From a95594607d120d211822464b91be0c4864936fbf Mon Sep 17 00:00:00 2001
From: winscripter <142818255+winscripter@users.noreply.github.com>
Date: Mon, 31 Aug 2026 21:11:16 +0400
Subject: [PATCH] Add JPEG data constants

---
 .../Processing/Jpeg/Data/JpegDataConstants.cs | 85 +++++++++++++++++++
 .../Formats/Jxl/Processing/Jpeg/README.md     |  2 +
 2 files changed, 87 insertions(+)

diff --git a/src/ImageSharp/Formats/Jxl/Processing/Jpeg/Data/JpegDataConstants.cs b/src/ImageSharp/Formats/Jxl/Processing/Jpeg/Data/JpegDataConstants.cs
index 525d3f4c0..7dd73a50c 100644
--- a/src/ImageSharp/Formats/Jxl/Processing/Jpeg/Data/JpegDataConstants.cs
+++ b/src/ImageSharp/Formats/Jxl/Processing/Jpeg/Data/JpegDataConstants.cs
@@ -17,4 +17,89 @@ internal static class JpegDataConstants
     /// Maximum number of quantizer tables.
     /// </summary>
     public const int MaximumQuantizationTables = 4;
+
+    /// <summary>
+    /// Maximum number of Huffman code tables.
+    /// </summary>
+    public const int MaxHuffmanTables = 4;
+
+    /// <summary>
+    /// Maximum number of bits for a Huffman code.
+    /// </summary>
+    public const int JpegHuffmanMaxBitLength = 16;
+
+    /// <summary>
+    /// Alphabet size for Huffman tables used in the JPEG format.
+    /// </summary>
+    public const int JpegHuffmanAlphabetSize = 256;
+
+    /// <summary>
+    /// Alphabet size for Huffman tables used in the JPEG format.
+    /// </summary>
+    /// <remarks>
+    /// This is specific to the DC coefficients of the Discrete
+    /// Cosine Transform.
+    /// </remarks>
+    public const int JpegDcAlphabetSize = 12;
+
+    /// <summary>
+    /// Maximum number of DHT "Define Huffman Tables" markers.
+    /// </summary>
+    public const int MaxDhtMarkers = 512;
+
+    /// <summary>
+    /// Largest value for width OR height.
+    /// </summary>
+    public const int MaxDimPixels = 65535;
+
+    /// <summary>
+    /// Marker that specifies APP1.
+    /// </summary>
+    public const int App1 = 0xE1;
+
+    /// <summary>
+    /// Marker that specifies APP2.
+    /// </summary>
+    public const int App2 = 0xE2;
+
+    /// <summary>
+    /// Gets the tag bytes specifying the ICC profile.
+    /// </summary>
+    public static ReadOnlySpan<byte> IccProfileTag => "ICC_PROFILE\0"u8;
+
+    /// <summary>
+    /// Gets the tag bytes specifying the EXIF profile.
+    /// </summary>
+    public static ReadOnlySpan<byte> ExifTag => "Exif\0\0"u8;
+
+    /// <summary>
+    /// Gets the tag bytes specifying the XMP profile.
+    /// </summary>
+    public static ReadOnlySpan<byte> XmpTag => "http://ns.adobe.com/xap/1.0/\0"u8;
+
+    public static ReadOnlySpan<int> JpegNaturalOrder =>
+    [
+        0,   1,  8, 16,  9,  2,  3, 10,
+        17, 24, 32, 25, 18, 11,  4,  5,
+        12, 19, 26, 33, 40, 48, 41, 34,
+        27, 20, 13,  6,  7, 14, 21, 28,
+        35, 42, 49, 56, 57, 50, 43, 36,
+        29, 22, 15, 23, 30, 37, 44, 51,
+        58, 59, 52, 45, 38, 31, 39, 46,
+        53, 60, 61, 54, 47, 55, 62, 63,
+        63, 63, 63, 63, 63, 63, 63, 63,
+        63, 63, 63, 63, 63, 63, 63, 63
+    ];
+
+    public static ReadOnlySpan<int> JpegZigZagOrder =>
+    [
+        0,   1,  5,  6, 14, 15, 27, 28,
+        2,   4,  7, 13, 16, 26, 29, 42,
+        3,   8, 12, 17, 25, 30, 41, 43,
+        9,  11, 18, 24, 31, 40, 44, 53,
+        10, 19, 23, 32, 39, 45, 52, 54,
+        20, 22, 33, 38, 46, 51, 55, 60,
+        21, 34, 37, 47, 50, 56, 59, 61,
+        35, 36, 48, 49, 57, 58, 62, 63
+    ];
 }
diff --git a/src/ImageSharp/Formats/Jxl/Processing/Jpeg/README.md b/src/ImageSharp/Formats/Jxl/Processing/Jpeg/README.md
index 4b98e0aff..bde5de389 100644
--- a/src/ImageSharp/Formats/Jxl/Processing/Jpeg/README.md
+++ b/src/ImageSharp/Formats/Jxl/Processing/Jpeg/README.md
@@ -7,3 +7,5 @@ This folder contains logic to:
 - JXL to JPEG
 
 This does not contain a JPEG codec.
+
+Logic in this folder is used for JPEG&lt;-&gt;JXL lossless compression.