v6 of this patch fixes more problems (thanks to Moritz Barsnick for
pointing them out).

v7 of this patch fixes use of sqrt() (changed to sqrtf(); thanks to
Moritz Barsnick for pointing this out). Also should be rebased off of
latest master branch commits at this point.

Signed-off-by: Stephen Seo <seo.disparate@gmail.com>

1 files changed, 118 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 49895ff947..9d8f88ddcf 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -10700,6 +10700,124 @@ The formula that generates the correction is:
 where @var{r_0} is halve of the image diagonal and @var{r_src} and @var{r_tgt} are the
 distances from the focal point in the source and target images, respectively.
 
+@section lensfun
+
+Apply lens correction via the lensfun library (@url{http://lensfun.sourceforge.net/}).
+
+The @code{lensfun} filter requires the camera make, camera model, and lens model
+to apply the lens correction. The filter will load the lensfun database and
+query it to find the corresponding camera and lens entries in the database. As
+long as these entries can be found with the given options, the filter can
+perform corrections on frames. Note that incomplete strings will result in the
+filter choosing the best match with the given options, and the filter will
+output the chosen camera and lens models (logged with level "info"). You must
+provide the make, camera model, and lens model as they are required.
+
+The filter accepts the following options:
+
+@table @option
+@item make
+The make of the camera (for example, "Canon"). This option is required.
+
+@item model
+The model of the camera (for example, "Canon EOS 100D"). This option is
+required.
+
+@item lens_model
+The model of the lens (for example, "Canon EF-S 18-55mm f/3.5-5.6 IS STM"). This
+option is required.
+
+@item mode
+The type of correction to apply. The following values are valid options:
+
+@table @samp
+@item vignetting
+Enables fixing lens vignetting.
+
+@item geometry
+Enables fixing lens geometry. This is the default.
+
+@item subpixel
+Enables fixing chromatic aberrations.
+
+@item vig_geo
+Enables fixing lens vignetting and lens geometry.
+
+@item vig_subpixel
+Enables fixing lens vignetting and chromatic aberrations.
+
+@item distortion
+Enables fixing both lens geometry and chromatic aberrations.
+
+@item all
+Enables all possible corrections.
+
+@end table
+@item focal_length
+The focal length of the image/video (zoom; expected constant for video). For
+example, a 18--55mm lens has focal length range of [18--55], so a value in that
+range should be chosen when using that lens. Default 18.
+
+@item aperture
+The aperture of the image/video (expected constant for video). Note that
+aperture is only used for vignetting correction. Default 3.5.
+
+@item focus_distance
+The focus distance of the image/video (expected constant for video). Note that
+focus distance is only used for vignetting and only slightly affects the
+vignetting correction process. If unknown, leave it at the default value (which
+is 1000).
+
+@item target_geometry
+The target geometry of the output image/video. The following values are valid
+options:
+
+@table @samp
+@item rectilinear (default)
+@item fisheye
+@item panoramic
+@item equirectangular
+@item fisheye_orthographic
+@item fisheye_stereographic
+@item fisheye_equisolid
+@item fisheye_thoby
+@end table
+@item reverse
+Apply the reverse of image correction (instead of correcting distortion, apply
+it).
+
+@item interpolation
+The type of interpolation used when correcting distortion. The following values
+are valid options:
+
+@table @samp
+@item nearest
+@item linear (default)
+@item lanczos
+@end table
+@end table
+
+@subsection Examples
+
+@itemize
+@item
+Apply lens correction with make "Canon", camera model "Canon EOS 100D", and lens
+model "Canon EF-S 18-55mm f/3.5-5.6 IS STM" with focal length of "18" and
+aperture of "8.0".
+
+@example
+ffmpeg -i input.mov -vf lensfun=make=Canon:model="Canon EOS 100D":lens_model="Canon EF-S 18-55mm f/3.5-5.6 IS STM":focal_length=18:aperture=8 -c:v h264 -b:v 8000k output.mov
+@end example
+
+@item
+Apply the same as before, but only for the first 5 seconds of video.
+
+@example
+ffmpeg -i input.mov -vf lensfun=make=Canon:model="Canon EOS 100D":lens_model="Canon EF-S 18-55mm f/3.5-5.6 IS STM":focal_length=18:aperture=8:enable='lte(t\,5)' -c:v h264 -b:v 8000k output.mov
+@end example
+
+@end itemize
+
 @section libvmaf
 
 Obtain the VMAF (Video Multi-Method Assessment Fusion)