Don't use ToArray() when we don't need to.

Directory.Build.props

@@ -31,27 +31,27 @@
 
   <!--
     https://apisof.net/
-    +===================+=======+==========+=====================+=============+=================+====================+==============+
-    | SUPPORTS          | MATHF | HASHCODE | EXTENDED_INTRINSICS | SPAN_STREAM | ENCODING_STRING | RUNTIME_INTRINSICS | CODECOVERAGE |
-    +===================+=======+==========+=====================+=============+=================+====================+==============+
-    | netcoreapp3.1     |   Y   |    Y     |         Y           |      Y      |        Y        |        Y           |      Y       |
-    | netcoreapp2.1     |   Y   |    Y     |         Y           |      Y      |        Y        |        N           |      Y       |
-    | netcoreapp2.0     |   Y   |    N     |         N           |      N      |        N        |        N           |      Y       |
-    | netstandard2.1    |   Y   |    Y     |         N           |      Y      |        Y        |        N           |      Y       |
-    | netstandard2.0    |   N   |    N     |         N           |      N      |        N        |        N           |      Y       |
-    | netstandard1.3    |   N   |    N     |         N           |      N      |        N        |        N           |      N       |
-    | net472            |   N   |    N     |         Y           |      N      |        N        |        N           |      Y       |
-    +===================+=======+==========+=====================+=============+=================+====================+==============+
+    +===================+=======+==========+=====================+=============+=================+====================+==============+============+
+    | SUPPORTS          | MATHF | HASHCODE | EXTENDED_INTRINSICS | SPAN_STREAM | ENCODING_STRING | RUNTIME_INTRINSICS | CODECOVERAGE | BASE64SPAN |
+    +===================+=======+==========+=====================+=============+=================+====================+==============+============+
+    | netcoreapp3.1     |   Y   |    Y     |         Y           |      Y      |        Y        |        Y           |      Y       |      Y     |
+    | netcoreapp2.1     |   Y   |    Y     |         Y           |      Y      |        Y        |        N           |      Y       |      Y     |     
+    | netcoreapp2.0     |   Y   |    N     |         N           |      N      |        N        |        N           |      Y       |      Y     |
+    | netstandard2.1    |   Y   |    Y     |         N           |      Y      |        Y        |        N           |      Y       |      N     |
+    | netstandard2.0    |   N   |    N     |         N           |      N      |        N        |        N           |      Y       |      N     |
+    | netstandard1.3    |   N   |    N     |         N           |      N      |        N        |        N           |      N       |      N     |
+    | net472            |   N   |    N     |         Y           |      N      |        N        |        N           |      Y       |      N     |
+    +===================+=======+==========+=====================+=============+=================+====================+==============+============+
     -->
 
   <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1'">
-    <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_HASHCODE;SUPPORTS_EXTENDED_INTRINSICS;SUPPORTS_SPAN_STREAM;SUPPORTS_ENCODING_STRING;SUPPORTS_RUNTIME_INTRINSICS;SUPPORTS_CODECOVERAGE</DefineConstants>
+    <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_HASHCODE;SUPPORTS_EXTENDED_INTRINSICS;SUPPORTS_SPAN_STREAM;SUPPORTS_ENCODING_STRING;SUPPORTS_RUNTIME_INTRINSICS;SUPPORTS_CODECOVERAGE;SUPPORTS_BASE64SPAN</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp2.1'">
-    <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_HASHCODE;SUPPORTS_EXTENDED_INTRINSICS;SUPPORTS_SPAN_STREAM;SUPPORTS_ENCODING_STRING;SUPPORTS_CODECOVERAGE</DefineConstants>
+    <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_HASHCODE;SUPPORTS_EXTENDED_INTRINSICS;SUPPORTS_SPAN_STREAM;SUPPORTS_ENCODING_STRING;SUPPORTS_CODECOVERAGE;SUPPORTS_BASE64SPAN</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp2.0'">
-    <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_CODECOVERAGE</DefineConstants>
+    <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_CODECOVERAGE;SUPPORTS_BASE64SPAN</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard2.1'">
     <DefineConstants>$(DefineConstants);SUPPORTS_MATHF;SUPPORTS_HASHCODE;SUPPORTS_SPAN_STREAM;SUPPORTS_ENCODING_STRING;SUPPORTS_CODECOVERAGE</DefineConstants>

src/ImageSharp/ImageExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
@@ -115,8 +116,25 @@ namespace SixLabors.ImageSharp
             using (var stream = new MemoryStream())
             {
                 source.Save(stream, format);
-                stream.Flush();
-                return $"data:{format.DefaultMimeType};base64,{Convert.ToBase64String(stream.ToArray())}";
+
+                // Always available.
+                stream.TryGetBuffer(out ArraySegment<byte> buffer);
+
+#if !SUPPORTS_BASE64SPAN
+
+                byte[] sharedBuffer = ArrayPool<byte>.Shared.Rent(buffer.Count);
+                try
+                {
+                    buffer.AsSpan().CopyTo(sharedBuffer);
+                    return $"data:{format.DefaultMimeType};base64,{Convert.ToBase64String(sharedBuffer)}";
+                }
+                finally
+                {
+                    ArrayPool<byte>.Shared.Return(sharedBuffer);
+                }
+#else
+                return $"data:{format.DefaultMimeType};base64,{Convert.ToBase64String(buffer)}";
+#endif
             }
         }
     }