From 7ece3dd84a68b75281d748ed60bce5efa4a144c5 Mon Sep 17 00:00:00 2001
From: Dmitry Pentin <riotbr3aker@gmail.com>
Date: Tue, 10 May 2022 17:11:53 +0300
Subject: [PATCH] Quality property fix

---
 .../Formats/Jpeg/JpegEncoderCore.cs           | 20 +---------
 src/ImageSharp/Formats/Jpeg/JpegMetadata.cs   | 39 ++++++++-----------
 2 files changed, 18 insertions(+), 41 deletions(-)

diff --git a/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs b/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs
index cbcaae2fc3..4c44e04961 100644
--- a/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs
+++ b/src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs
@@ -122,7 +122,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             this.WriteDefineHuffmanTables(this.scanConfig.HuffmanTables);
 
             // Write the quantization tables.
-            this.InitQuantizationTables(this.scanConfig.QuantizationTables, jpegMetadata);
+            this.WriteDefineQuantizationTables(this.scanConfig.QuantizationTables, jpegMetadata);
 
             // Write the scan header.
             this.WriteStartOfScan(this.frameConfig.Components.Length, this.frameConfig.Components);
@@ -188,22 +188,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             || colorType == JpegEncodingColor.Luminance
             || colorType == JpegEncodingColor.Rgb;
 
-        /// <summary>
-        /// Writes data to "Define Quantization Tables" block for QuantIndex.
-        /// </summary>
-        /// <param name="dqt">The "Define Quantization Tables" block.</param>
-        /// <param name="offset">Offset in "Define Quantization Tables" block.</param>
-        /// <param name="i">The quantization index.</param>
-        /// <param name="quant">The quantization table to copy data from.</param>
-        private static void WriteDataToDqt(byte[] dqt, ref int offset, QuantIndex i, ref Block8x8F quant)
-        {
-            dqt[offset++] = (byte)i;
-            for (int j = 0; j < Block8x8F.Size; j++)
-            {
-                dqt[offset++] = (byte)quant[ZigZag.ZigZagOrder[j]];
-            }
-        }
-
         /// <summary>
         /// Write the start of image marker.
         /// </summary>
@@ -707,7 +691,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </remarks>
         /// <param name="configs">Quantization tables configs.</param>
         /// <param name="metadata">Jpeg metadata instance.</param>
-        private void InitQuantizationTables(JpegQuantizationTableConfig[] configs, JpegMetadata metadata)
+        private void WriteDefineQuantizationTables(JpegQuantizationTableConfig[] configs, JpegMetadata metadata)
         {
             int dataLen = configs.Length * (1 + Block8x8.Size);
 
diff --git a/src/ImageSharp/Formats/Jpeg/JpegMetadata.cs b/src/ImageSharp/Formats/Jpeg/JpegMetadata.cs
index bb4cbeeee9..6c34036793 100644
--- a/src/ImageSharp/Formats/Jpeg/JpegMetadata.cs
+++ b/src/ImageSharp/Formats/Jpeg/JpegMetadata.cs
@@ -67,41 +67,34 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         }
 
         /// <summary>
-        /// Gets or sets the encoded quality.
+        /// Gets the encoded quality.
         /// </summary>
         /// <remarks>
         /// Note that jpeg image can have different quality for luminance and chrominance components.
-        /// This property returns maximum value of luma/chroma qualities.
+        /// This property returns maximum value of luma/chroma qualities if both are present.
         /// </remarks>
         public int Quality
         {
             get
             {
-                // Jpeg always has a luminance table thus it must have a luminance quality derived from it
-                if (!this.luminanceQuality.HasValue)
+                if (this.luminanceQuality.HasValue)
                 {
-                    return Quantization.DefaultQualityFactor;
-                }
-
-                int lumaQuality = this.luminanceQuality.Value;
+                    if (this.chrominanceQuality.HasValue)
+                    {
+                        return Math.Max(this.luminanceQuality.Value, this.chrominanceQuality.Value);
+                    }
 
-                // Jpeg might not have a chrominance table - return luminance quality (grayscale images)
-                if (!this.chrominanceQuality.HasValue)
-                {
-                    return lumaQuality;
+                    return this.luminanceQuality.Value;
                 }
+                else
+                {
+                    if (this.chrominanceQuality.HasValue)
+                    {
+                        return this.chrominanceQuality.Value;
+                    }
 
-                int chromaQuality = this.chrominanceQuality.Value;
-
-                // Theoretically, luma quality would always be greater or equal to chroma quality
-                // But we've already encountered images which can have higher quality of chroma components
-                return Math.Max(lumaQuality, chromaQuality);
-            }
-
-            set
-            {
-                this.LuminanceQuality = value;
-                this.ChrominanceQuality = value;
+                    return Quantization.DefaultQualityFactor;
+                }
             }
         }