Add auto-alignment for HDR bracket merging

.ci/Brewfile

@@ -48,6 +48,7 @@ brew 'lua@5.4', link: true, overwrite: true
 brew 'libomp', link: true
 brew 'ninja'
 brew 'onnxruntime'
+brew 'opencv'
 brew 'openexr'
 brew 'openjpeg'
 brew 'osm-gps-map'

.ci/Dockerfile

@@ -89,6 +89,11 @@ RUN rm -rf /var/lib/apt/lists/* && apt-get update && \
     liblua5.2-dev \
     liblua5.3-dev \
     libomp-$LLVM_VER-dev \
+    libopencv-calib3d-dev \
+    libopencv-core-dev \
+    libopencv-features2d-dev \
+    libopencv-flann-dev \
+    libopencv-imgproc-dev \
     libopenexr-dev \
     libopenjp2-7-dev \
     libosmgpsmap-1.0-dev \

.github/workflows/ci.yml

@@ -143,6 +143,11 @@ jobs:
             liblensfun-dev \
             liblua5.4-dev \
             libonnxruntime-dev \
+            libopencv-calib3d-dev \
+            libopencv-core-dev \
+            libopencv-features2d-dev \
+            libopencv-flann-dev \
+            libopencv-imgproc-dev \
             libopenexr-dev \
             libopenjp2-7-dev \
             libosmgpsmap-1.0-dev \
@@ -269,6 +274,7 @@ jobs:
             libxml2:p
             lua54:p
             omp:p
+            opencv:p
             openexr:p
             openjpeg2:p
             osm-gps-map:p

.github/workflows/nightly.yml

@@ -72,6 +72,11 @@ jobs:
             liblensfun-bin \
             liblensfun-data-v1 \
             liblensfun1 \
+            libopencv-calib3d-dev \
+            libopencv-core-dev \
+            libopencv-features2d-dev \
+            libopencv-flann-dev \
+            libopencv-imgproc-dev \
             libosmgpsmap-1.0-dev \
             libpango1.0-dev \
             libpng-dev \
@@ -258,6 +263,7 @@ jobs:
             libxml2:p
             lua54:p
             omp:p
+            opencv:p
             openexr:p
             openjpeg2:p
             osm-gps-map:p

DefineOptions.cmake

@@ -35,6 +35,7 @@ option(BUILD_NOISE_TOOLS "Build tools for generating noise profiles" OFF)
 option(BUILD_CURVE_TOOLS "Build tools for generating base and tone curves" OFF)
 option(USE_GMIC "Use G'MIC image processing framework." ON)
 option(USE_ICU "Use ICU - International Components for Unicode." ON)
+option(USE_OPENCV "Use OpenCV for HDR exposure-bracket auto-alignment." ON)
 option(FORCE_COLORED_OUTPUT "Always produce ANSI-colored output (GNU/Clang only)." OFF)
 option(USE_SDL2 "Enable SDL2 support" ON)
 

README.md

@@ -260,6 +260,7 @@ Optional dependencies (minimum version):
 * libheif 1.13.0 *(for HEIF import & export; also for AVIF import if no libavif)*
 * libjxl 0.7.0 *(for JPEG XL import & export)*
 * WebP 0.3.0 *(for WebP import & export)*
+* OpenCV 4 — only the core, imgproc, features2d, flann and calib3d modules *(for HDR exposure-bracket auto-alignment)*
 
 Optional dependencies (no version requirement):
 * colord, Xatom *(for fetching the system display color profile)*

build.sh

@@ -35,7 +35,7 @@ CMAKE_OPTIONS_FROM_CMDLINE=""
 
 PRINT_HELP=0
 
-FEATURES="AI CAMERA COLORD GMIC GRAPHICSMAGICK IMAGEMAGICK JXL KWALLET LIBSECRET LUA MAC_INTEGRATION MAP OPENCL OPENEXR OPENMP UNITY WEBP"
+FEATURES="AI CAMERA COLORD GMIC GRAPHICSMAGICK IMAGEMAGICK JXL KWALLET LIBSECRET LUA MAC_INTEGRATION MAP OPENCL OPENCV OPENEXR OPENMP UNITY WEBP"
 
 # prepare a lowercase version with a space before and after
 # it's very important for parse_feature, has no impact in for loop expansions

data/darktableconfig.xml.in

@@ -14,6 +14,7 @@
   </dttab>
   <dttab name="processing" title="processing">
     <section name="general" title="image processing"/>
+    <section name="hdr_alignment" title="HDR alignment"/>
     <section name="cpugpu" title="CPU / memory"/>
     <section name="opencl" title="OpenCL GPU acceleration"/>
     <section name="platform" title="OpenCL drivers"/>
@@ -384,6 +385,55 @@
     <shortdescription>do not set the 'uncategorized' entry for tags</shortdescription>
     <longdescription>do not set the 'uncategorized' entry for tags which do not have children</longdescription>
   </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_auto_align</name>
+    <type>bool</type>
+    <default>true</default>
+    <shortdescription>auto-align frames when merging HDR brackets</shortdescription>
+    <longdescription>register and warp exposure brackets onto a reference frame before merging, removing ghosting caused by a shaky tripod or handheld shots.\nonly effective when darktable is built with OpenCV.</longdescription>
+  </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_auto_reference</name>
+    <type>bool</type>
+    <default>false</default>
+    <shortdescription>pick the HDR alignment reference automatically</shortdescription>
+    <longdescription>before merging, examine every bracket and align to the one richest in detail instead of the first frame.\nimproves alignment when the first exposure is a poor template, at the cost of one extra decode pass over the frames.\nrequires auto-align and an OpenCV build.</longdescription>
+  </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_proxy_scale</name>
+    <type min="0.25" max="1.0">float</type>
+    <default>0.625</default>
+    <shortdescription>alignment detail (proxy scale)</shortdescription>
+    <longdescription>fraction of the full sensor resolution at which feature detection and alignment are computed.\nhigher values find more, more distinctive features (better on repetitive or low-contrast scenes) but cost roughly (scale / 0.5)^2 more time and memory.\n0.5 restores the legacy speed; 0.625 matches the reference prototype.</longdescription>
+  </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_feature_gamma</name>
+    <type min="1.0" max="6.0">float</type>
+    <default>2.2</default>
+    <shortdescription>shadow lift for feature detection (gamma)</shortdescription>
+    <longdescription>display-gamma applied to the linear raw before feature detection, to lift shadow detail into the detector's range.\n1.0 disables it. higher values help under-exposed frames but can amplify shadow noise; the percentile stretch already does part of this, so the effect is scene-dependent.</longdescription>
+  </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_clahe_clip</name>
+    <type min="0.0" max="16.0">float</type>
+    <default>0.0</default>
+    <shortdescription>local contrast for feature detection (CLAHE clip)</shortdescription>
+    <longdescription>clip limit of the local contrast enhancement (CLAHE) applied before feature detection. 0 disables it.\nenabling it (e.g. 2.0) helps detect features on extremely under-exposed frames, but on repetitive textures (façades, railings, foliage) it can change descriptor signatures between exposures and cause mis-alignment, so it is off by default.</longdescription>
+  </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_sift_keypoints</name>
+    <type min="500" max="20000">int</type>
+    <default>5000</default>
+    <shortdescription>feature budget per frame (keypoints)</shortdescription>
+    <longdescription>maximum number of SIFT keypoints kept per frame after spatial balancing, before matching.\nbalancing both frames to a common budget keeps a feature-dense frame from flooding the matcher with ambiguous candidates.</longdescription>
+  </dtconfig>
+  <dtconfig prefs="processing" section="hdr_alignment">
+    <name>plugins/lighttable/hdr_merge_debug_images</name>
+    <type>bool</type>
+    <default>false</default>
+    <shortdescription>save alignment debug images</shortdescription>
+    <longdescription>write per-frame diagnostic images while merging: the feature-detection input, the detected keypoints and all feature matches (green = inlier, red = outlier).\nsaved as Netpbm (.pgm/.ppm) in a darktable_hdr_align_debug folder in the system temp directory (or the folder named by the DT_HDR_DEBUG_IMAGE_DIR environment variable). for diagnosing alignment problems; off by default.</longdescription>
+  </dtconfig>
   <dtconfig dialog="collect">
     <name>plugins/lighttable/tagging/case_sensitivity</name>
     <type>