Use static Encoding.ASCII property

src/ImageSharp/Formats/Gif/GifConstants.cs

@@ -104,7 +104,7 @@ namespace SixLabors.ImageSharp.Formats.Gif
         /// <summary>
         /// Gets the default encoding to use when reading comments.
         /// </summary>
-        public static readonly Encoding DefaultEncoding = Encoding.GetEncoding("ASCII");
+        public static readonly Encoding DefaultEncoding = Encoding.ASCII;
 
         /// <summary>
         /// The list of mimetypes that equate to a gif.

src/ImageSharp/Formats/Png/PngConstants.cs

@@ -14,7 +14,7 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <summary>
         /// The default encoding for text metadata.
         /// </summary>
-        public static readonly Encoding DefaultEncoding = Encoding.GetEncoding("ASCII");
+        public static readonly Encoding DefaultEncoding = Encoding.ASCII;
 
         /// <summary>
         /// The list of mimetypes that equate to a png.

src/ImageSharp/MetaData/Profiles/ICC/DataReader/IccDataReader.cs

@@ -11,7 +11,7 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Icc
     /// </summary>
     internal sealed partial class IccDataReader
     {
-        private static readonly Encoding AsciiEncoding = Encoding.GetEncoding("ASCII");
+        private static readonly Encoding AsciiEncoding = Encoding.ASCII;
 
         /// <summary>
         /// The data that is read

src/ImageSharp/MetaData/Profiles/ICC/DataWriter/IccDataWriter.cs

@@ -13,7 +13,7 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Icc
     internal sealed partial class IccDataWriter : IDisposable
     {
         private static readonly bool IsLittleEndian = BitConverter.IsLittleEndian;
-        private static readonly Encoding AsciiEncoding = Encoding.GetEncoding("ASCII");
+        private static readonly Encoding AsciiEncoding = Encoding.ASCII;
 
         /// <summary>
         /// The underlying stream where the data is written to

src/ImageSharp/MetaData/Profiles/ICC/TagDataEntries/IccDataTagDataEntry.cs

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.MetaData.Profiles.Icc
     /// </summary>
     internal sealed class IccDataTagDataEntry : IccTagDataEntry, IEquatable<IccDataTagDataEntry>
     {
-        private static readonly Encoding AsciiEncoding = Encoding.GetEncoding("ASCII");
+        private static readonly Encoding AsciiEncoding = Encoding.ASCII;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="IccDataTagDataEntry"/> class.

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.Chunks.cs

@@ -113,7 +113,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
         {
             // Needs a minimum length of 9 for pHYs chunk.
             memStream.Write(new byte[] { 0, 0, 0, 9 }, 0, 4);
-            memStream.Write(Encoding.GetEncoding("ASCII").GetBytes(chunkName), 0, 4); // 4 bytes chunk header
+            memStream.Write(Encoding.ASCII.GetBytes(chunkName), 0, 4); // 4 bytes chunk header
             memStream.Write(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 }, 0, 9); // 9 bytes of chunk data
             memStream.Write(new byte[] { 0, 0, 0, 0 }, 0, 4); // Junk Crc
         }