From 3f612b736f46d2df4785b67b0946e1496a5a0291 Mon Sep 17 00:00:00 2001
From: Brian Popow <popow@gmx.de>
Date: Sat, 28 Nov 2020 16:56:24 +0100
Subject: [PATCH] Split up WriteBiColor in Deflate and no compression

---
 .../Formats/Tiff/Utils/TiffWriter.cs          | 82 ++++++++++++++-----
 1 file changed, 60 insertions(+), 22 deletions(-)

diff --git a/src/ImageSharp/Formats/Tiff/Utils/TiffWriter.cs b/src/ImageSharp/Formats/Tiff/Utils/TiffWriter.cs
index 3a0fcea75a..586eb0a55c 100644
--- a/src/ImageSharp/Formats/Tiff/Utils/TiffWriter.cs
+++ b/src/ImageSharp/Formats/Tiff/Utils/TiffWriter.cs
@@ -369,30 +369,33 @@ namespace SixLabors.ImageSharp.Formats.Tiff
         {
             int padding = image.Width % 8 == 0 ? 0 : 1;
             int bytesPerRow = (image.Width / 8) + padding;
-            using IMemoryOwner<L8> rowL8 = this.memoryAllocator.Allocate<L8>(image.Width);
+            using IMemoryOwner<L8> pixelRowAsGray = this.memoryAllocator.Allocate<L8>(image.Width);
             using IManagedByteBuffer row = this.memoryAllocator.AllocateManagedByteBuffer(bytesPerRow, AllocationOptions.Clean);
-            using var memoryStream = new MemoryStream();
-            using var deflateStream = new ZlibDeflateStream(this.memoryAllocator, memoryStream, PngCompressionLevel.Level6); // TODO: make compression level configurable
-            Span<byte> rowSpan = row.GetSpan();
-            Span<L8> rowL8Span = rowL8.GetSpan();
+            Span<byte> outputRow = row.GetSpan();
+            Span<L8> pixelRowAsGraySpan = pixelRowAsGray.GetSpan();
 
             // Convert image to black and white.
             using Image<TPixel> imageClone = image.Clone();
             imageClone.Mutate(img => img.BinaryDither(default(ErrorDither)));
 
+            if (compression == TiffEncoderCompression.Deflate)
+            {
+                return this.WriteBiColorDeflate(image, pixelRowAsGraySpan, outputRow);
+            }
+
             int bytesWritten = 0;
             for (int y = 0; y < image.Height; y++)
             {
                 int bitIndex = 0;
                 int byteIndex = 0;
                 Span<TPixel> pixelRow = imageClone.GetPixelRowSpan(y);
-                PixelOperations<TPixel>.Instance.ToL8(this.configuration, pixelRow, rowL8Span);
+                PixelOperations<TPixel>.Instance.ToL8(this.configuration, pixelRow, pixelRowAsGraySpan);
                 for (int x = 0; x < pixelRow.Length; x++)
                 {
                     int shift = 7 - bitIndex;
-                    if (rowL8Span[x].PackedValue == 255)
+                    if (pixelRowAsGraySpan[x].PackedValue == 255)
                     {
-                        rowSpan[byteIndex] |= (byte)(1 << shift);
+                        outputRow[byteIndex] |= (byte)(1 << shift);
                     }
 
                     bitIndex++;
@@ -403,27 +406,62 @@ namespace SixLabors.ImageSharp.Formats.Tiff
                     }
                 }
 
-                if (compression == TiffEncoderCompression.Deflate)
-                {
-                    deflateStream.Write(row);
-                }
-                else
-                {
-                    this.output.Write(row);
-                    bytesWritten += row.Length();
-                }
+                this.output.Write(row);
+                bytesWritten += row.Length();
 
                 row.Clear();
             }
 
-            if (compression == TiffEncoderCompression.Deflate)
+            return bytesWritten;
+        }
+
+        /// <summary>
+        /// Writes the image data as 1 bit black and white with deflate compression to the stream.
+        /// </summary>
+        /// <typeparam name="TPixel">The pixel data.</typeparam>
+        /// <param name="image">The image to write to the stream.</param>
+        /// <param name="pixelRowAsGraySpan">A span for converting a pixel row to gray.</param>
+        /// <param name="outputRow">A span which will be used to store the output pixels.</param>
+        /// <returns>The number of bytes written.</returns>
+        public int WriteBiColorDeflate<TPixel>(Image<TPixel> image, Span<L8> pixelRowAsGraySpan, Span<byte> outputRow)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using var memoryStream = new MemoryStream();
+            using var deflateStream = new ZlibDeflateStream(this.memoryAllocator, memoryStream, PngCompressionLevel.Level6); // TODO: make compression level configurable
+
+            int bytesWritten = 0;
+            for (int y = 0; y < image.Height; y++)
             {
-                deflateStream.Flush();
-                byte[] buffer = memoryStream.ToArray();
-                this.output.Write(buffer);
-                bytesWritten += buffer.Length;
+                int bitIndex = 0;
+                int byteIndex = 0;
+                Span<TPixel> pixelRow = image.GetPixelRowSpan(y);
+                PixelOperations<TPixel>.Instance.ToL8(this.configuration, pixelRow, pixelRowAsGraySpan);
+                for (int x = 0; x < pixelRow.Length; x++)
+                {
+                    int shift = 7 - bitIndex;
+                    if (pixelRowAsGraySpan[x].PackedValue == 255)
+                    {
+                        outputRow[byteIndex] |= (byte)(1 << shift);
+                    }
+
+                    bitIndex++;
+                    if (bitIndex == 8)
+                    {
+                        byteIndex++;
+                        bitIndex = 0;
+                    }
+                }
+
+                deflateStream.Write(outputRow);
+
+                outputRow.Clear();
             }
 
+            deflateStream.Flush();
+            byte[] buffer = memoryStream.ToArray();
+            this.output.Write(buffer);
+            bytesWritten += buffer.Length;
+
             return bytesWritten;
         }