From ea8fccc76d8c3f8f3860ffda87fb8a044b59aa65 Mon Sep 17 00:00:00 2001
From: Michael Migliore <mcmigliore@gmail.com>
Date: Fri, 3 Jan 2025 14:55:36 +0100
Subject: [PATCH 1/5] Refactor image::compare

---
 application/F3DStarter.cxx                 |  2 +-
 examples/libf3d/cpp/render-image/check.cxx |  3 +-
 examples/libf3d/python/img-cmp/img-cmp.py  |  4 +-
 library/public/image.h                     | 11 ++----
 library/src/image.cxx                      | 43 +++++-----------------
 library/testing/TestSDKHelpers.h           |  5 ++-
 library/testing/TestSDKImage.cxx           | 41 ++++++---------------
 python/testing/test_image_compare.py       |  2 +-
 python/testing/test_scene.py               |  4 +-
 9 files changed, 34 insertions(+), 81 deletions(-)

diff --git a/application/F3DStarter.cxx b/application/F3DStarter.cxx
index a8739c5409..f2ea681015 100644
--- a/application/F3DStarter.cxx
+++ b/application/F3DStarter.cxx
@@ -1025,7 +1025,7 @@ int F3DStarter::Start(int argc, char** argv)
       f3d::image diff;
       double error;
       const double& threshold = this->Internals->AppOptions.RefThreshold;
-      if (!img.compare(ref, threshold, error))
+      if (img.compare(ref) > threshold)
       {
         if (output.empty())
         {
diff --git a/examples/libf3d/cpp/render-image/check.cxx b/examples/libf3d/cpp/render-image/check.cxx
index 1fe8284f81..c5f72d85f5 100644
--- a/examples/libf3d/cpp/render-image/check.cxx
+++ b/examples/libf3d/cpp/render-image/check.cxx
@@ -13,6 +13,5 @@ int main(int argc, char** argv)
   f3d::image img1(argv[2]);
 
   // Compare them
-  double error;
-  return img0.compare(img1, 0.05, error) ? EXIT_SUCCESS : EXIT_FAILURE;
+  return img0.compare(img1) <= 0.05 ? EXIT_SUCCESS : EXIT_FAILURE;
 }
diff --git a/examples/libf3d/python/img-cmp/img-cmp.py b/examples/libf3d/python/img-cmp/img-cmp.py
index 093abdcb2a..58b82fb5d2 100644
--- a/examples/libf3d/python/img-cmp/img-cmp.py
+++ b/examples/libf3d/python/img-cmp/img-cmp.py
@@ -11,9 +11,7 @@
     diff = f3d.Image()
     error = 0.0
 
-    result = img_0.compare(img_1, 0.05, diff, error)
-
-    if result:
+    if img_0.compare(img_1) <= 0.05:
         print("Images are identical")
     else:
         print("Images are different")
diff --git a/library/public/image.h b/library/public/image.h
index 1165c5a504..dddaab8b82 100644
--- a/library/public/image.h
+++ b/library/public/image.h
@@ -135,23 +135,20 @@ class F3D_EXPORT image
   ///@}
 
   /**
-   * Compare current image to a reference using the provided threshold.
-   * If the comparison fails, ie. error is higher than the threshold,
-   * this outputs the resulting diff and error and return false,
-   * return true otherwise.
+   * Compare current image to a reference.
    * The error is minimum between Minkownski and Wasserstein distance
    * on a SSIM computation, as specified in VTK.
    * Please note, due to possible arithmetic imprecision in the SSIM computation
-   * using a threshold of zero may return false with identical images.
+   * a non-zero value can be returned with identical images.
    * Depending on the VTK version, another comparison algorithm may be used.
-   * Threshold should be in range [0, 1[, this returns false otherwise.
+   * Error value meaning is described below:
    * 1e-14: Pixel perfect comparison.
    * 0.04: Visually indistinguishable.
    * 0.1: Small visible difference.
    * 0.5: Comparable images.
    * 1.0: Different type, size or number of components
    */
-  bool compare(const image& reference, double threshold, double& error) const;
+  double compare(const image& reference) const;
 
   /**
    * Save an image to the provided file path, used as is, in the specified format.
diff --git a/library/src/image.cxx b/library/src/image.cxx
index c0a68d199d..9fc2bfc4cc 100644
--- a/library/src/image.cxx
+++ b/library/src/image.cxx
@@ -344,39 +344,28 @@ void* image::getContent() const
 }
 
 //----------------------------------------------------------------------------
-bool image::compare(const image& reference, double threshold, double& error) const
+double image::compare(const image& reference) const
 {
-  // Sanity check for threshold
-  if (threshold < 0 || threshold >= 1)
-  {
-    error = 1;
-    return false;
-  }
-
   ChannelType type = this->getChannelType();
   if (type != reference.getChannelType())
   {
-    error = 1;
-    return false;
+    return 1.0;
   }
 
   unsigned int count = this->getChannelCount();
   if (count != reference.getChannelCount())
   {
-    error = 1;
-    return false;
+    return 1.0;
   }
 
   if (this->getWidth() != reference.getWidth() || this->getHeight() != reference.getHeight())
   {
-    error = 1;
-    return false;
+    return 1.0;
   }
 
   if (this->getWidth() == 0 && this->getHeight() == 0)
   {
-    error = 0;
-    return true;
+    return 0.0;
   }
 
 #if VTK_VERSION_NUMBER >= VTK_VERSION_CHECK(9, 3, 20240729)
@@ -406,39 +395,27 @@ bool image::compare(const image& reference, double threshold, double& error) con
   // Thanks to the checks above, this is always true
   assert(scalars != nullptr);
 
-  double unused;
+  double error, unused;
   vtkImageSSIM::ComputeErrorMetrics(scalars, error, unused);
-  return error <= threshold;
+  return error;
 #else
-  threshold *= 1000;
-
   vtkNew<vtkImageDifference> imDiff;
   imDiff->SetThreshold(0);
   imDiff->SetInputData(this->Internals->Image);
   imDiff->SetImageData(reference.Internals->Image);
   imDiff->UpdateInformation();
-  error = imDiff->GetThresholdedError();
-
-  if (error <= threshold)
-  {
-    imDiff->Update();
-    error = imDiff->GetThresholdedError();
-  }
-
-  bool ret = error <= threshold;
-  error /= 1000;
-  return ret;
+  double error = imDiff->GetThresholdedError();
+  return error / 1000.0;
 #endif
 }
 
 //----------------------------------------------------------------------------
 bool image::operator==(const image& reference) const
 {
-  double error;
   // XXX: We do not use 0 because even with identical images, rounding error, arithmetic imprecision
   // or architecture issue may cause the value to not be 0. See:
   // https://develop.openfoam.com/Development/openfoam/-/issues/2958
-  return this->compare(reference, 1e-14, error);
+  return this->compare(reference) <= 1e-14;
 }
 
 //----------------------------------------------------------------------------
diff --git a/library/testing/TestSDKHelpers.h b/library/testing/TestSDKHelpers.h
index f156bb7b87..09980dd224 100644
--- a/library/testing/TestSDKHelpers.h
+++ b/library/testing/TestSDKHelpers.h
@@ -35,9 +35,10 @@ static bool RenderTest(const f3d::image& img, const std::string& baselinePath,
   }
 
   f3d::image reference(baseline);
-  double error;
 
-  if (!img.compare(reference, threshold, error))
+  double error = img.compare(reference);
+
+  if (error > threshold)
   {
     std::cerr << "Current rendering difference with reference image " << baseline << " : " << error
               << " is higher than the threshold of " << threshold << std::endl;
diff --git a/library/testing/TestSDKImage.cxx b/library/testing/TestSDKImage.cxx
index 6cbc7554b2..7b022de275 100644
--- a/library/testing/TestSDKImage.cxx
+++ b/library/testing/TestSDKImage.cxx
@@ -139,10 +139,7 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baseline(testingDir + "/baselines/TestSDKImage.png");
   if (generated != baseline)
   {
-    double error;
-    generated.compare(baseline, 0, error);
-
-    std::cerr << "Generated image is different from the png baseline: " << error << std::endl;
+    std::cerr << "Generated image is different from the png baseline: " << generated.compare(baseline) << std::endl;
     return EXIT_FAILURE;
   }
 
@@ -151,10 +148,7 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baselineTIF(testingDir + "/baselines/TestSDKImage.tif");
   if (generated != baselineTIF)
   {
-    double error;
-    generated.compare(baselineTIF, 0, error);
-
-    std::cerr << "Generated image is different from the tif baseline: " << error << std::endl;
+    std::cerr << "Generated image is different from the tif baseline: " << generated.compare(baselineTIF) << std::endl;
     return EXIT_FAILURE;
   }*/
 
@@ -171,10 +165,7 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baseline16(testingDir + "/baselines/TestSDKImage16.png");
   if (generated16 != baseline16)
   {
-    double error;
-    generated16.compare(baseline16, 0, error);
-
-    std::cerr << "generated short image is different from the baseline: " << error << std::endl;
+    std::cerr << "generated short image is different from the baseline: " << generated16.compare(baseline16) << std::endl;
     return EXIT_FAILURE;
   }
 
@@ -183,10 +174,7 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baseline16TIF(testingDir + "/baselines/TestSDKImage16.tif");
   if (generated16 != baseline16TIF)
   {
-    double error;
-    generated16.compare(baseline16TIF, 0, error);
-
-    std::cerr << "generated short image is different from the TIF baseline: " << error << std::endl;
+    std::cerr << "generated short image is different from the TIF baseline: " << generated16.compare(baseline16TIF) << std::endl;
     return EXIT_FAILURE;
   }*/
 
@@ -204,10 +192,7 @@ int TestSDKImage(int argc, char* argv[])
 
   if (generated32 != baseline32)
   {
-    double error;
-    generated32.compare(baseline32, 0, error);
-
-    std::cerr << "generated float image is different from the baseline: " << error << std::endl;
+    std::cerr << "generated float image is different from the baseline: " << generated32.compare(baseline32) << std::endl;
     return EXIT_FAILURE;
   }
 #endif // F3D_SSIM_COMPARE
@@ -300,22 +285,18 @@ int TestSDKImage(int argc, char* argv[])
   }
 
   // Test image::compare dedicated code paths
-  double error;
-  test("compare images with different channel types",
-    !generated.compare(generated16, 0, error) && error == 1.);
+  test("compare images with different channel types", generated.compare(generated16) == 1.);
 
   f3d::image generatedCount(width, height, channels + 1);
-  test("compare images with different channel count",
-    !generated.compare(generatedCount, 0, error) && error == 1.);
+  test("compare images with different channel count", generated.compare(generatedCount) == 1.);
 
   f3d::image generatedSize(width + 1, height, channels);
-  test("compare images with different size",
-    !generated.compare(generatedSize, 0, error) && error == 1.);
+  test("compare images with different size", generated.compare(generatedSize) == 1.);
 
   f3d::image empty(0, 0, 0);
-  test("compare empty images", empty.compare(empty, 0, error) && error == 0.);
-  test("compare with negative threshold", !empty.compare(empty, -1, error) && error == 1.);
-  test("compare with threshold == 1", !empty.compare(empty, 1, error) && error == 1.);
+  test("compare empty images", empty.compare(empty) == 0.);
+  test("compare with negative threshold", empty.compare(empty) == 1.);
+  test("compare with threshold == 1", empty.compare(empty) == 1.);
 
   return test.result();
 }
diff --git a/python/testing/test_image_compare.py b/python/testing/test_image_compare.py
index e7fa2cf87b..f3d85e0209 100644
--- a/python/testing/test_image_compare.py
+++ b/python/testing/test_image_compare.py
@@ -26,4 +26,4 @@ def test_compare_with_file():
 
     error = 0.0
 
-    assert img.compare(f3d.Image(reference), 0.05, error)
+    assert img.compare(f3d.Image(reference)) <= 0.05
diff --git a/python/testing/test_scene.py b/python/testing/test_scene.py
index f28e6d0f72..cd69f22670 100644
--- a/python/testing/test_scene.py
+++ b/python/testing/test_scene.py
@@ -26,7 +26,7 @@ def test_scene_memory():
 
     error = 0.0
 
-    assert img.compare(f3d.Image(reference), 0.05, error)
+    assert img.compare(f3d.Image(reference)) < 0.05
 
 
 def test_scene():
@@ -54,4 +54,4 @@ def test_scene():
 
     error = 0.0
 
-    assert img.compare(f3d.Image(reference), 0.05, error)
+    assert img.compare(f3d.Image(reference)) < 0.05

From b76a66710655c8bb473219648c82d9079feb5af1 Mon Sep 17 00:00:00 2001
From: Michael Migliore <mcmigliore@gmail.com>
Date: Fri, 3 Jan 2025 14:57:57 +0100
Subject: [PATCH 2/5] format

---
 library/testing/TestSDKImage.cxx | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/library/testing/TestSDKImage.cxx b/library/testing/TestSDKImage.cxx
index 7b022de275..85efc9a61d 100644
--- a/library/testing/TestSDKImage.cxx
+++ b/library/testing/TestSDKImage.cxx
@@ -139,7 +139,8 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baseline(testingDir + "/baselines/TestSDKImage.png");
   if (generated != baseline)
   {
-    std::cerr << "Generated image is different from the png baseline: " << generated.compare(baseline) << std::endl;
+    std::cerr << "Generated image is different from the png baseline: "
+              << generated.compare(baseline) << std::endl;
     return EXIT_FAILURE;
   }
 
@@ -148,7 +149,8 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baselineTIF(testingDir + "/baselines/TestSDKImage.tif");
   if (generated != baselineTIF)
   {
-    std::cerr << "Generated image is different from the tif baseline: " << generated.compare(baselineTIF) << std::endl;
+    std::cerr << "Generated image is different from the tif baseline: "
+              << generated.compare(baselineTIF) << std::endl;
     return EXIT_FAILURE;
   }*/
 
@@ -165,7 +167,8 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baseline16(testingDir + "/baselines/TestSDKImage16.png");
   if (generated16 != baseline16)
   {
-    std::cerr << "generated short image is different from the baseline: " << generated16.compare(baseline16) << std::endl;
+    std::cerr << "generated short image is different from the baseline: "
+              << generated16.compare(baseline16) << std::endl;
     return EXIT_FAILURE;
   }
 
@@ -174,7 +177,8 @@ int TestSDKImage(int argc, char* argv[])
   f3d::image baseline16TIF(testingDir + "/baselines/TestSDKImage16.tif");
   if (generated16 != baseline16TIF)
   {
-    std::cerr << "generated short image is different from the TIF baseline: " << generated16.compare(baseline16TIF) << std::endl;
+    std::cerr << "generated short image is different from the TIF baseline: "
+              << generated16.compare(baseline16TIF) << std::endl;
     return EXIT_FAILURE;
   }*/
 
@@ -192,7 +196,8 @@ int TestSDKImage(int argc, char* argv[])
 
   if (generated32 != baseline32)
   {
-    std::cerr << "generated float image is different from the baseline: " << generated32.compare(baseline32) << std::endl;
+    std::cerr << "generated float image is different from the baseline: "
+              << generated32.compare(baseline32) << std::endl;
     return EXIT_FAILURE;
   }
 #endif // F3D_SSIM_COMPARE

From 551c28a60c3d73117bcccb6df2ac3e98155bff13 Mon Sep 17 00:00:00 2001
From: Michael Migliore <mcmigliore@gmail.com>
Date: Fri, 3 Jan 2025 15:10:19 +0100
Subject: [PATCH 3/5] fix

---
 application/F3DStarter.cxx | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/application/F3DStarter.cxx b/application/F3DStarter.cxx
index f2ea681015..5ef2b704b6 100644
--- a/application/F3DStarter.cxx
+++ b/application/F3DStarter.cxx
@@ -1023,9 +1023,9 @@ int F3DStarter::Start(int argc, char** argv)
       f3d::image img = window.renderToImage(this->Internals->AppOptions.NoBackground);
       f3d::image ref(reference);
       f3d::image diff;
-      double error;
+      double error = img.compare(ref);
       const double& threshold = this->Internals->AppOptions.RefThreshold;
-      if (img.compare(ref) > threshold)
+      if (error > threshold)
       {
         if (output.empty())
         {

From 550572e5634b6c9c62dc3f3f171a1bef21142b7b Mon Sep 17 00:00:00 2001
From: Michael Migliore <mcmigliore@gmail.com>
Date: Fri, 3 Jan 2025 16:11:23 +0100
Subject: [PATCH 4/5] fix

---
 library/testing/TestSDKImage.cxx | 2 --
 1 file changed, 2 deletions(-)

diff --git a/library/testing/TestSDKImage.cxx b/library/testing/TestSDKImage.cxx
index 85efc9a61d..f7b7d7f558 100644
--- a/library/testing/TestSDKImage.cxx
+++ b/library/testing/TestSDKImage.cxx
@@ -300,8 +300,6 @@ int TestSDKImage(int argc, char* argv[])
 
   f3d::image empty(0, 0, 0);
   test("compare empty images", empty.compare(empty) == 0.);
-  test("compare with negative threshold", empty.compare(empty) == 1.);
-  test("compare with threshold == 1", empty.compare(empty) == 1.);
 
   return test.result();
 }

From 5450f0b0a1fe26a458f895f53bba988386e5c461 Mon Sep 17 00:00:00 2001
From: Michael Migliore <mcmigliore@gmail.com>
Date: Fri, 3 Jan 2025 16:49:00 +0100
Subject: [PATCH 5/5] fix

---
 library/src/image.cxx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/src/image.cxx b/library/src/image.cxx
index 9fc2bfc4cc..121b95d6c5 100644
--- a/library/src/image.cxx
+++ b/library/src/image.cxx
@@ -403,7 +403,7 @@ double image::compare(const image& reference) const
   imDiff->SetThreshold(0);
   imDiff->SetInputData(this->Internals->Image);
   imDiff->SetImageData(reference.Internals->Image);
-  imDiff->UpdateInformation();
+  imDiff->Update();
   double error = imDiff->GetThresholdedError();
   return error / 1000.0;
 #endif