Add sampler option, add comment.

src/ImageSharp/Formats/DecoderOptions.cs

@@ -2,6 +2,8 @@
 // Licensed under the Six Labors Split License.
 
 using System;
+using SixLabors.ImageSharp.Processing;
+using SixLabors.ImageSharp.Processing.Processors.Transforms;
 
 namespace SixLabors.ImageSharp.Formats
 {
@@ -29,6 +31,11 @@ namespace SixLabors.ImageSharp.Formats
         /// </summary>
         public Size? TargetSize { get; set; } = null;
 
+        /// <summary>
+        /// Gets or sets the sampler to use when resizing during decoding.
+        /// </summary>
+        public IResampler Sampler { get; set; } = KnownResamplers.Box;
+
         /// <summary>
         /// Gets or sets a value indicating whether to ignore encoded metadata when decoding.
         /// </summary>

src/ImageSharp/Formats/ImageDecoderUtilities.cs

@@ -29,7 +29,7 @@ namespace SixLabors.ImageSharp.Formats
                 ResizeOptions resizeOptions = new()
                 {
                     Size = options.TargetSize.Value,
-                    Sampler = KnownResamplers.Box,
+                    Sampler = options.Sampler,
                     Mode = ResizeMode.Max
                 };
 

src/ImageSharp/Formats/Jpeg/JpegDecoderResizeMode.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using SixLabors.ImageSharp.Processing;
+
 namespace SixLabors.ImageSharp.Formats.Jpeg
 {
     /// <summary>
@@ -15,7 +17,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         Combined,
 
         /// <summary>
-        /// IDCT-only to nearest block scale.
+        /// IDCT-only to nearest block scale. Similar in output to <see cref="KnownResamplers.Box"/>.
         /// </summary>
         IdctOnly,