Correct the JPEG decoder's summary

src/SharpCorePDF.Infrastructure/Pdf/JpegDecoder.cs

@@ -1,13 +1,14 @@
 namespace SharpCorePDF.Infrastructure.Pdf;
 
 /// <summary>
-/// Decodes a baseline (SOF0) or extended sequential (SOF1) JPEG to its samples.
+/// Decodes a JPEG — baseline, extended sequential or progressive — to its samples.
 /// </summary>
 /// <remarks>
 /// <para>
-/// The decoder is a baseline one: one scan, canonical Huffman coding, an 8 x 8 inverse DCT, and the three
-/// component layouts a PDF image states — Gray, RGB/YCbCr and CMYK/YCCK. Progressive (SOF2) is refused
-/// for now; ADR-005 records it as the next variant.
+/// The decoder reads the sequential form (SOF0/SOF1) and the progressive form (SOF2): a sequential scan
+/// is decoded in one pass, while a progressive file's scans accumulate quantised coefficients that the
+/// inverse DCT reconstructs once at the end. Both forms cover canonical Huffman coding, restart markers,
+/// an 8 x 8 inverse DCT and the component layouts a PDF image states — Gray, RGB/YCbCr and CMYK/YCCK.
 /// </para>
 /// <para>
 /// The samples are the values the JPEG stores, interleaved, one byte per component: <c>Gray8</c> for one
@@ -70,7 +71,7 @@
         out int height) =>
         new JpegDecoder(data).Run(maxBytes, out pixels, out format, out width, out height);
 
     private bool Run(int maxBytes, out byte[]? pixels, out string? format, out int width, out int height)
     {
         pixels = null;
         format = null;
@@ -450,7 +451,7 @@
         public int BlocksY { get; set; }
     }
 
     private bool DecodeScan(
         int scanStart,
         int maxBytes,
         out byte[]? pixels,
@@ -529,7 +530,7 @@
         return BuildOutput(maxBytes, out pixels, out format);
     }
 
     private bool ReconstructProgressive()
     {
         var mcuWidth = 8 * maxH;
         var mcuHeight = 8 * maxV;
@@ -576,7 +577,7 @@
         return true;
     }
 
     private bool DecodeProgressiveScan(int dataStart, out int nextOffset)
     {
         nextOffset = dataStart;
         var mcuWidth = 8 * maxH;
@@ -676,7 +677,7 @@
         return true;
     }
 
     private bool DecodeProgressiveBlock(ref JpegBits bits, JpegComponent component, int blockY, int blockX)
     {
         var block = component.Coefficients.AsSpan(((blockY * component.BlocksX) + blockX) * 64, 64);
 
@@ -937,7 +938,7 @@
         return true;
     }
 
     private bool DecodeBlock(ref JpegBits bits, JpegComponent component, int[] coefficients, byte[] samples)
     {
         var dcTable = dcTables[component.DcTable];
         var acTable = acTables[component.AcTable];
@@ -1032,7 +1033,7 @@
         }
     }
 
     private bool BuildOutput(int maxBytes, out byte[]? pixels, out string? format)
     {
         pixels = null;
         format = null;
@@ -1131,7 +1132,7 @@
     /// even output position takes three parts of its sample and one of the neighbour before it, an odd one
     /// three parts and one of the neighbour after it, rounded as libjpeg rounds.
     /// </summary>
     private static int Sample(
         byte[] plane,
         int stride,
         int rows,