Added support for JBIG2

Author: dmester

docs/development-resources.md

@@ -38,6 +38,14 @@ https://koushtav.me/jpeg/tutorial/2017/11/25/lets-write-a-simple-jpeg-library-pa
 https://koushtav.me/jpeg/tutorial/c++/decoder/2019/03/02/lets-write-a-simple-jpeg-library-part-2/
 
 
+## JBIG2
+
+### STDU Viewer
+The JBI2 support in image viewers are rare. This is a tool that supports opening JBIG2 files.
+
+http://www.stdutility.com/stduviewer.html
+
+
 ## Fonts
 
 ### fontbakery

docs/limitations.md

@@ -6,13 +6,13 @@ This is a incomplete summary of non-supported features.
 
 ## Image formats
 
-The by far most commonly used image formats in PDFs are images encoded with DCTDecode (JPEG) and FlateDecode (PNG alike). Those are supported, with the exception that DCTDecode is only supported for RGB images.
+The by far most commonly used image formats in PDFs are images encoded with DCTDecode (JPEG) and FlateDecode (PNG alike). Those are supported, with the exception that DCTDecode is not supported for
+progressive CMYK or YCCK images.
 
 The following image formats are not supported:
 
 * JPEG 2000
 * Progressive CMYK or YCCK JPEG
-* JBIG2
 
 ## Color spaces
 

docs/specifications.md

@@ -54,6 +54,11 @@ T.6 : Facsimile coding schemes and coding control functions for Group 4 facsimil
 
 https://www.itu.int/rec/T-REC-T.6/en
 
+### JBIG2
+ITU-T Rec. T.88 - ISO/IEC 14492 – Lossy/lossless coding of bi-level images
+
+https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=13688&lang=en
+
 
 ## Fonts
 

src/PdfToSvg/Common/ArrayUtils.cs

@@ -93,6 +93,24 @@ public static T[] Concat<T>(params T[]?[] arrays)
             return result;
         }
 
+        public static bool StartsWith(byte[] data, int offset, int count, byte[] lookFor)
+        {
+            if (lookFor.Length > count)
+            {
+                return false;
+            }
+
+            for (var i = 0; i < lookFor.Length; i++)
+            {
+                if (data[offset + i] != lookFor[i])
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
 #if (NET40 || NET45)
         private class EmptyArrayHolder<T>
         {

src/PdfToSvg/Common/BitReaderUtils.cs

@@ -28,7 +28,7 @@ public static string FormatDebugView(ArraySegment<byte> buffer, int byteCursor,
 
         public static string FormatDebugView(ArraySegment<byte> buffer, int byteCursor, int bitCursor, int currentByte)
         {
-            var result = "";
+            var result = byteCursor + ":" + bitCursor + " ";
 
             string Format(int cursorOffset)
             {

src/PdfToSvg/Common/MathUtils.cs

@@ -115,5 +115,53 @@ public static int IntLog2(int value)
 
             return result;
         }
+
+        public static int IntLog2Ceil(int value)
+        {
+            var result = 0;
+
+            value--;
+
+            while (value > 0)
+            {
+                result++;
+                value >>= 1;
+            }
+
+            return result;
+        }
+
+        public static int FloorDiv(int x, int y)
+        {
+            var neg = false;
+
+            if (x < 0)
+            {
+                neg = true;
+                x = -x;
+            }
+
+            if (y < 0)
+            {
+                neg ^= true;
+                y = -y;
+            }
+
+            if (neg)
+            {
+                x += y - 1;
+            }
+
+            var result = x / y;
+
+            if (neg)
+            {
+                return -result;
+            }
+            else
+            {
+                return result;
+            }
+        }
     }
 }

src/PdfToSvg/DocumentModel/Names.cs

@@ -192,6 +192,7 @@ internal static class Names
         public static PdfName LZWDecode { get; } = new PdfName("LZWDecode");
         public static PdfName CCITTFaxDecode { get; } = new PdfName("CCITTFaxDecode");
         public static PdfName RunLengthDecode { get; } = new PdfName("RunLengthDecode");
+        public static PdfName JBIG2Decode { get; } = new PdfName("JBIG2Decode");
 
         public static PdfName DecodeParms { get; } = new PdfName("DecodeParms");
         public static PdfName EarlyChange { get; } = new PdfName("EarlyChange");
@@ -206,6 +207,7 @@ internal static class Names
         public static PdfName BitsPerFlag { get; } = new PdfName("BitsPerFlag");
         public static PdfName Colors { get; } = new PdfName("Colors");
         public static PdfName Interpolate { get; } = new PdfName("Interpolate");
+        public static PdfName JBIG2Globals { get; } = new PdfName("JBIG2Globals");
 
         public static PdfName ColorSpace { get; } = new PdfName("ColorSpace");
         public static PdfName DeviceGray { get; } = new PdfName("DeviceGray");

src/PdfToSvg/Filters/Filter.cs

@@ -21,7 +21,7 @@ internal abstract class Filter
         public static Filter FlateDecode { get; } = new FlateDecodeFilter();
         public static Filter LzwDecode { get; } = new LzwDecodeFilter();
         public static Filter RunLengthDecode { get; } = new RunLengthDecodeFilter();
-
+        public static Filter Jbig2Decode { get; } = new DctDecodeFilter();
         public static Filter CcittFaxDecode { get; } = new CcittFaxDecodeFilter();
 
         private static readonly Dictionary<PdfName, Filter> filters = new Dictionary<PdfName, Filter>
@@ -41,6 +41,7 @@ internal abstract class Filter
             { AbbreviatedNames.LZW, LzwDecode },
             { Names.RunLengthDecode, RunLengthDecode },
             { AbbreviatedNames.RL, RunLengthDecode },
+            { Names.JBIG2Decode, Jbig2Decode },
         };
 
         public abstract Stream Decode(Stream encodedStream, PdfDictionary? decodeParms);

src/PdfToSvg/Filters/Jbig2DecodeFilter.cs

@@ -0,0 +1,20 @@
+// Copyright (c) PdfToSvg.NET contributors.
+// https://github.com/dmester/pdftosvg.net
+// Licensed under the MIT License.
+
+using PdfToSvg.DocumentModel;
+using PdfToSvg.Filters;
+using System;
+using System.IO;
+using System.IO.Compression;
+
+namespace PdfToSvg.Filters
+{
+    internal class Jbig2DecodeFilter : Filter
+    {
+        public override Stream Decode(Stream stream, PdfDictionary? decodeParms)
+        {
+            throw new NotSupportedException("Jbig2DecodeFilter is only supported for image streams.");
+        }
+    }
+}