Merge branch 'master' into bp/webpbenchmarks

src/ImageSharp/Color/Color.Conversions.cs

@@ -17,56 +17,118 @@ namespace SixLabors.ImageSharp
         /// </summary>
         /// <param name="pixel">The <see cref="Rgba64"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Rgba64 pixel) => this.data = pixel;
+        public Color(Rgba64 pixel)
+        {
+            this.data = pixel;
+            this.boxedHighPrecisionPixel = null;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Color"/> struct.
+        /// </summary>
+        /// <param name="pixel">The <see cref="Rgb48"/> containing the color information.</param>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public Color(Rgb48 pixel)
+        {
+            this.data = new Rgba64(pixel.R, pixel.G, pixel.B, ushort.MaxValue);
+            this.boxedHighPrecisionPixel = null;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Color"/> struct.
+        /// </summary>
+        /// <param name="pixel">The <see cref="La32"/> containing the color information.</param>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public Color(La32 pixel)
+        {
+            this.data = new Rgba64(pixel.L, pixel.L, pixel.L, pixel.A);
+            this.boxedHighPrecisionPixel = null;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Color"/> struct.
+        /// </summary>
+        /// <param name="pixel">The <see cref="L16"/> containing the color information.</param>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public Color(L16 pixel)
+        {
+            this.data = new Rgba64(pixel.PackedValue, pixel.PackedValue, pixel.PackedValue, ushort.MaxValue);
+            this.boxedHighPrecisionPixel = null;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Color"/> struct.
         /// </summary>
         /// <param name="pixel">The <see cref="Rgba32"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Rgba32 pixel) => this.data = new Rgba64(pixel);
+        public Color(Rgba32 pixel)
+        {
+            this.data = new Rgba64(pixel);
+            this.boxedHighPrecisionPixel = null;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Color"/> struct.
         /// </summary>
         /// <param name="pixel">The <see cref="Argb32"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Argb32 pixel) => this.data = new Rgba64(pixel);
+        public Color(Argb32 pixel)
+        {
+            this.data = new Rgba64(pixel);
+            this.boxedHighPrecisionPixel = null;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Color"/> struct.
         /// </summary>
         /// <param name="pixel">The <see cref="Bgra32"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Bgra32 pixel) => this.data = new Rgba64(pixel);
+        public Color(Bgra32 pixel)
+        {
+            this.data = new Rgba64(pixel);
+            this.boxedHighPrecisionPixel = null;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Color"/> struct.
         /// </summary>
         /// <param name="pixel">The <see cref="Rgb24"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Rgb24 pixel) => this.data = new Rgba64(pixel);
+        public Color(Rgb24 pixel)
+        {
+            this.data = new Rgba64(pixel);
+            this.boxedHighPrecisionPixel = null;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Color"/> struct.
         /// </summary>
         /// <param name="pixel">The <see cref="Bgr24"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Bgr24 pixel) => this.data = new Rgba64(pixel);
+        public Color(Bgr24 pixel)
+        {
+            this.data = new Rgba64(pixel);
+            this.boxedHighPrecisionPixel = null;
+        }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Color"/> struct.
         /// </summary>
         /// <param name="vector">The <see cref="Vector4"/> containing the color information.</param>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public Color(Vector4 vector) => this.data = new Rgba64(vector);
+        public Color(Vector4 vector)
+        {
+            vector = Numerics.Clamp(vector, Vector4.Zero, Vector4.One);
+            this.boxedHighPrecisionPixel = new RgbaVector(vector.X, vector.Y, vector.Z, vector.W);
+            this.data = default;
+        }
 
         /// <summary>
         /// Converts a <see cref="Color"/> to <see cref="Vector4"/>.
         /// </summary>
         /// <param name="color">The <see cref="Color"/>.</param>
         /// <returns>The <see cref="Vector4"/>.</returns>
-        public static explicit operator Vector4(Color color) => color.data.ToVector4();
+        public static explicit operator Vector4(Color color) => color.ToVector4();
 
         /// <summary>
         /// Converts an <see cref="Vector4"/> to <see cref="Color"/>.
@@ -74,24 +136,82 @@ namespace SixLabors.ImageSharp
         /// <param name="source">The <see cref="Vector4"/>.</param>
         /// <returns>The <see cref="Color"/>.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public static explicit operator Color(Vector4 source) => new Color(source);
+        public static explicit operator Color(Vector4 source) => new(source);
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal Rgba32 ToRgba32() => this.data.ToRgba32();
+        internal Rgba32 ToRgba32()
+        {
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.ToRgba32();
+            }
+
+            Rgba32 value = default;
+            this.boxedHighPrecisionPixel.ToRgba32(ref value);
+            return value;
+        }
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal Bgra32 ToBgra32() => this.data.ToBgra32();
+        internal Bgra32 ToBgra32()
+        {
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.ToBgra32();
+            }
+
+            Bgra32 value = default;
+            value.FromScaledVector4(this.boxedHighPrecisionPixel.ToScaledVector4());
+            return value;
+        }
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal Argb32 ToArgb32() => this.data.ToArgb32();
+        internal Argb32 ToArgb32()
+        {
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.ToArgb32();
+            }
+
+            Argb32 value = default;
+            value.FromScaledVector4(this.boxedHighPrecisionPixel.ToScaledVector4());
+            return value;
+        }
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal Rgb24 ToRgb24() => this.data.ToRgb24();
+        internal Rgb24 ToRgb24()
+        {
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.ToRgb24();
+            }
+
+            Rgb24 value = default;
+            value.FromScaledVector4(this.boxedHighPrecisionPixel.ToScaledVector4());
+            return value;
+        }
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal Bgr24 ToBgr24() => this.data.ToBgr24();
+        internal Bgr24 ToBgr24()
+        {
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.ToBgr24();
+            }
+
+            Bgr24 value = default;
+            value.FromScaledVector4(this.boxedHighPrecisionPixel.ToScaledVector4());
+            return value;
+        }
 
         [MethodImpl(InliningOptions.ShortMethod)]
-        internal Vector4 ToVector4() => this.data.ToVector4();
+        internal Vector4 ToVector4()
+        {
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.ToScaledVector4();
+            }
+
+            return this.boxedHighPrecisionPixel.ToScaledVector4();
+        }
     }
 }

src/ImageSharp/Color/Color.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Numerics;
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp
@@ -21,6 +20,7 @@ namespace SixLabors.ImageSharp
     public readonly partial struct Color : IEquatable<Color>
     {
         private readonly Rgba64 data;
+        private readonly IPixel boxedHighPrecisionPixel;
 
         [MethodImpl(InliningOptions.ShortMethod)]
         private Color(byte r, byte g, byte b, byte a)
@@ -30,6 +30,8 @@ namespace SixLabors.ImageSharp
                 ColorNumerics.UpscaleFrom8BitTo16Bit(g),
                 ColorNumerics.UpscaleFrom8BitTo16Bit(b),
                 ColorNumerics.UpscaleFrom8BitTo16Bit(a));
+
+            this.boxedHighPrecisionPixel = null;
         }
 
         [MethodImpl(InliningOptions.ShortMethod)]
@@ -40,6 +42,15 @@ namespace SixLabors.ImageSharp
                 ColorNumerics.UpscaleFrom8BitTo16Bit(g),
                 ColorNumerics.UpscaleFrom8BitTo16Bit(b),
                 ushort.MaxValue);
+
+            this.boxedHighPrecisionPixel = null;
+        }
+
+        [MethodImpl(InliningOptions.ShortMethod)]
+        private Color(IPixel pixel)
+        {
+            this.boxedHighPrecisionPixel = pixel;
+            this.data = default;
         }
 
         /// <summary>
@@ -52,13 +63,10 @@ namespace SixLabors.ImageSharp
         /// otherwise, false.
         /// </returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public static bool operator ==(Color left, Color right)
+        public static bool operator ==(Color left, Color right) => left.Equals(right);
-        {
-            return left.Equals(right);
-        }
 
         /// <summary>
-        /// Checks whether two <see cref="Color"/> structures are equal.
+        /// Checks whether two <see cref="Color"/> structures are not equal.
         /// </summary>
         /// <param name="left">The left hand <see cref="Color"/> operand.</param>
         /// <param name="right">The right hand <see cref="Color"/> operand.</param>
@@ -67,10 +75,7 @@ namespace SixLabors.ImageSharp
         /// otherwise, false.
         /// </returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public static bool operator !=(Color left, Color right)
+        public static bool operator !=(Color left, Color right) => !left.Equals(right);
-        {
-            return !left.Equals(right);
-        }
 
         /// <summary>
         /// Creates a <see cref="Color"/> from RGBA bytes.
@@ -81,7 +86,7 @@ namespace SixLabors.ImageSharp
         /// <param name="a">The alpha component (0-255).</param>
         /// <returns>The <see cref="Color"/>.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public static Color FromRgba(byte r, byte g, byte b, byte a) => new Color(r, g, b, a);
+        public static Color FromRgba(byte r, byte g, byte b, byte a) => new(r, g, b, a);
 
         /// <summary>
         /// Creates a <see cref="Color"/> from RGB bytes.
@@ -91,7 +96,46 @@ namespace SixLabors.ImageSharp
         /// <param name="b">The blue component (0-255).</param>
         /// <returns>The <see cref="Color"/>.</returns>
         [MethodImpl(InliningOptions.ShortMethod)]
-        public static Color FromRgb(byte r, byte g, byte b) => new Color(r, g, b);
+        public static Color FromRgb(byte r, byte g, byte b) => new(r, g, b);
+
+        /// <summary>
+        /// Creates a <see cref="Color"/> from the given <typeparamref name="TPixel"/>.
+        /// </summary>
+        /// <param name="pixel">The pixel to convert from.</param>
+        /// <typeparam name="TPixel">The pixel format.</typeparam>
+        /// <returns>The <see cref="Color"/>.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public static Color FromPixel<TPixel>(TPixel pixel)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            // Avoid boxing in case we can convert to Rgba64 safely and efficently
+            if (typeof(TPixel) == typeof(Rgba64))
+            {
+                return new((Rgba64)(object)pixel);
+            }
+            else if (typeof(TPixel) == typeof(Rgb48))
+            {
+                return new((Rgb48)(object)pixel);
+            }
+            else if (typeof(TPixel) == typeof(La32))
+            {
+                return new((La32)(object)pixel);
+            }
+            else if (typeof(TPixel) == typeof(L16))
+            {
+                return new((L16)(object)pixel);
+            }
+            else if (Unsafe.SizeOf<TPixel>() <= Unsafe.SizeOf<Rgba32>())
+            {
+                Rgba32 p = default;
+                pixel.ToRgba32(ref p);
+                return new(p);
+            }
+            else
+            {
+                return new(pixel);
+            }
+        }
 
         /// <summary>
         /// Creates a new instance of the <see cref="Color"/> struct
@@ -213,7 +257,7 @@ namespace SixLabors.ImageSharp
         public override string ToString() => this.ToHex();
 
         /// <summary>
-        /// Converts the color instance to a specified <see cref="IPixel{TSelf}"/> type.
+        /// Converts the color instance to a specified <typeparamref name="TPixel"/> type.
         /// </summary>
         /// <typeparam name="TPixel">The pixel type to convert to.</typeparam>
         /// <returns>The pixel value.</returns>
@@ -221,13 +265,18 @@ namespace SixLabors.ImageSharp
         public TPixel ToPixel<TPixel>()
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            TPixel pixel = default;
+            if (this.boxedHighPrecisionPixel is TPixel pixel)
+            {
+                return pixel;
+            }
+
+            pixel = default;
             pixel.FromRgba64(this.data);
             return pixel;
         }
 
         /// <summary>
-        /// Bulk converts a span of <see cref="Color"/> to a span of a specified <see cref="IPixel{TSelf}"/> type.
+        /// Bulk converts a span of <see cref="Color"/> to a span of a specified <typeparamref name="TPixel"/> type.
         /// </summary>
         /// <typeparam name="TPixel">The pixel type to convert to.</typeparam>
         /// <param name="configuration">The configuration.</param>
@@ -240,28 +289,38 @@ namespace SixLabors.ImageSharp
             Span<TPixel> destination)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            ReadOnlySpan<Rgba64> rgba64Span = MemoryMarshal.Cast<Color, Rgba64>(source);
+            Guard.DestinationShouldNotBeTooShort(source, destination, nameof(destination));
-            PixelOperations<TPixel>.Instance.FromRgba64(configuration, rgba64Span, destination);
+            for (int i = 0; i < source.Length; i++)
+            {
+                destination[i] = source[i].ToPixel<TPixel>();
+            }
         }
 
         /// <inheritdoc />
         [MethodImpl(InliningOptions.ShortMethod)]
         public bool Equals(Color other)
         {
-            return this.data.PackedValue == other.data.PackedValue;
+            if (this.boxedHighPrecisionPixel is null && other.boxedHighPrecisionPixel is null)
+            {
+                return this.data.PackedValue == other.data.PackedValue;
+            }
+
+            return this.boxedHighPrecisionPixel?.Equals(other.boxedHighPrecisionPixel) == true;
         }
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object obj) => obj is Color other && this.Equals(other);
-        {
-            return obj is Color other && this.Equals(other);
-        }
 
         /// <inheritdoc />
         [MethodImpl(InliningOptions.ShortMethod)]
         public override int GetHashCode()
         {
-            return this.data.PackedValue.GetHashCode();
+            if (this.boxedHighPrecisionPixel is null)
+            {
+                return this.data.PackedValue.GetHashCode();
+            }
+
+            return this.boxedHighPrecisionPixel.GetHashCode();
         }
     }
 }

src/ImageSharp/Formats/Webp/Lossless/ColorCache.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System.Runtime.CompilerServices;
+
 namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 {
     /// <summary>
@@ -41,6 +43,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// Inserts a new color into the cache.
         /// </summary>
         /// <param name="bgra">The color to insert.</param>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public void Insert(uint bgra)
         {
             int key = HashPix(bgra, this.HashShift);
@@ -52,6 +55,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// </summary>
         /// <param name="key">The key to lookup.</param>
         /// <returns>The color for the key.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public uint Lookup(int key) => this.Colors[key];
 
         /// <summary>
@@ -59,6 +63,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// </summary>
         /// <param name="bgra">The color to check.</param>
         /// <returns>The index of the color in the cache or -1 if its not present.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public int Contains(uint bgra)
         {
             int key = HashPix(bgra, this.HashShift);
@@ -70,6 +75,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// </summary>
         /// <param name="bgra">The color.</param>
         /// <returns>The index for the color.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public int GetIndex(uint bgra) => HashPix(bgra, this.HashShift);
 
         /// <summary>
@@ -77,8 +83,10 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// </summary>
         /// <param name="key">The key.</param>
         /// <param name="bgra">The color to add.</param>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public void Set(uint key, uint bgra) => this.Colors[key] = bgra;
 
+        [MethodImpl(InliningOptions.ShortMethod)]
         public static int HashPix(uint argb, int shift) => (int)((argb * HashMul) >> shift);
     }
 }

src/ImageSharp/Formats/Webp/Lossless/LosslessUtils.cs

@@ -765,6 +765,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// <summary>
         /// Fast calculation of log2(v) for integer input.
         /// </summary>
+        [MethodImpl(InliningOptions.ShortMethod)]
         public static float FastLog2(uint v) => v < LogLookupIdxMax ? WebpLookupTables.Log2Table[v] : FastLog2Slow(v);
 
         /// <summary>
@@ -793,7 +794,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 
         private static float FastSLog2Slow(uint v)
         {
-            Guard.MustBeGreaterThanOrEqualTo(v, LogLookupIdxMax, nameof(v));
+            DebugGuard.MustBeGreaterThanOrEqualTo<uint>(v, LogLookupIdxMax, nameof(v));
             if (v < ApproxLogWithCorrectionMax)
             {
                 int logCnt = 0;
@@ -1214,30 +1215,65 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
 
         private static uint ClampedAddSubtractFull(uint c0, uint c1, uint c2)
         {
-            int a = AddSubtractComponentFull(
+#if SUPPORTS_RUNTIME_INTRINSICS
-                (int)(c0 >> 24),
+            if (Sse2.IsSupported)
-                (int)(c1 >> 24),
+            {
-                (int)(c2 >> 24));
+                Vector128<byte> c0Vec = Sse2.UnpackLow(Sse2.ConvertScalarToVector128UInt32(c0).AsByte(), Vector128<byte>.Zero);
-            int r = AddSubtractComponentFull(
+                Vector128<byte> c1Vec = Sse2.UnpackLow(Sse2.ConvertScalarToVector128UInt32(c1).AsByte(), Vector128<byte>.Zero);
-                (int)((c0 >> 16) & 0xff),
+                Vector128<byte> c2Vec = Sse2.UnpackLow(Sse2.ConvertScalarToVector128UInt32(c2).AsByte(), Vector128<byte>.Zero);
-                (int)((c1 >> 16) & 0xff),
+                Vector128<short> v1 = Sse2.Add(c0Vec.AsInt16(), c1Vec.AsInt16());
-                (int)((c2 >> 16) & 0xff));
+                Vector128<short> v2 = Sse2.Subtract(v1, c2Vec.AsInt16());
-            int g = AddSubtractComponentFull(
+                Vector128<byte> b = Sse2.PackUnsignedSaturate(v2, v2);
-                (int)((c0 >> 8) & 0xff),
+                uint output = Sse2.ConvertToUInt32(b.AsUInt32());
-                (int)((c1 >> 8) & 0xff),
+                return output;
-                (int)((c2 >> 8) & 0xff));
+            }
-            int b = AddSubtractComponentFull((int)(c0 & 0xff), (int)(c1 & 0xff), (int)(c2 & 0xff));
+#endif
-            return ((uint)a << 24) | ((uint)r << 16) | ((uint)g << 8) | (uint)b;
+            {
+                int a = AddSubtractComponentFull(
+                    (int)(c0 >> 24),
+                    (int)(c1 >> 24),
+                    (int)(c2 >> 24));
+                int r = AddSubtractComponentFull(
+                    (int)((c0 >> 16) & 0xff),
+                    (int)((c1 >> 16) & 0xff),
+                    (int)((c2 >> 16) & 0xff));
+                int g = AddSubtractComponentFull(
+                    (int)((c0 >> 8) & 0xff),
+                    (int)((c1 >> 8) & 0xff),
+                    (int)((c2 >> 8) & 0xff));
+                int b = AddSubtractComponentFull((int)(c0 & 0xff), (int)(c1 & 0xff), (int)(c2 & 0xff));
+                return ((uint)a << 24) | ((uint)r << 16) | ((uint)g << 8) | (uint)b;
+            }
         }
 
         private static uint ClampedAddSubtractHalf(uint c0, uint c1, uint c2)
         {
-            uint ave = Average2(c0, c1);
+#if SUPPORTS_RUNTIME_INTRINSICS
-            int a = AddSubtractComponentHalf((int)(ave >> 24), (int)(c2 >> 24));
+            if (Sse2.IsSupported)
-            int r = AddSubtractComponentHalf((int)((ave >> 16) & 0xff), (int)((c2 >> 16) & 0xff));
+            {
-            int g = AddSubtractComponentHalf((int)((ave >> 8) & 0xff), (int)((c2 >> 8) & 0xff));
+                Vector128<byte> c0Vec = Sse2.UnpackLow(Sse2.ConvertScalarToVector128UInt32(c0).AsByte(), Vector128<byte>.Zero);
-            int b = AddSubtractComponentHalf((int)(ave & 0xff), (int)(c2 & 0xff));
+                Vector128<byte> c1Vec = Sse2.UnpackLow(Sse2.ConvertScalarToVector128UInt32(c1).AsByte(), Vector128<byte>.Zero);
-            return ((uint)a << 24) | ((uint)r << 16) | ((uint)g << 8) | (uint)b;
+                Vector128<byte> b0 = Sse2.UnpackLow(Sse2.ConvertScalarToVector128UInt32(c2).AsByte(), Vector128<byte>.Zero);
+                Vector128<short> avg = Sse2.Add(c1Vec.AsInt16(), c0Vec.AsInt16());
+                Vector128<short> a0 = Sse2.ShiftRightLogical(avg, 1);
+                Vector128<short> a1 = Sse2.Subtract(a0, b0.AsInt16());
+                Vector128<short> bgta = Sse2.CompareGreaterThan(b0.AsInt16(), a0.AsInt16());
+                Vector128<short> a2 = Sse2.Subtract(a1, bgta);
+                Vector128<short> a3 = Sse2.ShiftRightArithmetic(a2, 1);
+                Vector128<short> a4 = Sse2.Add(a0, a3).AsInt16();
+                Vector128<byte> a5 = Sse2.PackUnsignedSaturate(a4, a4);
+                uint output = Sse2.ConvertToUInt32(a5.AsUInt32());
+                return output;
+            }
+#endif
+            {
+                uint ave = Average2(c0, c1);
+                int a = AddSubtractComponentHalf((int)(ave >> 24), (int)(c2 >> 24));
+                int r = AddSubtractComponentHalf((int)((ave >> 16) & 0xff), (int)((c2 >> 16) & 0xff));
+                int g = AddSubtractComponentHalf((int)((ave >> 8) & 0xff), (int)((c2 >> 8) & 0xff));
+                int b = AddSubtractComponentHalf((int)(ave & 0xff), (int)(c2 & 0xff));
+                return ((uint)a << 24) | ((uint)r << 16) | ((uint)g << 8) | (uint)b;
+            }
         }
 
         [MethodImpl(InliningOptions.ShortMethod)]
@@ -1275,11 +1311,9 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                     Vector128<byte> pb = Sse2.UnpackLow(bc, Vector128<byte>.Zero); // |b - c|
                     Vector128<ushort> diff = Sse2.Subtract(pb.AsUInt16(), pa.AsUInt16());
                     Sse2.Store((ushort*)p, diff);
+                    int paMinusPb = output[3] + output[2] + output[1] + output[0];
+                    return (paMinusPb <= 0) ? a : b;
                 }
-
-                int paMinusPb = output[0] + output[1] + output[2] + output[3];
-
-                return (paMinusPb <= 0) ? a : b;
             }
             else
 #endif

src/ImageSharp/Image.Decode.cs

@@ -58,31 +58,42 @@ namespace SixLabors.ImageSharp
                 return null;
             }
 
-            using (IMemoryOwner<byte> buffer = config.MemoryAllocator.Allocate<byte>(headerSize, AllocationOptions.Clean))
+            // Header sizes are so small, that headersBuffer will be always stackalloc-ed in practice,
+            // and heap allocation will never happen, there is no need for the usual try-finally ArrayPool dance.
+            // The array case is only a safety mechanism following stackalloc best practices.
+            Span<byte> headersBuffer = headerSize > 512 ? new byte[headerSize] : stackalloc byte[headerSize];
+            long startPosition = stream.Position;
+
+            // Read doesn't always guarantee the full returned length so read a byte
+            // at a time until we get either our count or hit the end of the stream.
+            int n = 0;
+            int i;
+            do
             {
-                Span<byte> bufferSpan = buffer.GetSpan();
+                i = stream.Read(headersBuffer, n, headerSize - n);
-                long startPosition = stream.Position;
+                n += i;
+            }
+            while (n < headerSize && i > 0);
 
-                // Read doesn't always guarantee the full returned length so read a byte
+            stream.Position = startPosition;
-                // at a time until we get either our count or hit the end of the stream.
+
-                int n = 0;
+            // Does the given stream contain enough data to fit in the header for the format
-                int i;
+            // and does that data match the format specification?
-                do
+            // Individual formats should still check since they are public.
+            IImageFormat format = null;
+            foreach (IImageFormatDetector formatDetector in config.ImageFormatsManager.FormatDetectors)
+            {
+                if (formatDetector.HeaderSize <= headerSize)
                 {
-                    i = stream.Read(bufferSpan, n, headerSize - n);
+                    IImageFormat attemptFormat = formatDetector.DetectFormat(headersBuffer);
-                    n += i;
+                    if (attemptFormat != null)
+                    {
+                        format = attemptFormat;
+                    }
                 }
-                while (n < headerSize && i > 0);
-
-                stream.Position = startPosition;
-
-                // Does the given stream contain enough data to fit in the header for the format
-                // and does that data match the format specification?
-                // Individual formats should still check since they are public.
-                return config.ImageFormatsManager.FormatDetectors
-                    .Where(x => x.HeaderSize <= headerSize)
-                    .Select(x => x.DetectFormat(buffer.GetSpan())).LastOrDefault(x => x != null);
             }
+
+            return format;
         }
 
         /// <summary>

tests/ImageSharp.Tests/Color/ColorTests.CastTo.cs

@@ -66,7 +66,7 @@ namespace SixLabors.ImageSharp.Tests
             [Fact]
             public void Rgb24()
             {
-                var source = new Rgb24(1, 22,  231);
+                var source = new Rgb24(1, 22, 231);
 
                 // Act:
                 var color = new Color(source);
@@ -79,7 +79,7 @@ namespace SixLabors.ImageSharp.Tests
             [Fact]
             public void Bgr24()
             {
-                var source = new Bgr24(1, 22,  231);
+                var source = new Bgr24(1, 22, 231);
 
                 // Act:
                 var color = new Color(source);
@@ -88,6 +88,28 @@ namespace SixLabors.ImageSharp.Tests
                 Bgr24 data = color;
                 Assert.Equal(source, data);
             }
+
+            [Fact]
+            public void GenericPixel()
+            {
+                AssertGenericPixel(new RgbaVector(float.Epsilon, 2 * float.Epsilon, float.MaxValue, float.MinValue));
+                AssertGenericPixel(new Rgba64(1, 2, ushort.MaxValue, ushort.MaxValue - 1));
+                AssertGenericPixel(new Rgb48(1, 2, ushort.MaxValue - 1));
+                AssertGenericPixel(new La32(1, ushort.MaxValue - 1));
+                AssertGenericPixel(new L16(ushort.MaxValue - 1));
+                AssertGenericPixel(new Rgba32(1, 2, 255, 254));
+            }
+
+            private static void AssertGenericPixel<TPixel>(TPixel source)
+                where TPixel : unmanaged, IPixel<TPixel>
+            {
+                // Act:
+                var color = Color.FromPixel(source);
+
+                // Assert:
+                TPixel actual = color.ToPixel<TPixel>();
+                Assert.Equal(source, actual);
+            }
         }
     }
 }

tests/ImageSharp.Tests/Formats/WebP/LosslessUtilsTests.cs

@@ -153,9 +153,55 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
             }
         }
 
+        private static void RunPredictor12Test()
+        {
+            // arrange
+            uint[] topData = { 4294844413, 4294779388 };
+            uint left = 4294844413;
+            uint expectedResult = 4294779388;
+
+            // act
+            unsafe
+            {
+                fixed (uint* top = &topData[1])
+                {
+                    uint actual = LosslessUtils.Predictor12(left, top);
+
+                    // assert
+                    Assert.Equal(expectedResult, actual);
+                }
+            }
+        }
+
+        private static void RunPredictor13Test()
+        {
+            // arrange
+            uint[] topData = { 4278193922, 4278193666 };
+            uint left = 4278193410;
+            uint expectedResult = 4278193154;
+
+            // act
+            unsafe
+            {
+                fixed (uint* top = &topData[1])
+                {
+                    uint actual = LosslessUtils.Predictor13(left, top);
+
+                    // assert
+                    Assert.Equal(expectedResult, actual);
+                }
+            }
+        }
+
         [Fact]
         public void Predictor11_Works() => RunPredictor11Test();
 
+        [Fact]
+        public void Predictor12_Works() => RunPredictor12Test();
+
+        [Fact]
+        public void Predictor13_Works() => RunPredictor13Test();
+
         [Fact]
         public void SubtractGreen_Works() => RunSubtractGreenTest();
 
@@ -175,6 +221,18 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
         [Fact]
         public void Predictor11_WithoutSSE2_Works() => FeatureTestRunner.RunWithHwIntrinsicsFeature(RunPredictor11Test, HwIntrinsics.DisableSSE2);
 
+        [Fact]
+        public void Predictor12_WithHardwareIntrinsics_Works() => FeatureTestRunner.RunWithHwIntrinsicsFeature(RunPredictor12Test, HwIntrinsics.AllowAll);
+
+        [Fact]
+        public void Predictor12_WithoutSSE2_Works() => FeatureTestRunner.RunWithHwIntrinsicsFeature(RunPredictor12Test, HwIntrinsics.DisableSSE2);
+
+        [Fact]
+        public void Predictor13_WithHardwareIntrinsics_Works() => FeatureTestRunner.RunWithHwIntrinsicsFeature(RunPredictor13Test, HwIntrinsics.AllowAll);
+
+        [Fact]
+        public void Predictor13_WithoutSSE2_Works() => FeatureTestRunner.RunWithHwIntrinsicsFeature(RunPredictor13Test, HwIntrinsics.DisableSSE2);
+
         [Fact]
         public void SubtractGreen_WithHardwareIntrinsics_Works() => FeatureTestRunner.RunWithHwIntrinsicsFeature(RunSubtractGreenTest, HwIntrinsics.AllowAll);