memory improvements

src/ImageSharp/Metadata/Profiles/Exif/ExifEncodedStringHelpers.cs

@@ -69,17 +69,25 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
         public static uint GetDataLength(EncodedString encodedString) =>
             (uint)GetEncoding(encodedString.Code).GetByteCount(encodedString.Text) + CharacterCodeBytesLength;
 
-        public static byte[] GetData(EncodedString encodedString)
+        public static int Write(EncodedString encodedString, Span<byte> destination)
         {
-            int length = (int)GetDataLength(encodedString);
-            byte[] buffer = new byte[length];
-
-            GetCodeBytes(encodedString.Code).CopyTo(buffer);
+            GetCodeBytes(encodedString.Code).CopyTo(destination);
 
             string text = encodedString.Text;
-            GetEncoding(encodedString.Code).GetBytes(text, 0, text.Length, buffer, CharacterCodeBytesLength);
+            int count = Write(GetEncoding(encodedString.Code), text, destination.Slice(CharacterCodeBytesLength));
+
+            return CharacterCodeBytesLength + count;
+        }
 
-            return buffer;
+        public static unsafe int Write(Encoding encoding, string value, Span<byte> destination)
+        {
+            fixed (char* c = value)
+            {
+                fixed (byte* b = destination)
+                {
+                    return encoding.GetBytes(c, value.Length, b, destination.Length);
+                }
+            }
         }
 
         private static bool TryDetect(ReadOnlySpan<byte> buffer, out CharacterCode code)

src/ImageSharp/Metadata/Profiles/Exif/ExifUcs2StringHelpers.cs

@@ -15,5 +15,7 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
             ExifTagValue.XPAuthor or ExifTagValue.XPComment or ExifTagValue.XPKeywords or ExifTagValue.XPSubject or ExifTagValue.XPTitle => true,
             _ => false,
         };
+
+        public static int Write(string value, Span<byte> destination) => ExifEncodedStringHelpers.Write(Ucs2Encoding, value, destination);
     }
 }

src/ImageSharp/Metadata/Profiles/Exif/ExifWriter.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Buffers.Binary;
 using System.Collections.Generic;
-using System.Text;
 
 namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 {
@@ -388,18 +387,8 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
                     return offset + 1;
                 case ExifDataType.Byte:
                 case ExifDataType.Undefined:
-                    if (value is byte[] array)
-                    {
-                        // used by encoded strings (which  dataType is Byte/Undefined)
-                        offset = Write(array, destination, offset);
-                        return offset;
-                    }
-                    else
-                    {
-                        destination[offset] = (byte)value;
-                        return offset + 1;
-                    }
-
+                    destination[offset] = (byte)value;
+                    return offset + 1;
                 case ExifDataType.DoubleFloat:
                     return WriteDouble((double)value, destination, offset);
                 case ExifDataType.Short:
@@ -446,11 +435,11 @@ namespace SixLabors.ImageSharp.Metadata.Profiles.Exif
 
             if (ExifUcs2StringHelpers.IsUcs2Tag((ExifTagValue)(ushort)exifValue.Tag))
             {
-                value = ExifUcs2StringHelpers.Ucs2Encoding.GetBytes((string)value);
+                return offset + ExifUcs2StringHelpers.Write((string)value, destination.Slice(offset));
             }
             else if (value is EncodedString encodedString)
             {
-                value = ExifEncodedStringHelpers.GetData(encodedString);
+                return offset + ExifEncodedStringHelpers.Write(encodedString, destination.Slice(offset));
             }
 
             if (exifValue.IsArray)