Improves support for indexed colorspace images. Also adds rudimentary unit tests of PngFromPdfImageFactory.

src/UglyToad.PdfPig.Tests/Images/PngFromPdfImageFactoryTests.cs

@@ -0,0 +1,155 @@
+namespace UglyToad.PdfPig.Tests.Images
+{
+    using System;
+    using System.IO;
+    using System.Linq;
+    using UglyToad.PdfPig.Graphics.Colors;
+    using UglyToad.PdfPig.Images.Png;
+    using Xunit;
+
+    public class PngFromPdfImageFactoryTests
+    {
+        private static readonly byte[] RgbBlack = new byte[] { 0, 0, 0 };
+        private static readonly byte[] RgbWhite = new byte[] { 255, 255, 255 };
+        private static readonly byte[][] RgbPalette = new[] { RgbBlack, RgbWhite };
+
+        private static readonly byte[] CmykBlack = new byte[] { 0, 0, 0, 255 };
+        private static readonly byte[] CmykWhite = new byte[] { 0, 0, 0, 0 };
+
+        private static readonly byte GrayscaleBlack = 0;
+        private static readonly byte GrayscaleWhite = 255;
+
+        [Fact]
+        public void CanGeneratePngFromDeviceRgbImageData()
+        {
+            var pixels = new[]
+            {
+                RgbWhite, RgbBlack, RgbWhite,
+                RgbBlack, RgbWhite, RgbBlack,
+                RgbWhite, RgbBlack, RgbWhite
+            };
+
+            var image = new TestPdfImage
+            {
+                ColorSpaceDetails = DeviceRgbColorSpaceDetails.Instance,
+                DecodedBytes = pixels.SelectMany(b => b).ToArray(),
+                WidthInSamples = 3,
+                HeightInSamples = 3
+            };
+
+            Assert.True(PngFromPdfImageFactory.TryGenerate(image, out var bytes));
+            Assert.Equal(LoadImage("3x3.png"), bytes);
+        }
+
+        [Fact]
+        public void CanGeneratePngFromDeviceCMYKImageData()
+        {
+            var pixels = new[]
+            {
+                CmykWhite, CmykBlack, CmykWhite,
+                CmykBlack, CmykWhite, CmykBlack,
+                CmykWhite, CmykBlack, CmykWhite
+            };
+
+            var image = new TestPdfImage
+            {
+                ColorSpaceDetails = DeviceCmykColorSpaceDetails.Instance,
+                DecodedBytes = pixels.SelectMany(b => b).ToArray(),
+                WidthInSamples = 3,
+                HeightInSamples = 3
+            };
+
+            Assert.True(PngFromPdfImageFactory.TryGenerate(image, out var bytes));
+            Assert.Equal(LoadImage("3x3.png"), bytes);
+        }
+
+        [Fact]
+        public void CanGeneratePngFromDeviceGrayscaleImageData()
+        {
+            var pixels = new[]
+            {
+                GrayscaleWhite, GrayscaleBlack, GrayscaleWhite,
+                GrayscaleBlack, GrayscaleWhite, GrayscaleBlack,
+                GrayscaleWhite, GrayscaleBlack, GrayscaleWhite
+            };
+
+            var image = new TestPdfImage
+            {
+                ColorSpaceDetails = DeviceGrayColorSpaceDetails.Instance,
+                DecodedBytes = pixels,
+                WidthInSamples = 3,
+                HeightInSamples = 3
+            };
+
+            Assert.True(PngFromPdfImageFactory.TryGenerate(image, out var bytes));
+            Assert.Equal(LoadImage("3x3.png"), bytes);
+        }
+
+        [Fact]
+        public void CanGeneratePngFromIndexedImageData8bpc()
+        {
+            var indices = new byte[]
+            {
+                1, 0, 1,
+                0, 1, 0,
+                1, 0, 1
+            };
+
+            var image = new TestPdfImage
+            {
+                ColorSpaceDetails = new IndexedColorSpaceDetails(DeviceRgbColorSpaceDetails.Instance, 1, RgbPalette.SelectMany(b => b).ToArray()),
+                DecodedBytes = indices,
+                WidthInSamples = 3,
+                HeightInSamples = 3
+            };
+
+            Assert.True(PngFromPdfImageFactory.TryGenerate(image, out var bytes));
+            Assert.Equal(LoadImage("3x3.png"), bytes);
+        }
+
+        [Fact]
+        public void CanGeneratePngFromIndexedImageData1bpc()
+        {
+            // Indices for a 3x3 RGB image, each index is represented by a single bit
+            // 1, 0, 1, 
+            // 0, 1, 0,
+            // 1, 0, 1
+            //
+            // A scanline must be at least one byte wide, so the remaining five bits are padding:
+            // Byte 0: 10100000  (bits #7 and #5 are 1)
+            // Byte 1: 01000000  (bit #6 is 1)
+            // Byte 2: 10100000  (bits #7 and #5 are 1)
+            //         ||||||||
+            // Bit # : 76543210
+
+            var lines = new byte[3];
+            lines[0] |= (1 << 7); // Set bit #7 to 1
+            lines[0] |= (1 << 5); // Set bit #5 to 1
+
+            lines[1] |= (1 << 6); // Set bit #6 to 1
+
+            lines[2] |= (1 << 7); // Set bit #7 to 1
+            lines[2] |= (1 << 5); // Set bit #5 to 1
+
+            var colorTable = RgbPalette.SelectMany(b => b).ToArray();
+
+            var image = new TestPdfImage
+            {
+                ColorSpaceDetails = new IndexedColorSpaceDetails(DeviceRgbColorSpaceDetails.Instance, 1, colorTable),
+                DecodedBytes = lines,
+                WidthInSamples = 3,
+                HeightInSamples = 3,
+                BitsPerComponent = 1
+            };
+
+            Assert.True(PngFromPdfImageFactory.TryGenerate(image, out var bytes));
+            Assert.Equal(LoadImage("3x3.png"), bytes);
+        }
+
+        private static byte[] LoadImage(string name)
+        {
+            var folder = Path.GetFullPath(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "..", "..", "..", "Images", "Files"));
+            return File.ReadAllBytes(Path.Combine(folder, name));
+        }
+    }
+}

src/UglyToad.PdfPig.Tests/Integration/SwedishTouringCarChampionshipTests.cs

@@ -1,7 +1,7 @@
 namespace UglyToad.PdfPig.Tests.Integration
 {
     using Content;
-    using Images.Png;
+    using UglyToad.PdfPig.Images.Png;
     using Xunit;
 
     public class SwedishTouringCarChampionshipTests

src/UglyToad.PdfPig.Tests/TestPdfImage.cs

@@ -0,0 +1,46 @@
+namespace UglyToad.PdfPig.Tests
+{
+    using System.Collections.Generic;
+    using UglyToad.PdfPig.Content;
+    using UglyToad.PdfPig.Core;
+    using UglyToad.PdfPig.Graphics.Colors;
+    using UglyToad.PdfPig.Graphics.Core;
+    using UglyToad.PdfPig.Images.Png;
+
+    public class TestPdfImage : IPdfImage
+    {
+        public PdfRectangle Bounds { get; set; }
+
+        public int WidthInSamples { get; set; }
+
+        public int HeightInSamples { get; set; }
+
+        public ColorSpace? ColorSpace => IsImageMask ? null : ColorSpaceDetails.Type;
+
+        public int BitsPerComponent { get; set; } = 8;
+
+        public IReadOnlyList<byte> RawBytes { get; }
+
+        public RenderingIntent RenderingIntent { get; set; } = RenderingIntent.RelativeColorimetric;
+
+        public bool IsImageMask { get; set; }
+
+        public IReadOnlyList<decimal> Decode { get; set; }
+
+        public bool Interpolate { get; set; }
+
+        public bool IsInlineImage { get; set; }
+
+        public ColorSpaceDetails ColorSpaceDetails { get; set; }
+
+        public IReadOnlyList<byte> DecodedBytes { get; set; }
+
+        public bool TryGetBytes(out IReadOnlyList<byte> bytes)
+        {
+            bytes = DecodedBytes;
+            return bytes != null;
+        }
+
+        public bool TryGetPng(out byte[] bytes) => PngFromPdfImageFactory.TryGenerate(this, out bytes);
+    }
+}

src/UglyToad.PdfPig.Tests/UglyToad.PdfPig.Tests.csproj

@@ -133,4 +133,8 @@
     </None>
   </ItemGroup>
 
+  <ItemGroup>
+    <Folder Include="Images\" />
+    <Folder Include="Images\Files\" />
+  </ItemGroup>
 </Project>

src/UglyToad.PdfPig/Images/ColorSpaceDetailsByteConverter.cs

@@ -18,7 +18,7 @@
         /// change the data but for <see cref="ColorSpace.Indexed"/> it will convert the bytes which are indexes into the
         /// real pixel data into the real pixel data.
         /// </summary>
-        public static byte[] Convert(ColorSpaceDetails details, IReadOnlyList<byte> decoded)
+        public static byte[] Convert(ColorSpaceDetails details, IReadOnlyList<byte> decoded, int bitsPerComponent, int imageWidth, int imageHeight)
         {
             if (decoded == null)
             {
@@ -32,11 +32,52 @@
 
             switch (details)
             {
-                case IndexedColorSpaceDetails indexed:
-                    return UnwrapIndexedColorSpaceBytes(indexed, decoded);
+                case IndexedColorSpaceDetails indexed:
+                    if (bitsPerComponent != 8)
+                    {
+                        // To ease unwrapping further below the indices are unpacked to occupy a single byte each
+                        decoded = UnpackIndices(decoded, bitsPerComponent);
+
+                        // Remove padding bytes when the stride width differs from the image width
+                        var stride = (imageWidth * bitsPerComponent + 7) / 8;
+                        var strideWidth = stride * (8 / bitsPerComponent);
+                        if (strideWidth != imageWidth)
+                        {
+                            decoded = RemoveStridePadding(decoded.ToArray(), strideWidth, imageWidth, imageHeight);
+                        }
+                    }
+
+                    return UnwrapIndexedColorSpaceBytes(indexed, decoded);
             }
 
             return decoded.ToArray();
+        }
+
+        private static byte[] UnpackIndices(IReadOnlyList<byte> input, int bitsPerComponent)
+        {
+                IEnumerable<byte> Unpack(byte b)
+                {
+                    // Enumerate bits in bitsPerComponent-sized chunks from MSB to LSB, masking on the appropriate bits
+                    for (int i = 8 - bitsPerComponent; i >= 0; i -= bitsPerComponent)
+                    {
+                        yield return (byte)((b >> i) & ((int)Math.Pow(2, bitsPerComponent) - 1));
+                    }
+                }
+               
+                return input.SelectMany(b => Unpack(b)).ToArray();
+        }
+
+        private static byte[] RemoveStridePadding(byte[] input, int strideWidth, int imageWidth, int imageHeight)
+        {
+            var result = new byte[imageWidth * imageHeight];
+            for (int y = 0; y < imageHeight; y++)
+            {
+                int sourceIndex = y * strideWidth;
+                int targetIndex = y * imageWidth;
+                Array.Copy(input, sourceIndex, result, targetIndex, imageWidth);
+            }
+
+            return result;
         }
 
         private static byte[] UnwrapIndexedColorSpaceBytes(IndexedColorSpaceDetails indexed, IReadOnlyList<byte> input)

src/UglyToad.PdfPig/Images/Png/PngFromPdfImageFactory.cs

@@ -1,8 +1,8 @@
 namespace UglyToad.PdfPig.Images.Png
 {
     using Content;
-    using Graphics.Colors;
-
+    using Graphics.Colors;
+
     internal static class PngFromPdfImageFactory
     {
         public static bool TryGenerate(IPdfImage image, out byte[] bytes)
@@ -22,16 +22,17 @@
                 return false;
             }
 
-            bytesPure = ColorSpaceDetailsByteConverter.Convert(image.ColorSpaceDetails, bytesPure);
-
             try
             {
-                var numberOfComponents = actualColorSpace == ColorSpace.DeviceCMYK ? 4 : actualColorSpace == ColorSpace.DeviceRGB ? 3 : 1;
+                bytesPure = ColorSpaceDetailsByteConverter.Convert(image.ColorSpaceDetails, bytesPure,
+                    image.BitsPerComponent, image.WidthInSamples, image.HeightInSamples);
+
+                var numberOfComponents = actualColorSpace == ColorSpace.DeviceCMYK ? 4 : actualColorSpace == ColorSpace.DeviceRGB ? 3 : 1;
                 var is3Byte = numberOfComponents == 3;
-                
+
                 var builder = PngBuilder.Create(image.WidthInSamples, image.HeightInSamples, false);
 
-                var isCorrectlySized = bytesPure.Count == (image.WidthInSamples * image.HeightInSamples * (image.BitsPerComponent / 8) * numberOfComponents);
+                var isCorrectlySized = bytesPure.Count == (image.WidthInSamples * image.HeightInSamples * numberOfComponents);
 
                 if (!isCorrectlySized)
                 {
@@ -75,7 +76,6 @@
                 }
 
                 bytes = builder.Save();
-
                 return true;
             }
             catch
@@ -84,6 +84,6 @@
             }
 
             return false;
-        }
+        }
     }
 }