Update PngDecoder.cs

src/ImageSharp/Formats/Png/PngDecoder.cs

@@ -31,39 +31,82 @@ namespace SixLabors.ImageSharp.Formats.Png
             IImageInfo info = decoder.Identify(configuration, stream);
             stream.Position = 0;
 
-            switch (info.Metadata.GetPngMetadata().ColorType)
+            PngMetadata meta = info.Metadata.GetPngMetadata();
+            PngColorType color = meta.ColorType.GetValueOrDefault();
+            PngBitDepth bits = meta.BitDepth.GetValueOrDefault();
+            return color switch
             {
-                default:
-                    break;
-            }
+                PngColorType.Grayscale => (bits == PngBitDepth.Bit16)
+                ? this.Decode<L16>(configuration, stream)
+                : this.Decode<L8>(configuration, stream),
 
-            return this.Decode<Rgba32>(configuration, stream);
+                PngColorType.Rgb => this.Decode<Rgb24>(configuration, stream),
+
+                PngColorType.Palette => this.Decode<Rgba32>(configuration, stream),
+
+                PngColorType.GrayscaleWithAlpha => (bits == PngBitDepth.Bit16)
+                ? this.Decode<La32>(configuration, stream)
+                : this.Decode<La16>(configuration, stream),
+
+                PngColorType.RgbWithAlpha => (bits == PngBitDepth.Bit16)
+                ? this.Decode<Rgba64>(configuration, stream)
+                : this.Decode<Rgba32>(configuration, stream),
+
+                _ => this.Decode<Rgba32>(configuration, stream),
+            };
         }
 
         /// <inheritdoc/>
         public Task<Image<TPixel>> DecodeAsync<TPixel>(Configuration configuration, Stream stream, CancellationToken cancellationToken)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var decoder = new PngDecoderCore(configuration, this);
+            PngDecoderCore decoder = new(configuration, this);
             return decoder.DecodeAsync<TPixel>(configuration, stream, cancellationToken);
         }
 
         /// <inheritdoc />
         public async Task<Image> DecodeAsync(Configuration configuration, Stream stream, CancellationToken cancellationToken)
-            => await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken)
-            .ConfigureAwait(false);
+        {
+            PngDecoderCore decoder = new(configuration, true);
+            IImageInfo info = await decoder.IdentifyAsync(configuration, stream, cancellationToken).ConfigureAwait(false);
+            stream.Position = 0;
+
+            PngMetadata meta = info.Metadata.GetPngMetadata();
+            PngColorType color = meta.ColorType.GetValueOrDefault();
+            PngBitDepth bits = meta.BitDepth.GetValueOrDefault();
+            return color switch
+            {
+                PngColorType.Grayscale => (bits == PngBitDepth.Bit16)
+                ? await this.DecodeAsync<L16>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                : await this.DecodeAsync<L8>(configuration, stream, cancellationToken).ConfigureAwait(false),
+
+                PngColorType.Rgb => await this.DecodeAsync<Rgb24>(configuration, stream, cancellationToken).ConfigureAwait(false),
+
+                PngColorType.Palette => await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken).ConfigureAwait(false),
+
+                PngColorType.GrayscaleWithAlpha => (bits == PngBitDepth.Bit16)
+                ? await this.DecodeAsync<La32>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                : await this.DecodeAsync<La16>(configuration, stream, cancellationToken).ConfigureAwait(false),
+
+                PngColorType.RgbWithAlpha => (bits == PngBitDepth.Bit16)
+                ? await this.DecodeAsync<Rgba64>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                : await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken).ConfigureAwait(false),
+
+                _ => await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken).ConfigureAwait(false),
+            };
+        }
 
         /// <inheritdoc/>
         public IImageInfo Identify(Configuration configuration, Stream stream)
         {
-            var decoder = new PngDecoderCore(configuration, this);
+            PngDecoderCore decoder = new(configuration, this);
             return decoder.Identify(configuration, stream);
         }
 
         /// <inheritdoc/>
         public Task<IImageInfo> IdentifyAsync(Configuration configuration, Stream stream, CancellationToken cancellationToken)
         {
-            var decoder = new PngDecoderCore(configuration, this);
+            PngDecoderCore decoder = new(configuration, this);
             return decoder.IdentifyAsync(configuration, stream, cancellationToken);
         }
     }