From 30039aa6d35cf5aa15c5ea24cd35081834894d24 Mon Sep 17 00:00:00 2001
From: Kasper Frank <kasperdaff@gmail.com>
Date: Sun, 9 May 2021 18:45:26 +0200
Subject: [PATCH 1/2] Decode fix for CCITTFax Group 3 (1 dimensional version)

---
 .../Filters/CcittFaxCompressionType.cs        | 14 +++++++-----
 .../Filters/CcittFaxDecodeFilter.cs           |  8 +++----
 .../Filters/CcittFaxDecoderStream.cs          | 22 ++++---------------
 3 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/src/UglyToad.PdfPig/Filters/CcittFaxCompressionType.cs b/src/UglyToad.PdfPig/Filters/CcittFaxCompressionType.cs
index da388445..f0f372de 100644
--- a/src/UglyToad.PdfPig/Filters/CcittFaxCompressionType.cs
+++ b/src/UglyToad.PdfPig/Filters/CcittFaxCompressionType.cs
@@ -6,16 +6,20 @@
     internal enum CcittFaxCompressionType
     {
         /// <summary>
-        /// Modified Huffman - Group 3 (T4)
+        /// Modified Huffman (MH) - Group 3 variation (T2)
         /// </summary>
         ModifiedHuffman,
         /// <summary>
-        /// Modified Read - Group 3 (optional T4)
+        /// Modified Huffman (MH) - Group 3 (T4)
         /// </summary>
-        T4,
+        Group3_1D,
         /// <summary>
-        /// Modified Modified Read - Group 4 (T6)
+        /// Modified Read (MR) - Group 3 (T4)
         /// </summary>
-        T6
+        Group3_2D,
+        /// <summary>
+        /// Modified Modified Read (MMR) - Group 4 (T6)
+        /// </summary>
+        Group4_2D
     }
 }
diff --git a/src/UglyToad.PdfPig/Filters/CcittFaxDecodeFilter.cs b/src/UglyToad.PdfPig/Filters/CcittFaxDecodeFilter.cs
index 9fe84246..8cae7dd7 100644
--- a/src/UglyToad.PdfPig/Filters/CcittFaxDecodeFilter.cs
+++ b/src/UglyToad.PdfPig/Filters/CcittFaxDecodeFilter.cs
@@ -60,7 +60,7 @@
         {
             if (k == 0)
             {
-                var compressionType = CcittFaxCompressionType.T4; // Group 3 1D
+                var compressionType = CcittFaxCompressionType.Group3_1D; // Group 3 1D
 
                 if (input.Count < 20)
                 {
@@ -78,7 +78,7 @@
                         b = (short)((b << 1) + ((input[(i / 8)] >> (7 - (i % 8))) & 0x01));
                         if ((b & 0xFFF) == 1)
                         {
-                            return CcittFaxCompressionType.T4;
+                            return CcittFaxCompressionType.Group3_1D;
                         }
                     }
                 }
@@ -88,11 +88,11 @@
             else if (k > 0)
             {
                 // Group 3 2D
-                return CcittFaxCompressionType.T4;
+                return CcittFaxCompressionType.Group3_2D;
             }
             else
             {
-                return CcittFaxCompressionType.T6;
+                return CcittFaxCompressionType.Group4_2D;
             }
         }
 
diff --git a/src/UglyToad.PdfPig/Filters/CcittFaxDecoderStream.cs b/src/UglyToad.PdfPig/Filters/CcittFaxDecoderStream.cs
index 71aff5d8..89982af1 100644
--- a/src/UglyToad.PdfPig/Filters/CcittFaxDecoderStream.cs
+++ b/src/UglyToad.PdfPig/Filters/CcittFaxDecoderStream.cs
@@ -17,7 +17,6 @@
         private readonly int columns;
         private readonly byte[] decodedRow;
 
-        private readonly bool optionG32D;
         private readonly bool optionByteAligned;
         
         private readonly CcittFaxCompressionType type;
@@ -52,20 +51,6 @@
             changesCurrentRow = new int[columns + 2];
 
             optionByteAligned = byteAligned;
-            switch (type)
-            {
-                case CcittFaxCompressionType.ModifiedHuffman:
-                    optionG32D = false;
-                    break;
-                case CcittFaxCompressionType.T4:
-                    optionG32D = true;
-                    break;
-                case CcittFaxCompressionType.T6:
-                    optionG32D = false;
-                    break;
-                default:
-                    throw new ArgumentOutOfRangeException(nameof(type), type, "Illegal parameter");
-            }
         }
 
         private void Fetch()
@@ -252,7 +237,7 @@
             }
 
         done:
-            if (!optionG32D || ReadBit())
+            if (type == CcittFaxCompressionType.Group3_1D || ReadBit())
             {
                 Decode1D();
             }
@@ -279,10 +264,11 @@
                 case CcittFaxCompressionType.ModifiedHuffman:
                     DecodeRowType2();
                     break;
-                case CcittFaxCompressionType.T4:
+                case CcittFaxCompressionType.Group3_1D:
+                case CcittFaxCompressionType.Group3_2D:
                     DecodeRowType4();
                     break;
-                case CcittFaxCompressionType.T6:
+                case CcittFaxCompressionType.Group4_2D:
                     DecodeRowType6();
                     break;
                 default:

From 9f6dd5375d4ee60b76e7220077fbbbda15558dd5 Mon Sep 17 00:00:00 2001
From: Kasper Frank <kasperdaff@gmail.com>
Date: Mon, 10 May 2021 09:01:57 +0200
Subject: [PATCH 2/2] DecodeParms might be an indirect reference

---
 src/UglyToad.PdfPig/XObjects/XObjectFactory.cs | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/UglyToad.PdfPig/XObjects/XObjectFactory.cs b/src/UglyToad.PdfPig/XObjects/XObjectFactory.cs
index 57c487f0..2df928ed 100644
--- a/src/UglyToad.PdfPig/XObjects/XObjectFactory.cs
+++ b/src/UglyToad.PdfPig/XObjects/XObjectFactory.cs
@@ -10,7 +10,8 @@
     using Graphics.Colors;
     using Graphics.Core;
     using Tokenization.Scanner;
-    using Tokens;
+    using Tokens;
+    using UglyToad.PdfPig.Parser.Parts;
     using Util;
 
     internal static class XObjectFactory
@@ -99,7 +100,15 @@
                 }
             }
 
-            var decodedBytes = supportsFilters ? new Lazy<IReadOnlyList<byte>>(() => xObject.Stream.Decode(filterProvider, pdfScanner))
+            var decodeParams = dictionary.GetObjectOrDefault(NameToken.DecodeParms, NameToken.Dp);
+            if (decodeParams is IndirectReferenceToken refToken)
+            {
+                dictionary = dictionary.With(NameToken.DecodeParms, pdfScanner.Get(refToken.Data).Data);
+            }
+
+            var streamToken = new StreamToken(dictionary, xObject.Stream.Data);
+            
+            var decodedBytes = supportsFilters ? new Lazy<IReadOnlyList<byte>>(() => streamToken.Decode(filterProvider, pdfScanner))
                 : null;
 
             var decode = EmptyArray<decimal>.Instance;