Small refactor on ImageComparison utils. (#7133)

* Small refactor on ImageComparison utils.

Signed-off-by: hershey5045 <43485729+hershey5045@users.noreply.github.com>

* Add aznumeric cast.

Signed-off-by: hershey5045 <43485729+hershey5045@users.noreply.github.com>

* Correction on aznumeric cast.

Signed-off-by: hershey5045 <43485729+hershey5045@users.noreply.github.com>

* Add unit test for new image comparison function.

Signed-off-by: hershey5045 <43485729+hershey5045@users.noreply.github.com>

Gems/Atom/Utils/Code/Include/Atom/Utils/ImageComparison.h

@@ -23,6 +23,9 @@ namespace AZ
             UnsupportedFormat
         };
 
+        //! Calculates the maximum difference of the rgb channels between two image buffers.
+        int16_t CalcMaxChannelDifference(AZStd::array_view<uint8_t> bufferA, AZStd::array_view<uint8_t> bufferB, size_t index);
+
         //! Compares two images and returns the RMS (root mean square) of the difference.
         //! @param buffer[A|B] the raw buffer of image data
         //! @param size[A|B] the dimensions of the image in the buffer

Gems/Atom/Utils/Code/Source/ImageComparison.cpp

@@ -14,6 +14,16 @@ namespace AZ
 {
     namespace Utils
     {
+        int16_t CalcMaxChannelDifference(AZStd::array_view<uint8_t> bufferA, AZStd::array_view<uint8_t> bufferB, size_t index)
+        {
+            // We use the max error from a single channel instead of accumulating the error from each channel.
+            // This normalizes differences so that for example black vs red has the same weight as black vs yellow.
+            const int16_t diffR = static_cast<int16_t>(abs(aznumeric_cast<int16_t>(bufferA[index]) - aznumeric_cast<int16_t>(bufferB[index])));
+            const int16_t diffG = static_cast<int16_t>(abs(aznumeric_cast<int16_t>(bufferA[index + 1]) - aznumeric_cast<int16_t>(bufferB[index + 1])));
+            const int16_t diffB = static_cast<int16_t>(abs(aznumeric_cast<int16_t>(bufferA[index + 2]) - aznumeric_cast<int16_t>(bufferB[index + 2])));
+            return AZ::GetMax(AZ::GetMax(diffR, diffG), diffB);
+        }
+
         ImageDiffResultCode CalcImageDiffRms(
             AZStd::span<const uint8_t> bufferA, const RHI::Size& sizeA, RHI::Format formatA,
             AZStd::span<const uint8_t> bufferB, const RHI::Size& sizeB, RHI::Format formatB,
@@ -67,14 +77,7 @@ namespace AZ
 
             for (size_t i = 0; i < bufferA.size(); i += BytesPerPixel)
             {
-                // We use the max error from a single channel instead of accumulating the error from each channel.
-                // This normalizes differences so that for example black vs red has the same weight as black vs yellow.
-                const int16_t diffR = static_cast<int16_t>(abs(aznumeric_cast<int16_t>(bufferA[i]) - aznumeric_cast<int16_t>(bufferB[i])));
-                const int16_t diffG = static_cast<int16_t>(abs(aznumeric_cast<int16_t>(bufferA[i + 1]) - aznumeric_cast<int16_t>(bufferB[i + 1])));
-                const int16_t diffB = static_cast<int16_t>(abs(aznumeric_cast<int16_t>(bufferA[i + 2]) - aznumeric_cast<int16_t>(bufferB[i + 2])));
-                const int16_t maxDiff = AZ::GetMax(AZ::GetMax(diffR, diffG), diffB);
-
-                const float finalDiffNormalized = maxDiff / 255.0f;
+                const float finalDiffNormalized = aznumeric_cast<float>(CalcMaxChannelDifference(bufferA, bufferB, i)) / 255.0f;
                 const float squared = finalDiffNormalized * finalDiffNormalized;
 
                 if (diffScore)

Gems/Atom/Utils/Code/Tests/ImageComparisonTests.cpp

@@ -127,6 +127,16 @@ namespace UnitTest
         EXPECT_EQ(0.0f, diffScore);
     }
 
+    
+    TEST_F(ImageComparisonTests, CheckMaxChannelDifference)
+    {
+        const AZStd::vector<uint8_t> imageA = { 255, 255, 255 };
+        const AZStd::vector<uint8_t> imageB = { 0, 125, 255 };
+        const int16_t maxChannelDiff = 255;
+        const int16_t res = CalcMaxChannelDifference(imageA, imageB, 0);
+        EXPECT_EQ(res, maxChannelDiff);
+    }
+
     TEST_F(ImageComparisonTests, CheckThreshold_SmallImagesWithDifferences)
     {
         AZ::RHI::Size size{2, 2, 1};