Remove invalid Subsampling checks.

src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegComponent.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -22,11 +22,8 @@ public JpegComponent(MemoryAllocator memoryAllocator, JpegFrame frame, byte id,
             this.Frame = frame;
             this.Id = id;
 
-            // Valid sampling factors are 1..2
-            if (horizontalFactor == 0
-                || verticalFactor == 0
-                || horizontalFactor > 2
-                || verticalFactor > 2)
+            // Validate sampling factors.
+            if (horizontalFactor == 0 || verticalFactor == 0)
             {
                 JpegThrowHelper.ThrowBadSampling();
             }
@@ -138,4 +135,4 @@ public void Init()
             this.SpectralBlocks = this.memoryAllocator.Allocate2D<Block8x8>(width, height, AllocationOptions.Clean);
         }
     }
-}
+}

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -764,7 +764,7 @@ private void ProcessStartOfFrameMarker(int remaining, in JpegFileMarker frameMar
                 for (int i = 0; i < this.ComponentCount; i++)
                 {
                     byte hv = this.temp[index + 1];
-                    int h = hv >> 4;
+                    int h = (hv >> 4) & 15;
                     int v = hv & 15;
 
                     if (maxH < h)

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Images.cs

@@ -31,13 +31,17 @@ public partial class JpegDecoderTests
                 TestImages.Jpeg.Issues.InvalidAPP0721,
                 TestImages.Jpeg.Issues.ExifGetString750Load,
                 TestImages.Jpeg.Issues.ExifGetString750Transform,
+                TestImages.Jpeg.Issues.BadSubSampling1076,
 
                 // LibJpeg can open this despite the invalid density units.
                 TestImages.Jpeg.Issues.Fuzz.ArgumentOutOfRangeException825B,
 
                 // LibJpeg can open this despite incorrect colorspace metadata.
                 TestImages.Jpeg.Issues.IncorrectColorspace855,
 
+                // LibJpeg can open this despite the invalid subsampling units.
+                TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824C,
+
                 // High depth images
                 TestImages.Jpeg.Baseline.Testorig12bit,
             };
@@ -71,7 +75,6 @@ public partial class JpegDecoderTests
             TestImages.Jpeg.Issues.Fuzz.NullReferenceException823,
             TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824A,
             TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824B,
-            TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824C,
             TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824D,
             TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824E,
             TestImages.Jpeg.Issues.Fuzz.IndexOutOfRangeException824F,

tests/ImageSharp.Tests/TestImages.cs

@@ -192,6 +192,7 @@ public static class Issues
                 public const string IncorrectColorspace855 = "Jpg/issues/issue855-incorrect-colorspace.jpg";
                 public const string IncorrectResize1006 = "Jpg/issues/issue1006-incorrect-resize.jpg";
                 public const string ExifResize1049 = "Jpg/issues/issue1049-exif-resize.jpg";
+                public const string BadSubSampling1076 = "Jpg/issues/issue-1076-invalid-subsampling.jpg";
 
                 public static class Fuzz
                 {