From f8990a79b8bf93a974c2bfe33c2ad8b0119ef178 Mon Sep 17 00:00:00 2001
From: Kasper Frank <kasperdaff@gmail.com>
Date: Fri, 7 May 2021 11:51:41 +0200
Subject: [PATCH] Add indexed color space for stencils

---
 .../Images/PngFromPdfImageFactoryTests.cs     |  2 +-
 .../Graphics/Colors/ColorSpaceDetails.cs      | 20 +++++++++++++++----
 .../Util/ColorSpaceDetailsParser.cs           |  7 +++++--
 3 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/UglyToad.PdfPig.Tests/Images/PngFromPdfImageFactoryTests.cs b/src/UglyToad.PdfPig.Tests/Images/PngFromPdfImageFactoryTests.cs
index fc16c9b9..76f5dccd 100644
--- a/src/UglyToad.PdfPig.Tests/Images/PngFromPdfImageFactoryTests.cs
+++ b/src/UglyToad.PdfPig.Tests/Images/PngFromPdfImageFactoryTests.cs
@@ -150,7 +150,7 @@
             var decodedBytes = ImageHelpers.LoadFileBytes("ccittfax-decoded.bin");
             var image = new TestPdfImage
             {
-                ColorSpaceDetails = IndexedColorSpaceDetails.CCITTFaxColorSpaceDetails,
+                ColorSpaceDetails = IndexedColorSpaceDetails.StencilBlackIs1,
                 DecodedBytes = decodedBytes,
                 WidthInSamples = 1800,
                 HeightInSamples = 3113,
diff --git a/src/UglyToad.PdfPig/Graphics/Colors/ColorSpaceDetails.cs b/src/UglyToad.PdfPig/Graphics/Colors/ColorSpaceDetails.cs
index 7b613114..8a81cdee 100644
--- a/src/UglyToad.PdfPig/Graphics/Colors/ColorSpaceDetails.cs
+++ b/src/UglyToad.PdfPig/Graphics/Colors/ColorSpaceDetails.cs
@@ -85,13 +85,25 @@
     public class IndexedColorSpaceDetails : ColorSpaceDetails
     {
         /// <summary>
-        /// The lossless CCITT compression schemes are used for bitonal black and white images.
-        /// This is equivalent to an IndexedColorSpaceDetails with a black and white palette.
+        /// A color space useful for extracting stencil masks as black-and-white images.  
+        /// Index 0 is black and index 1 is white.
+        /// </summary>
+        internal static readonly IndexedColorSpaceDetails StencilBlackIs0
+            = new IndexedColorSpaceDetails(DeviceGrayColorSpaceDetails.Instance, 1, new byte[] { 0, 255 });
+
+        /// <summary>
+        /// A color space useful for extracting stencil masks as black-and-white images.  
         /// Index 0 is white and index 1 is black.
         /// </summary>
-        internal static readonly IndexedColorSpaceDetails CCITTFaxColorSpaceDetails
+        internal static readonly IndexedColorSpaceDetails StencilBlackIs1
             = new IndexedColorSpaceDetails(DeviceGrayColorSpaceDetails.Instance, 1, new byte[] { 255, 0 });
 
+        internal static ColorSpaceDetails Stencil(decimal[] decode)
+        {
+            return decode.Length >= 2 && decode[0] == 1 && decode[1] == 0 ?
+                StencilBlackIs1 : StencilBlackIs0 /* default */; 
+        }
+
         /// <summary>
         /// The base color space in which the values in the color table are to be interpreted.
         /// It can be any device or CIE-based color space or(in PDF 1.3) a Separation or DeviceN space,
@@ -119,7 +131,7 @@
             HiVal = hiVal;
             ColorTable = colorTable;
             BaseType = baseColorSpaceDetails.BaseType;
-        }
+        }
     }
 
     /// <summary>
diff --git a/src/UglyToad.PdfPig/Util/ColorSpaceDetailsParser.cs b/src/UglyToad.PdfPig/Util/ColorSpaceDetailsParser.cs
index 0e53c038..17e4130d 100644
--- a/src/UglyToad.PdfPig/Util/ColorSpaceDetailsParser.cs
+++ b/src/UglyToad.PdfPig/Util/ColorSpaceDetailsParser.cs
@@ -75,9 +75,12 @@
             ILookupFilterProvider filterProvider,
             bool cannotRecurse = false)
         {
-            if (filterProvider.GetFilters(imageDictionary).OfType<CcittFaxDecodeFilter>().Any())
+            if (imageDictionary.GetDictionaryObject(NameToken.ImageMask, NameToken.Im) != null)
             {
-                return IndexedColorSpaceDetails.CCITTFaxColorSpaceDetails;
+                var decodeRaw = imageDictionary.GetDictionaryObject(NameToken.Decode, NameToken.D) as ArrayToken
+                    ?? new ArrayToken(EmptyArray<IToken>.Instance);
+                var decode = decodeRaw.Data.OfType<NumericToken>().Select(x => x.Data).ToArray();
+                return IndexedColorSpaceDetails.Stencil(decode);
             }
 
             if (!colorSpace.HasValue)