#718 #730: Add Gray8 and Gray16 Pixel Formats and clean up IPixel

src/ImageSharp/Common/Helpers/ImageMaths.cs

@@ -14,6 +14,73 @@ namespace SixLabors.ImageSharp
     /// </summary>
     internal static class ImageMaths
     {
+        /// <summary>
+        /// Gets the luminance from the rgb components using the formula as specified by ITU-R Recommendation BT.709.
+        /// </summary>
+        /// <param name="r">The red component.</param>
+        /// <param name="g">The green component.</param>
+        /// <param name="b">The blue component.</param>
+        /// <returns>The <see cref="byte"/>.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public static byte Get8BitBT709Luminance(byte r, byte g, byte b) => (byte)((r * .2126F) + (g * .7152F) + (b * .0722F));
+
+        /// <summary>
+        /// Gets the luminance from the rgb components using the formula as specified by ITU-R Recommendation BT.709.
+        /// </summary>
+        /// <param name="r">The red component.</param>
+        /// <param name="g">The green component.</param>
+        /// <param name="b">The blue component.</param>
+        /// <returns>The <see cref="ushort"/>.</returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public static ushort Get16BitBT709Luminance(ushort r, ushort g, ushort b) => (ushort)((r * .2126F) + (g * .7152F) + (b * .0722F));
+
+        /// <summary>
+        /// Scales a value from a 16 bit <see cref="ushort"/> to it's 8 bit <see cref="byte"/> equivalent.
+        /// </summary>
+        /// <param name="component">The 8 bit compoonent value.</param>
+        /// <returns>The <see cref="byte"/></returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public static byte DownScaleFrom16BitTo8Bit(ushort component)
+        {
+            // To scale to 8 bits From a 16-bit value V the required value (from the PNG specification) is:
+            //
+            //    (V * 255) / 65535
+            //
+            // This reduces to round(V / 257), or floor((V + 128.5)/257)
+            //
+            // Represent V as the two byte value vhi.vlo.  Make a guess that the
+            // result is the top byte of V, vhi, then the correction to this value
+            // is:
+            //
+            //    error = floor(((V-vhi.vhi) + 128.5) / 257)
+            //          = floor(((vlo-vhi) + 128.5) / 257)
+            //
+            // This can be approximated using integer arithmetic (and a signed
+            // shift):
+            //
+            //    error = (vlo-vhi+128) >> 8;
+            //
+            // The approximate differs from the exact answer only when (vlo-vhi) is
+            // 128; it then gives a correction of +1 when the exact correction is
+            // 0.  This gives 128 errors.  The exact answer (correct for all 16-bit
+            // input values) is:
+            //
+            //    error = (vlo-vhi+128)*65535 >> 24;
+            //
+            // An alternative arithmetic calculation which also gives no errors is:
+            //
+            //    (V * 255 + 32895) >> 16
+            return (byte)(((component * 255) + 32895) >> 16);
+        }
+
+        /// <summary>
+        /// Scales a value from an 8 bit <see cref="byte"/> to it's 16 bit <see cref="ushort"/> equivalent.
+        /// </summary>
+        /// <param name="component">The 8 bit compoonent value.</param>
+        /// <returns>The <see cref="ushort"/></returns>
+        [MethodImpl(InliningOptions.ShortMethod)]
+        public static ushort UpscaleFrom8BitTo16Bit(byte component) => (ushort)(component * 257);
+
         /// <summary>
         /// Determine the Greatest CommonDivisor (GCD) of two numbers.
         /// </summary>

src/ImageSharp/Formats/Bmp/BmpDecoderCore.cs

@@ -219,8 +219,6 @@ private void ReadRle8<TPixel>(Buffer2D<TPixel> pixels, byte[] colors, int width,
             where TPixel : struct, IPixel<TPixel>
         {
             TPixel color = default;
-            var rgba = new Rgba32(0, 0, 0, 255);
-
             using (Buffer2D<byte> buffer = this.memoryAllocator.Allocate2D<byte>(width, height, AllocationOptions.Clean))
             {
                 this.UncompressRle8(width, buffer.GetSpan());
@@ -233,8 +231,7 @@ private void ReadRle8<TPixel>(Buffer2D<TPixel> pixels, byte[] colors, int width,
 
                     for (int x = 0; x < width; x++)
                     {
-                        rgba.Bgr = Unsafe.As<byte, Bgr24>(ref colors[bufferRow[x] * 4]);
-                        color.PackFromRgba32(rgba);
+                        color.PackFromBgr24(Unsafe.As<byte, Bgr24>(ref colors[bufferRow[x] * 4]));
                         pixelRow[x] = color;
                     }
                 }
@@ -352,8 +349,6 @@ private void ReadRgbPalette<TPixel>(Buffer2D<TPixel> pixels, byte[] colors, int
             using (IManagedByteBuffer row = this.memoryAllocator.AllocateManagedByteBuffer(arrayWidth + padding, AllocationOptions.Clean))
             {
                 TPixel color = default;
-                var rgba = new Rgba32(0, 0, 0, 255);
-
                 Span<byte> rowSpan = row.GetSpan();
 
                 for (int y = 0; y < height; y++)
@@ -363,17 +358,14 @@ private void ReadRgbPalette<TPixel>(Buffer2D<TPixel> pixels, byte[] colors, int
                     int offset = 0;
                     Span<TPixel> pixelRow = pixels.GetRowSpan(newY);
 
-                    // TODO: Could use PixelOperations here!
                     for (int x = 0; x < arrayWidth; x++)
                     {
                         int colOffset = x * ppb;
                         for (int shift = 0, newX = colOffset; shift < ppb && newX < width; shift++, newX++)
                         {
                             int colorIndex = ((rowSpan[offset] >> (8 - bits - (shift * bits))) & mask) * 4;
 
-                            // Stored in b-> g-> r order.
-                            rgba.Bgr = Unsafe.As<byte, Bgr24>(ref colors[colorIndex]);
-                            color.PackFromRgba32(rgba);
+                            color.PackFromBgr24(Unsafe.As<byte, Bgr24>(ref colors[colorIndex]));
                             pixelRow[newX] = color;
                         }
 
@@ -397,7 +389,6 @@ private void ReadRgb16<TPixel>(Buffer2D<TPixel> pixels, int width, int height, b
             int padding = CalculatePadding(width, 2);
             int stride = (width * 2) + padding;
             TPixel color = default;
-            var rgba = new Rgba32(0, 0, 0, 255);
 
             using (IManagedByteBuffer buffer = this.memoryAllocator.AllocateManagedByteBuffer(stride))
             {
@@ -412,11 +403,12 @@ private void ReadRgb16<TPixel>(Buffer2D<TPixel> pixels, int width, int height, b
                     {
                         short temp = BitConverter.ToInt16(buffer.Array, offset);
 
-                        rgba.R = GetBytesFrom5BitValue((temp & Rgb16RMask) >> 10);
-                        rgba.G = GetBytesFrom5BitValue((temp & Rgb16GMask) >> 5);
-                        rgba.B = GetBytesFrom5BitValue(temp & Rgb16BMask);
+                        var rgb = new Rgb24(
+                        GetBytesFrom5BitValue((temp & Rgb16RMask) >> 10),
+                        GetBytesFrom5BitValue((temp & Rgb16GMask) >> 5),
+                        GetBytesFrom5BitValue(temp & Rgb16BMask));
 
-                        color.PackFromRgba32(rgba);
+                        color.PackFromRgb24(rgb);
                         pixelRow[x] = color;
                         offset += 2;
                     }
@@ -537,7 +529,7 @@ private void ReadInfoHeader()
             this.metaData = meta;
 
             short bitsPerPixel = this.infoHeader.BitsPerPixel;
-            var bmpMetaData = this.metaData.GetFormatMetaData(BmpFormat.Instance);
+            BmpMetaData bmpMetaData = this.metaData.GetFormatMetaData(BmpFormat.Instance);
 
             // We can only encode at these bit rates so far.
             if (bitsPerPixel.Equals((short)BmpBitsPerPixel.Pixel24)

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -101,9 +101,9 @@ public void Encode<TPixel>(Image<TPixel> image, Stream stream)
 
             var fileHeader = new BmpFileHeader(
                 type: 19778, // BM
-                offset: 54,
+                fileSize: 54 + infoHeader.ImageSize,
                 reserved: 0,
-                fileSize: 54 + infoHeader.ImageSize);
+                offset: 54);
 
 #if NETCOREAPP2_1
             Span<byte> buffer = stackalloc byte[40];

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -481,22 +481,36 @@ private void ReadFrameColors<TPixel>(ref Image<TPixel> image, ref ImageFrame<TPi
                 }
 
                 ref TPixel rowRef = ref MemoryMarshal.GetReference(imageFrame.GetPixelRowSpan(writeY));
-                var rgba = new Rgba32(0, 0, 0, 255);
+                bool transFlag = this.graphicsControlExtension.TransparencyFlag;
 
-                // #403 The left + width value can be larger than the image width
-                for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width && x < imageWidth; x++)
+                if (!transFlag)
                 {
-                    int index = Unsafe.Add(ref indicesRef, i);
-
-                    if (!this.graphicsControlExtension.TransparencyFlag
-                        || this.graphicsControlExtension.TransparencyIndex != index)
+                    // #403 The left + width value can be larger than the image width
+                    for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width && x < imageWidth; x++)
                     {
+                        int index = Unsafe.Add(ref indicesRef, i);
                         ref TPixel pixel = ref Unsafe.Add(ref rowRef, x);
-                        rgba.Rgb = colorTable[index];
-                        pixel.PackFromRgba32(rgba);
+                        Rgb24 rgb = colorTable[index];
+                        pixel.PackFromRgb24(rgb);
+
+                        i++;
                     }
+                }
+                else
+                {
+                    byte transIndex = this.graphicsControlExtension.TransparencyIndex;
+                    for (int x = descriptor.Left; x < descriptor.Left + descriptor.Width && x < imageWidth; x++)
+                    {
+                        int index = Unsafe.Add(ref indicesRef, i);
+                        if (transIndex != index)
+                        {
+                            ref TPixel pixel = ref Unsafe.Add(ref rowRef, x);
+                            Rgb24 rgb = colorTable[index];
+                            pixel.PackFromRgb24(rgb);
+                        }
 
-                    i++;
+                        i++;
+                    }
                 }
             }
 

src/ImageSharp/Formats/Gif/GifEncoderCore.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.IO;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -210,16 +211,20 @@ private int GetTransparentIndex<TPixel>(QuantizedFrame<TPixel> quantized)
         {
             // Transparent pixels are much more likely to be found at the end of a palette
             int index = -1;
-            Rgba32 trans = default;
+            int length = quantized.Palette.Length;
 
-            ref TPixel paletteRef = ref MemoryMarshal.GetReference(quantized.Palette.AsSpan());
-            for (int i = quantized.Palette.Length - 1; i >= 0; i--)
+            using (IMemoryOwner<Rgba32> rgbaBuffer = this.memoryAllocator.Allocate<Rgba32>(length))
             {
-                ref TPixel entry = ref Unsafe.Add(ref paletteRef, i);
-                entry.ToRgba32(ref trans);
-                if (trans.Equals(default))
+                Span<Rgba32> rgbaSpan = rgbaBuffer.GetSpan();
+                ref Rgba32 paletteRef = ref MemoryMarshal.GetReference(rgbaSpan);
+                PixelOperations<TPixel>.Instance.ToRgba32(quantized.Palette, rgbaSpan, length);
+
+                for (int i = quantized.Palette.Length - 1; i >= 0; i--)
                 {
-                    index = i;
+                    if (Unsafe.Add(ref paletteRef, i).Equals(default))
+                    {
+                        index = i;
+                    }
                 }
             }
 
@@ -406,24 +411,13 @@ private void WriteImageDescriptor<TPixel>(ImageFrame<TPixel> image, bool hasColo
         private void WriteColorTable<TPixel>(QuantizedFrame<TPixel> image, Stream stream)
             where TPixel : struct, IPixel<TPixel>
         {
-            int pixelCount = image.Palette.Length;
-
             // The maximium number of colors for the bit depth
             int colorTableLength = ImageMaths.GetColorCountForBitDepth(this.bitDepth) * 3;
-            Rgb24 rgb = default;
+            int pixelCount = image.Palette.Length;
 
             using (IManagedByteBuffer colorTable = this.memoryAllocator.AllocateManagedByteBuffer(colorTableLength))
             {
-                ref TPixel paletteRef = ref MemoryMarshal.GetReference(image.Palette.AsSpan());
-                ref Rgb24 rgb24Ref = ref Unsafe.As<byte, Rgb24>(ref MemoryMarshal.GetReference(colorTable.GetSpan()));
-                for (int i = 0; i < pixelCount; i++)
-                {
-                    ref TPixel entry = ref Unsafe.Add(ref paletteRef, i);
-                    entry.ToRgb24(ref rgb);
-                    Unsafe.Add(ref rgb24Ref, i) = rgb;
-                }
-
-                // Write the palette to the stream
+                PixelOperations<TPixel>.Instance.ToRgb24Bytes(image.Palette.AsSpan(), colorTable.GetSpan(), pixelCount);
                 stream.Write(colorTable.Array, 0, colorTableLength);
             }
         }