No need to calculate CRC for non-critical chunks.

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -1141,19 +1141,22 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <param name="chunk">The <see cref="PngChunk"/>.</param>
         private void ValidateChunk(in PngChunk chunk)
         {
-            Span<byte> chunkType = stackalloc byte[4];
+            uint crc = this.ReadChunkCrc();
 
-            BinaryPrimitives.WriteUInt32BigEndian(chunkType, (uint)chunk.Type);
+            if (chunk.IsCritical)
+            {
+                Span<byte> chunkType = stackalloc byte[4];
+                BinaryPrimitives.WriteUInt32BigEndian(chunkType, (uint)chunk.Type);
 
-            this.crc.Reset();
-            this.crc.Update(chunkType);
-            this.crc.Update(chunk.Data.GetSpan());
+                this.crc.Reset();
+                this.crc.Update(chunkType);
+                this.crc.Update(chunk.Data.GetSpan());
 
-            uint crc = this.ReadChunkCrc();
-            if (this.crc.Value != crc && chunk.IsCritical)
-            {
-                string chunkTypeName = Encoding.ASCII.GetString(chunkType);
-                PngThrowHelper.ThrowInvalidChunkCrc(chunkTypeName);
+                if (this.crc.Value != crc)
+                {
+                    string chunkTypeName = Encoding.ASCII.GetString(chunkType);
+                    PngThrowHelper.ThrowInvalidChunkCrc(chunkTypeName);
+                }
             }
         }