Add early support for Stencil masking, rename SoftMaskImage property into MaskImage and make sure IsInlineImage is true for InlineImage

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

@@ -3,7 +3,7 @@
     using SkiaSharp;
     using System.Linq;
 
-    public class SoftMaskTests
+    public class MaskTests
     {
         [Fact]
         public void PigProductionHandbook()
@@ -17,7 +17,7 @@
                 var images = page.GetImages().ToArray();
 
                 var image1 = images[1];
-                Assert.NotNull(image1.SoftMaskImage);
+                Assert.NotNull(image1.MaskImage);
                 Assert.True(image1.TryGetPng(out var png1));
                 using (var skImage1 = SKImage.FromEncodedData(png1))
                 using (var skBitmap1 = SKBitmap.FromImage(skImage1))
@@ -27,7 +27,7 @@
                 }
 
                 var image2 = images[2];
-                Assert.NotNull(image2.SoftMaskImage);
+                Assert.NotNull(image2.MaskImage);
                 Assert.True(image2.TryGetPng(out var png2));
                 using (var skImage2 = SKImage.FromEncodedData(png2))
                 using (var skBitmap2 = SKBitmap.FromImage(skImage2))
@@ -37,5 +37,37 @@
                 }
             }
         }
+
+        [Fact]
+        public void MOZILLA_LINK_3264_0()
+        {
+            var path = IntegrationHelpers.GetDocumentPath("MOZILLA-LINK-3264-0.pdf");
+
+            using (var document = PdfDocument.Open(path, new ParsingOptions() { UseLenientParsing = true, SkipMissingFonts = true }))
+            {
+                var page = document.GetPage(1);
+
+                var images = page.GetImages().ToArray();
+
+                var image1 = images[1];
+                Assert.NotNull(image1.MaskImage);
+                Assert.True(image1.TryGetPng(out var png1));
+                using (var skImage1 = SKImage.FromEncodedData(png1))
+                using (var skBitmap1 = SKBitmap.FromImage(skImage1))
+                {
+                    var pixel = skBitmap1.GetPixel(0, 0);
+                    Assert.Equal(0, pixel.Alpha);
+                }
+
+                page = document.GetPage(2);
+
+                images = page.GetImages().ToArray();
+
+                var image2 = images[1];
+                Assert.NotNull(image2.MaskImage);
+                Assert.True(image2.TryGetPng(out var png2));
+                // TODO - Check alpha value
+            }
+        }
     }
 }

src/UglyToad.PdfPig.Tests/PublicApiScannerTests.cs

@@ -80,6 +80,7 @@
                 "UglyToad.PdfPig.Content.InlineImage",
                 "UglyToad.PdfPig.Content.IPageFactory`1",
                 "UglyToad.PdfPig.Content.IPdfImage",
+                "UglyToad.PdfPig.Content.PdfImageExtensions",
                 "UglyToad.PdfPig.Content.IResourceStore",
                 "UglyToad.PdfPig.Content.Letter",
                 "UglyToad.PdfPig.Content.MarkedContentElement",

src/UglyToad.PdfPig.Tests/TestPdfImage.cs

@@ -37,7 +37,7 @@
 
         public ReadOnlyMemory<byte> DecodedBytes { get; set; }
 
-        public IPdfImage? SoftMaskImage { get; }
+        public IPdfImage? MaskImage { get; }
 
         public bool TryGetBytesAsMemory(out ReadOnlyMemory<byte> bytes)
         {

src/UglyToad.PdfPig/Content/IPdfImage.cs

@@ -95,9 +95,10 @@
         ColorSpaceDetails? ColorSpaceDetails { get; }
 
         /// <summary>
-        /// Soft-mask image.
+        /// The image mask.
+        /// <para>Either a Soft-mask or a Stencil mask.</para>
         /// </summary>
-        IPdfImage? SoftMaskImage { get; }
+        IPdfImage? MaskImage { get; }
 
         /// <summary>
         /// Get the decoded memory of the image if applicable. For JPEG images and some other types the

src/UglyToad.PdfPig/Content/InlineImage.cs

@@ -58,7 +58,7 @@
         public ColorSpaceDetails ColorSpaceDetails { get; }
 
         /// <inheritdoc />
-        public IPdfImage? SoftMaskImage { get; }
+        public IPdfImage? MaskImage { get; }
 
         /// <summary>
         /// Create a new <see cref="InlineImage"/>.
@@ -78,6 +78,7 @@
             ColorSpaceDetails colorSpaceDetails,
             IPdfImage? softMaskImage)
         {
+            IsInlineImage = true;
             Bounds = bounds;
             WidthInSamples = widthInSamples;
             HeightInSamples = heightInSamples;
@@ -114,7 +115,7 @@
                 return b;
             }) : null;
 
-            SoftMaskImage = softMaskImage;
+            MaskImage = softMaskImage;
         }
 
         /// <inheritdoc />

src/UglyToad.PdfPig/Content/PdfImageExtensions.cs

@@ -0,0 +1,22 @@
+namespace UglyToad.PdfPig.Content
+{
+    /// <summary>
+    /// Pdf image extensions.
+    /// </summary>
+    public static class PdfImageExtensions
+    {
+        /// <summary>
+        /// <c>true</c> if the image colors needs to be reversed based on the Decode array and color space. <c>false</c> otherwise.
+        /// </summary>
+        public static bool NeedsReverseDecode(this IPdfImage pdfImage)
+        {
+            if (pdfImage.ColorSpaceDetails?.IsStencil == true)
+            {
+                // Stencil color space already takes care of reversing.
+                return false;
+            }
+
+            return pdfImage.Decode.Count >= 2 && pdfImage.Decode[0] == 1 && pdfImage.Decode[1] == 0;
+        }
+    }
+}

src/UglyToad.PdfPig/Graphics/Colors/ColorSpaceDetails.cs

@@ -15,6 +15,12 @@
     /// </summary>
     public abstract class ColorSpaceDetails
     {
+        /// <summary>
+        /// Is the color space a stencil indexed color space.
+        /// <para>Stencil color spaces take care of inverting colors based on the Decode array.</para>
+        /// </summary>
+        public bool IsStencil { get; }
+
         /// <summary>
         /// The type of the ColorSpace.
         /// </summary>
@@ -39,10 +45,11 @@
         /// <summary>
         /// Create a new <see cref="ColorSpaceDetails"/>.
         /// </summary>
-        protected internal ColorSpaceDetails(ColorSpace type)
+        protected internal ColorSpaceDetails(ColorSpace type, bool isStencil = false)
         {
             Type = type;
             BaseType = type;
+            IsStencil = isStencil;
         }
 
         /// <summary>
@@ -279,7 +286,7 @@
         internal static ColorSpaceDetails Stencil(ColorSpaceDetails colorSpaceDetails, double[] decode)
         {
             var blackIsOne = decode.Length >= 2 && decode[0] == 1 && decode[1] == 0;
-            return new IndexedColorSpaceDetails(colorSpaceDetails, 1, blackIsOne ? [255, 0] : [0, 255]);
+            return new IndexedColorSpaceDetails(colorSpaceDetails, 1, blackIsOne ? [255, 0] : [0, 255], true);
         }
 
         /// <inheritdoc/>
@@ -310,11 +317,15 @@
         /// </summary>
         public ReadOnlySpan<byte> ColorTable => colorTable;
 
+        public IndexedColorSpaceDetails(ColorSpaceDetails baseColorSpaceDetails, byte hiVal, byte[] colorTable)
+            : this(baseColorSpaceDetails, hiVal, colorTable, false)
+        { }
+
         /// <summary>
         /// Create a new <see cref="IndexedColorSpaceDetails"/>.
         /// </summary>
-        public IndexedColorSpaceDetails(ColorSpaceDetails baseColorSpaceDetails, byte hiVal, byte[] colorTable)
+        private IndexedColorSpaceDetails(ColorSpaceDetails baseColorSpaceDetails, byte hiVal, byte[] colorTable, bool isStencil)
-            : base(ColorSpace.Indexed)
+            : base(ColorSpace.Indexed, isStencil)
         {
             BaseColorSpace = baseColorSpaceDetails ?? throw new ArgumentNullException(nameof(baseColorSpaceDetails));
             HiVal = hiVal;

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

@@ -11,6 +11,19 @@
         {
             bytes = ReadOnlySpan<byte>.Empty;
 
+            if (image.MaskImage is null)
+            {
+                return false;
+            }
+
+            // Because we cannot resize images directly in PdfPig, we only
+            // apply the mask if it has the same size as the image
+            if (image.HeightInSamples != image.MaskImage.HeightInSamples ||
+                image.WidthInSamples != image.MaskImage.WidthInSamples)
+            {
+                return false;
+            }
+
             if (!image.TryGetBytesAsMemory(out var imageMemory))
             {
                 return false;
@@ -74,9 +87,24 @@
                 var numberOfComponents = image.ColorSpaceDetails!.BaseNumberOfColorComponents;
 
                 ReadOnlySpan<byte> softMask = null;
-                bool isSoftMask = image.SoftMaskImage is not null && TryGenerateSoftMask(image.SoftMaskImage, out softMask);
 
-                var builder = PngBuilder.Create(image.WidthInSamples, image.HeightInSamples, isSoftMask);
+                bool hasMask = TryGenerateSoftMask(image, out softMask);
+                Func<int, byte> getAlphaChannel = _ => byte.MaxValue;
+
+                if (hasMask)
+                {
+                    byte[] softMaskBytes = softMask.ToArray();
+                    if (image.MaskImage!.NeedsReverseDecode())
+                    {
+                        getAlphaChannel = i => Convert.ToByte(255 - softMaskBytes[i]);
+                    }
+                    else
+                    {
+                        getAlphaChannel = i => softMaskBytes[i];
+                    }
+                }
+
+                var builder = PngBuilder.Create(image.WidthInSamples, image.HeightInSamples, hasMask);
 
                 if (!IsCorrectlySized(image, bytesPure))
                 {
@@ -98,7 +126,7 @@
                              * B = 255 × (1-Y) × (1-K)
                              */
 
-                            byte a = isSoftMask ? softMask[sm++] : byte.MaxValue;
+                            byte a = getAlphaChannel(sm++);
                             double c = (bytesPure[i++] / 255d);
                             double m = (bytesPure[i++] / 255d);
                             double y = (bytesPure[i++] / 255d);
@@ -119,7 +147,7 @@
                     {
                         for (int row = 0; row < image.WidthInSamples; row++)
                         {
-                            byte a = isSoftMask ? softMask[sm++] : byte.MaxValue;
+                            byte a = getAlphaChannel(sm++);
                             builder.SetPixel(new Pixel(bytesPure[i++], bytesPure[i++], bytesPure[i++], a, false), row, col);
                         }
                     }
@@ -131,7 +159,7 @@
                     {
                         for (int row = 0; row < image.WidthInSamples; row++)
                         {
-                            byte a = isSoftMask ? softMask[i] : byte.MaxValue;
+                            byte a = getAlphaChannel(i);
                             byte pixel = bytesPure[i++];
                             builder.SetPixel(new Pixel(pixel, pixel, pixel, a, false), row, col);
                         }

src/UglyToad.PdfPig/XObjects/XObjectFactory.cs

@@ -63,13 +63,31 @@
                     throw new Exception("The SMask dictionary contains a 'Mask' or 'Smask' entry.");
                 }
 
-                var renderingIntent = xObject.DefaultRenderingIntent; // Ignored
+                XObjectContentRecord softMaskImageRecord = new XObjectContentRecord(XObjectType.Image,
-
+                    sMaskToken,
-                XObjectContentRecord softMaskImageRecord = new XObjectContentRecord(XObjectType.Image, sMaskToken, TransformationMatrix.Identity,
+                    TransformationMatrix.Identity,
-                    renderingIntent, DeviceGrayColorSpaceDetails.Instance);
+                    xObject.DefaultRenderingIntent, // Ignored
+                    DeviceGrayColorSpaceDetails.Instance);
 
                 softMaskImage = ReadImage(softMaskImageRecord, pdfScanner, filterProvider, resourceStore);
             }
+            else if (dictionary.TryGet(NameToken.Mask, out StreamToken maskStream))
+            {
+                if (maskStream.StreamDictionary.ContainsKey(NameToken.ColorSpace))
+                {
+                    throw new Exception("The SMask dictionary contains a 'ColorSpace'.");
+                }
+
+                // Stencil masking
+                XObjectContentRecord maskImageRecord = new XObjectContentRecord(XObjectType.Image,
+                    maskStream,
+                    TransformationMatrix.Identity,
+                    xObject.DefaultRenderingIntent,
+                    null);
+
+                softMaskImage = ReadImage(maskImageRecord, pdfScanner, filterProvider, resourceStore);
+                System.Diagnostics.Debug.Assert(softMaskImage.ColorSpaceDetails?.IsStencil == true);
+            }
 
             var isJpxDecode = dictionary.TryGet(NameToken.Filter, out NameToken filterName) && filterName.Equals(NameToken.JpxDecode);
 
@@ -125,9 +143,7 @@
                 }
             }
 
-            var streamToken = new StreamToken(dictionary, xObject.Stream.Data);
+            var decodedBytes = supportsFilters ? new Lazy<ReadOnlyMemory<byte>>(() => xObject.Stream.Decode(filterProvider, pdfScanner))
-
-            var decodedBytes = supportsFilters ? new Lazy<ReadOnlyMemory<byte>>(() => streamToken.Decode(filterProvider, pdfScanner))
                 : null;
 
             var decode = Array.Empty<double>();

src/UglyToad.PdfPig/XObjects/XObjectImage.cs

@@ -65,7 +65,7 @@
         public ColorSpaceDetails? ColorSpaceDetails { get; }
 
         /// <inheritdoc />
-        public IPdfImage? SoftMaskImage { get; }
+        public IPdfImage? MaskImage { get; }
 
         /// <summary>
         /// Creates a new <see cref="XObjectImage"/>.
@@ -98,7 +98,7 @@
             RawMemory = rawMemory;
             ColorSpaceDetails = colorSpaceDetails;
             memoryFactory = bytes;
-            SoftMaskImage = softMaskImage;
+            MaskImage = softMaskImage;
         }
 
         /// <inheritdoc />