From dc0a276edce12d9d813d9efd5b106fa848059520 Mon Sep 17 00:00:00 2001
From: Murat Raimbekov <raimbekov_m@auca.kg>
Date: Wed, 11 Feb 2026 18:06:26 +0600
Subject: [PATCH] Merge pull request #28324 from
 raimbekovm:fix-kaze-charbonnier

features2d: add missing KAZE DIFF_CHARBONNIER support #28324

### Description

This PR fixes the missing implementation for `DIFF_CHARBONNIER` diffusivity type in KAZE feature detector.

### Changes
- Added `charbonnier_diffusivity()` call for `DIFF_CHARBONNIER` type in `Create_Nonlinear_Scale_Space()`
- Added proper error handling for unsupported diffusivity types

### Problem
When using KAZE with `DIFF_CHARBONNIER` diffusivity type, keypoint coordinates were not computed at subpixel level, because the code lacked the specific handling for this diffusivity mode.

### Solution
The `charbonnier_diffusivity()` function already exists in `nldiffusion_functions.cpp`, it just wasn't being called. This PR adds the missing `else if` branch to call it, matching the pattern already implemented in `AKAZEFeatures.cpp`.

Fixes #27134

### Pull Request Readiness Checklist

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another copyleft license.
- [x] The PR is proposed to the proper branch.
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
- [ ] The feature is well documented and sample code can be built with the project CMake
---
 modules/features2d/src/kaze/KAZEFeatures.cpp |  4 ++
 modules/features2d/test/test_akaze.cpp       | 41 ++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/modules/features2d/src/kaze/KAZEFeatures.cpp b/modules/features2d/src/kaze/KAZEFeatures.cpp
index 72327e8683..30e0390359 100644
--- a/modules/features2d/src/kaze/KAZEFeatures.cpp
+++ b/modules/features2d/src/kaze/KAZEFeatures.cpp
@@ -128,6 +128,10 @@ int KAZEFeatures::Create_Nonlinear_Scale_Space(const Mat &img)
             pm_g2(evolution_[i].Lx, evolution_[i].Ly, Lflow, options_.kcontrast);
         else if (options_.diffusivity == KAZE::DIFF_WEICKERT)
             weickert_diffusivity(evolution_[i].Lx, evolution_[i].Ly, Lflow, options_.kcontrast);
+        else if (options_.diffusivity == KAZE::DIFF_CHARBONNIER)
+            charbonnier_diffusivity(evolution_[i].Lx, evolution_[i].Ly, Lflow, options_.kcontrast);
+        else
+            CV_Error_(Error::StsError, ("Diffusivity is not supported: %d", static_cast<int>(options_.diffusivity)));
 
         // Perform FED n inner steps
         for (int j = 0; j < nsteps_[i - 1]; j++)
diff --git a/modules/features2d/test/test_akaze.cpp b/modules/features2d/test/test_akaze.cpp
index aafa8a7545..e24894129a 100644
--- a/modules/features2d/test/test_akaze.cpp
+++ b/modules/features2d/test/test_akaze.cpp
@@ -45,4 +45,45 @@ TEST(Features2d_AKAZE, uninitialized_and_nans)
     akaze->detectAndCompute(b1, noArray(), keypoints, desc);
 }
 
+// Test for https://github.com/opencv/opencv/issues/27134
+TEST(Features2d_KAZE, diffusivity_charbonnier)
+{
+    Mat testImg(200, 200, CV_8U);
+    RNG rng(42);
+    rng.fill(testImg, RNG::UNIFORM, Scalar(0), Scalar(255), true);
+
+    // KAZE with DIFF_CHARBONNIER
+    Ptr<KAZE> kaze_charbonnier = KAZE::create(false, false, 0.001f, 4, 4, KAZE::DIFF_CHARBONNIER);
+    vector<KeyPoint> kps_charbonnier;
+    Mat desc_charbonnier;
+    kaze_charbonnier->detectAndCompute(testImg, noArray(), kps_charbonnier, desc_charbonnier);
+
+    // KAZE with DIFF_PM_G2 (default)
+    Ptr<KAZE> kaze_pm_g2 = KAZE::create(false, false, 0.001f, 4, 4, KAZE::DIFF_PM_G2);
+    vector<KeyPoint> kps_pm_g2;
+    Mat desc_pm_g2;
+    kaze_pm_g2->detectAndCompute(testImg, noArray(), kps_pm_g2, desc_pm_g2);
+
+    // Both should detect keypoints
+    ASSERT_FALSE(kps_charbonnier.empty());
+    ASSERT_FALSE(kps_pm_g2.empty());
+
+    // Check subpixel accuracy for DIFF_CHARBONNIER (issue #27134)
+    bool hasSubpixel = false;
+    for (size_t i = 0; i < kps_charbonnier.size(); i++)
+    {
+        float fx = kps_charbonnier[i].pt.x - std::floor(kps_charbonnier[i].pt.x);
+        float fy = kps_charbonnier[i].pt.y - std::floor(kps_charbonnier[i].pt.y);
+        if (fx > 1e-5f || fy > 1e-5f)
+        {
+            hasSubpixel = true;
+            break;
+        }
+    }
+    EXPECT_TRUE(hasSubpixel) << "KAZE with DIFF_CHARBONNIER should have subpixel keypoint coordinates";
+
+    // Descriptor dimensions should match
+    ASSERT_EQ(desc_charbonnier.cols, desc_pm_g2.cols);
+}
+
 }} // namespace