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, 4 insertions, 0 deletions

diff --git a/configure b/configure
index b1a4dcfc42..5783407bdc 100755
--- a/configure
+++ b/configure
@@ -239,6 +239,7 @@ External library support:
   --enable-libilbc         enable iLBC de/encoding via libilbc [no]
   --enable-libjack         enable JACK audio sound server [no]
   --enable-libkvazaar      enable HEVC encoding via libkvazaar [no]
+  --enable-liblensfun      enable lensfun lens correction [no]
   --enable-libmodplug      enable ModPlug via libmodplug [no]
   --enable-libmp3lame      enable MP3 encoding via libmp3lame [no]
   --enable-libopencore-amrnb enable AMR-NB de/encoding via libopencore-amrnb [no]
@@ -1656,6 +1657,7 @@ EXTERNAL_LIBRARY_NONFREE_LIST="
 
 EXTERNAL_LIBRARY_VERSION3_LIST="
     gmp
+    liblensfun
     libopencore_amrnb
     libopencore_amrwb
     libvmaf
@@ -3353,6 +3355,7 @@ hqdn3d_filter_deps="gpl"
 interlace_filter_deps="gpl"
 kerndeint_filter_deps="gpl"
 ladspa_filter_deps="ladspa libdl"
+lensfun_filter_deps="liblensfun version3"
 lv2_filter_deps="lv2"
 mcdeint_filter_deps="avcodec gpl"
 movie_filter_deps="avcodec avformat"
@@ -6023,6 +6026,7 @@ enabled libgsm            && { for gsm_hdr in "gsm.h" "gsm/gsm.h"; do
                                done || die "ERROR: libgsm not found"; }
 enabled libilbc           && require libilbc ilbc.h WebRtcIlbcfix_InitDecode -lilbc $pthreads_extralibs
 enabled libkvazaar        && require_pkg_config libkvazaar "kvazaar >= 0.8.1" kvazaar.h kvz_api_get
+enabled liblensfun        && require_pkg_config liblensfun lensfun lensfun.h lf_db_new
 # While it may appear that require is being used as a pkg-config
 # fallback for libmfx, it is actually being used to detect a different
 # installation route altogether.  If libmfx is installed via the Intel