From fbde4f32fd501542d99e59c639d3f1154174240e Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Thu, 18 Oct 2018 17:04:41 +0100
Subject: [PATCH] Use scaled luminance trns comparison.

---
 .../Formats/Png/PngScanlineProcessor.cs           |   6 ++++--
 .../Formats/Png/PngDecoderTests.cs                |   3 ++-
 tests/ImageSharp.Tests/TestImages.cs              |   1 +
 tests/Images/Input/Png/gray-1-trns.png            | Bin 0 -> 366 bytes
 4 files changed, 7 insertions(+), 3 deletions(-)
 create mode 100644 tests/Images/Input/Png/gray-1-trns.png

diff --git a/src/ImageSharp/Formats/Png/PngScanlineProcessor.cs b/src/ImageSharp/Formats/Png/PngScanlineProcessor.cs
index 6c81ba76c2..5ea25e72d4 100644
--- a/src/ImageSharp/Formats/Png/PngScanlineProcessor.cs
+++ b/src/ImageSharp/Formats/Png/PngScanlineProcessor.cs
@@ -80,6 +80,7 @@ namespace SixLabors.ImageSharp.Formats.Png
             }
             else
             {
+                byte scaledLuminanceTrans = (byte)(luminanceTrans * scaleFactor);
                 Rgba32 rgba32 = default;
                 for (int x = 0; x < header.Width; x++)
                 {
@@ -87,7 +88,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                     rgba32.R = luminance;
                     rgba32.G = luminance;
                     rgba32.B = luminance;
-                    rgba32.A = luminance.Equals(luminanceTrans) ? byte.MinValue : byte.MaxValue;
+                    rgba32.A = luminance.Equals(scaledLuminanceTrans) ? byte.MinValue : byte.MaxValue;
 
                     pixel.PackFromRgba32(rgba32);
                     Unsafe.Add(ref rowSpanRef, x) = pixel;
@@ -163,6 +164,7 @@ namespace SixLabors.ImageSharp.Formats.Png
             }
             else
             {
+                byte scaledLuminanceTrans = (byte)(luminanceTrans * scaleFactor);
                 Rgba32 rgba32 = default;
                 for (int x = pixelOffset; x < header.Width; x += increment)
                 {
@@ -170,7 +172,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                     rgba32.R = luminance;
                     rgba32.G = luminance;
                     rgba32.B = luminance;
-                    rgba32.A = luminance.Equals(luminanceTrans) ? byte.MinValue : byte.MaxValue;
+                    rgba32.A = luminance.Equals(scaledLuminanceTrans) ? byte.MinValue : byte.MaxValue;
 
                     pixel.PackFromRgba32(rgba32);
                     Unsafe.Add(ref rowSpanRef, x) = pixel;
diff --git a/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs b/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs
index 54f3e397c3..f51f9b6c5c 100644
--- a/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs
+++ b/tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs
@@ -40,7 +40,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
             TestImages.Png.VimImage2,
 
             TestImages.Png.Rgb24BppTrans,
-            TestImages.Png.GrayAlpha8Bit
+            TestImages.Png.GrayAlpha8Bit,
+            TestImages.Png.Gray1BitTrans
         };
 
         public static readonly string[] TestImages48Bpp =
diff --git a/tests/ImageSharp.Tests/TestImages.cs b/tests/ImageSharp.Tests/TestImages.cs
index fdf586c430..758f256345 100644
--- a/tests/ImageSharp.Tests/TestImages.cs
+++ b/tests/ImageSharp.Tests/TestImages.cs
@@ -45,6 +45,7 @@ namespace SixLabors.ImageSharp.Tests
             public const string Kaboom = "Png/kaboom.png";
             public const string PDSrc = "Png/pd-source.png";
             public const string PDDest = "Png/pd-dest.png";
+            public const string Gray1BitTrans = "Png/gray-1-trns.png";
 
             // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
             public const string Filter0 = "Png/filter0.png";
diff --git a/tests/Images/Input/Png/gray-1-trns.png b/tests/Images/Input/Png/gray-1-trns.png
new file mode 100644
index 0000000000000000000000000000000000000000..99b288d52666f930ba760226e0687fd16c18e967
GIT binary patch
literal 366
zcmeAS@N?(olHy`uVBq!ia0y~yVAN$`VCrH73NSci8gu|Drjj7PU<O9UDSy`id7K3v
zk;OpT1B~5HX4?T78$4YcLn>~)y|GZ}kOL3P1p|(h`kCj~HI)TOcnDs2`|;Yn&D&2d
zc^7STeg3AM*X9_!nQ1%k9^2s!>o-0rI$*$ac*DU6>$&Pc+F)ADDv7q<!@In8B}lX-
zO0>N_Jt<t1$69Z<nfwMdpn~{~PqrNa>VTp*E8bj_Ra<oqtQM#ojHaEL^gbWRj?jC(
zoChp)W1UXr)I&f$cB$)|5+847?b~tgk7(O!C!pI^OI#yLQW8s2t&)pUffR$0fuV)2
zp@FWUMTmigm64^DfuXK}iIsst@I4J#6b-rgDVb@NxHTv>Pgn@lz~JfX=d#Wzp$Pzp
C@PiTn

literal 0
HcmV?d00001