Change GrayScaleMethod from enum to delegate to allow users more cont…

samples/Synercoding.FileFormats.Pdf.ConsoleTester/Program.cs

@@ -294,7 +294,7 @@ private static void _writePdf(string fileName, bool enableSubsetting = true)
                 using (var pantherSixImage = SixLabors.ImageSharp.Image.Load<Rgba32>(pantherPngStream))
                 {
                     var pantherImg = writer.AddImage(pantherSixImage);
-                    var transparentPanther = writer.AddSeparationImage(pantherSixImage, new Separation(PdfName.Get("White"), PredefinedColors.Yellow), GrayScaleMethod.AlphaChannel, [0, 1]);
+                    var transparentPanther = writer.AddSeparationImage(pantherSixImage, new Separation(PdfName.Get("White"), PredefinedColors.Yellow), GrayScaleMethods.AlphaChannel, [0, 1]);
 
                     writer.AddPage(page =>
                     {

src/Synercoding.FileFormats.Pdf/Content/GrayScaleMethod.cs

@@ -1,36 +1,110 @@
+using SixLabors.ImageSharp.PixelFormats;
+
 namespace Synercoding.FileFormats.Pdf.Content;
 
 /// <summary>
 /// What method is used to generate a 1 component grayscale pixel byte array
 /// </summary>
-public enum GrayScaleMethod
+public static class GrayScaleMethods
 {
     /// <summary>
     /// Use the red channel
     /// </summary>
-    RedChannel,
+    public static byte RedChannel(ref Rgba32 pixel) => pixel.R;
+    /// <summary>
+    /// Use the red channel
+    /// </summary>
+    public static byte RedChannel(ref Rgb24 pixel) => pixel.R;
     /// <summary>
     /// Use the green channel
     /// </summary>
-    GreenChannel,
+    public static byte GreenChannel(ref Rgba32 pixel) => pixel.G;
+    /// <summary>
+    /// Use the green channel
+    /// </summary>
+    public static byte GreenChannel(ref Rgb24 pixel) => pixel.G;
+    /// <summary>
+    /// Use the blue channel
+    /// </summary>
+    public static byte BlueChannel(ref Rgba32 pixel) => pixel.B;
     /// <summary>
     /// Use the blue channel
     /// </summary>
-    BlueChannel,
+    public static byte BlueChannel(ref Rgb24 pixel) => pixel.B;
     /// <summary>
     /// Use the alpha channel
     /// </summary>
-    AlphaChannel,
+    public static byte AlphaChannel(ref Rgba32 pixel) => pixel.A;
+    /// <summary>
+    /// Use the average of the Red, Green and Blue channels.
+    /// </summary>
+    public static byte AverageOfRGBChannels(ref Rgba32 pixel) => (byte)( ( pixel.R + pixel.G + pixel.B ) / 3 );
     /// <summary>
     /// Use the average of the Red, Green and Blue channels.
     /// </summary>
-    AverageOfRGBChannels,
+    public static byte AverageOfRGBChannels(ref Rgb24 pixel) => (byte)( ( pixel.R + pixel.G + pixel.B ) / 3 );
+    /// <summary>
+    /// The constants defined by ITU-R BT.601 are 0.299 red + 0.587 green + 0.114 blue.
+    /// </summary>
+    public static byte BT601(ref Rgba32 pixel) => (byte)( ( pixel.R * 0.299 ) + ( pixel.G * 0.587 ) + ( pixel.B * 0.114 ) );
     /// <summary>
     /// The constants defined by ITU-R BT.601 are 0.299 red + 0.587 green + 0.114 blue.
     /// </summary>
-    BT601,
+    public static byte BT601(ref Rgb24 pixel) => (byte)( ( pixel.R * 0.299 ) + ( pixel.G * 0.587 ) + ( pixel.B * 0.114 ) );
     /// <summary>
     /// The constants defined by ITU-R BT.709 are 0.2126 red + 0.7152 green + 0.0722 blue.
     /// </summary>
-    BT709,
+    public static byte BT709(ref Rgba32 pixel) => (byte)( ( pixel.R * 0.2126 ) + ( pixel.G * 0.7152 ) + ( pixel.B * 0.0722 ) );
+    /// <summary>
+    /// The constants defined by ITU-R BT.709 are 0.2126 red + 0.7152 green + 0.0722 blue.
+    /// </summary>
+    public static byte BT709(ref Rgb24 pixel) => (byte)( ( pixel.R * 0.2126 ) + ( pixel.G * 0.7152 ) + ( pixel.B * 0.0722 ) );
+
+    /// <summary>
+    /// Create a threshold method from an initial method. The threshold method will return the lowValue if the initial method returns a value less than the threshold, and the highValue otherwise.
+    /// </summary>
+    /// <param name="initialMethod">The initial method to use.</param>
+    /// <param name="threshold">The threshold value.</param>
+    /// <param name="lowValue">The value to return if the initial method returns a value less than the threshold.</param>
+    /// <param name="highValue">The value to return if the initial method returns a value greater than or equal to the threshold.</param>
+    /// <returns>The threshold method.</returns>
+    public static GrayScaleMethod32 Threshold(GrayScaleMethod32 initialMethod, byte threshold, byte lowValue = 0x00, byte highValue = 0xFF)
+    {
+        return (ref Rgba32 pixel) =>
+        {
+            var value = initialMethod(ref pixel);
+            return value < threshold ? lowValue : highValue;
+        };
+    }
+
+    /// <summary>
+    /// Create a threshold method from an initial method. The threshold method will return the lowValue if the initial method returns a value less than the threshold, and the highValue otherwise.
+    /// </summary>
+    /// <param name="initialMethod">The initial method to use.</param>
+    /// <param name="threshold">The threshold value.</param>
+    /// <param name="lowValue">The value to return if the initial method returns a value less than the threshold.</param>
+    /// <param name="highValue">The value to return if the initial method returns a value greater than or equal to the threshold.</param>
+    /// <returns>The threshold method.</returns>
+    public static GrayScaleMethod24 Threshold(GrayScaleMethod24 initialMethod, byte threshold, byte lowValue = 0x00, byte highValue = 0xFF)
+    {
+        return (ref Rgb24 pixel) =>
+        {
+            var value = initialMethod(ref pixel);
+            return value < threshold ? lowValue : highValue;
+        };
+    }
 }
+
+/// <summary>
+/// Represents a method to convert a <see cref="Rgba32"/> pixel into a single byte.
+/// </summary>
+/// <param name="pixel">The pixel to convert</param>
+/// <returns>The byte value the pixel represents.</returns>
+public delegate byte GrayScaleMethod32(ref Rgba32 pixel);
+
+/// <summary>
+/// Represents a method to convert a <see cref="Rgb24"/> pixel into a single byte.
+/// </summary>
+/// <param name="pixel">The pixel to convert</param>
+/// <returns>The byte value the pixel represents.</returns>
+public delegate byte GrayScaleMethod24(ref Rgb24 pixel);

src/Synercoding.FileFormats.Pdf/Content/PdfImage.cs

@@ -151,14 +151,14 @@ internal static PdfImage Get(TableBuilder tableBuilder, Image<Rgba32> image)
     internal static PdfImage Get(TableBuilder tableBuilder, Image<Rgb24> image)
         => new PdfImage(tableBuilder.ReserveId(), _encodeToJpg(image), image.Width, image.Height, DeviceRGB.Instance, null, null, (PdfNames.DCTDecode, null));
 
-    internal static PdfImage GetSeparation(TableBuilder tableBuilder, Image<Rgb24> image, Separation separation, GrayScaleMethod grayScaleMethod, double[]? decodeArray = null)
+    internal static PdfImage GetSeparation(TableBuilder tableBuilder, Image<Rgb24> image, Separation separation, GrayScaleMethod24 grayScaleMethod, double[]? decodeArray = null)
     {
         using var grayScaleStream = AsGrayScaleByteStream(image, grayScaleMethod);
 
         return new PdfImage(tableBuilder.ReserveId(), _flateEncode(grayScaleStream), image.Width, image.Height, separation, null, decodeArray, (PdfNames.FlateDecode, null));
     }
 
-    internal static PdfImage GetSeparation(TableBuilder tableBuilder, Image<Rgba32> image, Separation separation, GrayScaleMethod grayScaleMethod, double[]? decodeArray = null)
+    internal static PdfImage GetSeparation(TableBuilder tableBuilder, Image<Rgba32> image, Separation separation, GrayScaleMethod32 grayScaleMethod, double[]? decodeArray = null)
     {
         using var grayScaleStream = AsGrayScaleByteStream(image, grayScaleMethod);
 
@@ -170,7 +170,7 @@ internal static PdfImage GetSeparation(TableBuilder tableBuilder, Image<Rgba32>
         if (!_hasTransparancy(image))
             return null;
 
-        using var grayScaleStream = AsGrayScaleByteStream(image, GrayScaleMethod.AlphaChannel);
+        using var grayScaleStream = AsGrayScaleByteStream(image, GrayScaleMethods.AlphaChannel);
 
         return new PdfImage(tableBuilder.ReserveId(), _flateEncode(grayScaleStream), image.Width, image.Height, DeviceGray.Instance, null, null, (PdfNames.FlateDecode, null));
     }
@@ -214,7 +214,7 @@ private static Stream _flateEncode(MemoryStream stream)
         return new MemoryStream(bytes);
     }
 
-    internal static MemoryStream AsGrayScaleByteStream(Image<Rgba32> image, GrayScaleMethod grayScaleMethod)
+    internal static MemoryStream AsGrayScaleByteStream(Image<Rgba32> image, GrayScaleMethod32 grayScaleMethod)
     {
         var byteStream = new MemoryStream();
 
@@ -231,17 +231,7 @@ internal static MemoryStream AsGrayScaleByteStream(Image<Rgba32> image, GrayScal
                     // Get a reference to the pixel at position x
                     ref Rgba32 pixel = ref pixelRow[x];
 
-                    var pixelValue = grayScaleMethod switch
-                    {
-                        GrayScaleMethod.AlphaChannel => pixel.A,
-                        GrayScaleMethod.RedChannel => pixel.R,
-                        GrayScaleMethod.GreenChannel => pixel.G,
-                        GrayScaleMethod.BlueChannel => pixel.B,
-                        GrayScaleMethod.AverageOfRGBChannels => (byte)( ( pixel.R + pixel.G + pixel.B ) / 3 ),
-                        GrayScaleMethod.BT601 => (byte)( ( pixel.R * 0.299 ) + ( pixel.G * 0.587 ) + ( pixel.B * 0.114 ) ),
-                        GrayScaleMethod.BT709 => (byte)( ( pixel.R * 0.2126 ) + ( pixel.G * 0.7152 ) + ( pixel.B * 0.0722 ) ),
-                        _ => throw new NotImplementedException()
-                    };
+                    var pixelValue = grayScaleMethod(ref pixel);
 
                     byteStream.WriteByte(pixelValue);
                 }
@@ -253,11 +243,8 @@ internal static MemoryStream AsGrayScaleByteStream(Image<Rgba32> image, GrayScal
         return byteStream;
     }
 
-    internal static MemoryStream AsGrayScaleByteStream(Image<Rgb24> image, GrayScaleMethod grayScaleMethod)
+    internal static MemoryStream AsGrayScaleByteStream(Image<Rgb24> image, GrayScaleMethod24 grayScaleMethod)
     {
-        if (grayScaleMethod == GrayScaleMethod.AlphaChannel)
-            throw new ArgumentException($"Can not use alpha channel for images of pixel format {nameof(Rgb24)}.", nameof(grayScaleMethod));
-
         var byteStream = new MemoryStream();
 
         image.ProcessPixelRows(accessor =>
@@ -273,16 +260,7 @@ internal static MemoryStream AsGrayScaleByteStream(Image<Rgb24> image, GrayScale
                     // Get a reference to the pixel at position x
                     ref Rgb24 pixel = ref pixelRow[x];
 
-                    var pixelValue = grayScaleMethod switch
-                    {
-                        GrayScaleMethod.RedChannel => pixel.R,
-                        GrayScaleMethod.GreenChannel => pixel.G,
-                        GrayScaleMethod.BlueChannel => pixel.B,
-                        GrayScaleMethod.AverageOfRGBChannels => (byte)( ( pixel.R + pixel.G + pixel.B ) / 3 ),
-                        GrayScaleMethod.BT601 => (byte)( ( pixel.R * 0.299 ) + ( pixel.G * 0.587 ) + ( pixel.B * 0.114 ) ),
-                        GrayScaleMethod.BT709 => (byte)( ( pixel.R * 0.2126 ) + ( pixel.G * 0.7152 ) + ( pixel.B * 0.0722 ) ),
-                        _ => throw new NotImplementedException()
-                    };
+                    var pixelValue = grayScaleMethod(ref pixel);
 
                     byteStream.WriteByte(pixelValue);
                 }

src/Synercoding.FileFormats.Pdf/Generation/PageResources.cs

@@ -69,8 +69,9 @@ public PdfName AddJpgUnsafe(Stream jpgStream, int originalWidth, int originalHei
         return Add(pdfImage);
     }
 
-    public PdfName Add(SixLabors.ImageSharp.Image<Rgba32> image, Separation separation, GrayScaleMethod grayScaleMethod = GrayScaleMethod.AverageOfRGBChannels)
+    public PdfName Add(SixLabors.ImageSharp.Image<Rgba32> image, Separation separation, GrayScaleMethod32? grayScaleMethod = null)
     {
+        grayScaleMethod ??= GrayScaleMethods.AverageOfRGBChannels;
         var pdfImage = PdfImage.GetSeparation(_tableBuilder, image, separation, grayScaleMethod);
 
         return Add(pdfImage);

src/Synercoding.FileFormats.Pdf/PdfWriter.cs

@@ -169,8 +169,9 @@ public PdfImage AddImage(SixLabors.ImageSharp.Image<Rgb24> image)
     /// <param name="grayScaleMethod">The method to convert to grayscale.</param>
     /// <param name="decodeArray">Optional decode array for the image.</param>
     /// <returns>The added PDF image.</returns>
-    public PdfImage AddSeparationImage(SixLabors.ImageSharp.Image<Rgba32> image, Separation separation, GrayScaleMethod grayScaleMethod = GrayScaleMethod.AverageOfRGBChannels, double[]? decodeArray = null)
+    public PdfImage AddSeparationImage(SixLabors.ImageSharp.Image<Rgba32> image, Separation separation, GrayScaleMethod32? grayScaleMethod = null, double[]? decodeArray = null)
     {
+        grayScaleMethod ??= GrayScaleMethods.AverageOfRGBChannels;
         var pdfImage = PdfImage.GetSeparation(_objectWriter.TableBuiler, image, separation, grayScaleMethod, decodeArray);
 
         _objectWriter.Write(pdfImage.ToStreamObject(_cachedResources));
@@ -193,8 +194,9 @@ public PdfImage AddSeparationImage(SixLabors.ImageSharp.Image<Rgba32> image, Sep
     /// <param name="grayScaleMethod">The method to convert to grayscale.</param>
     /// <param name="decodeArray">Optional decode array for the image.</param>
     /// <returns>The added PDF image.</returns>
-    public PdfImage AddSeparationImage(SixLabors.ImageSharp.Image<Rgb24> image, Separation separation, GrayScaleMethod grayScaleMethod = GrayScaleMethod.AverageOfRGBChannels, double[]? decodeArray = null)
+    public PdfImage AddSeparationImage(SixLabors.ImageSharp.Image<Rgb24> image, Separation separation, GrayScaleMethod24? grayScaleMethod = null, double[]? decodeArray = null)
     {
+        grayScaleMethod ??= GrayScaleMethods.AverageOfRGBChannels;
         var pdfImage = PdfImage.GetSeparation(_objectWriter.TableBuiler, image, separation, grayScaleMethod, decodeArray);
 
         _objectWriter.Write(pdfImage.ToStreamObject(_cachedResources));

tests/Synercoding.FileFormats.Pdf.Tests/Generation/PageResourcesTests.cs

@@ -283,7 +283,7 @@ public void Test_Add_ImageSharp_WithSeparation()
         var separation = new Separation(PdfName.Get("SpotColor"), new RgbColor(0, 1, 0)); // Green
 
         // Act
-        var name = _pageResources.Add(image, separation, GrayScaleMethod.AverageOfRGBChannels);
+        var name = _pageResources.Add(image, separation, GrayScaleMethods.AverageOfRGBChannels);
 
         // Assert
         Assert.NotNull(name);