Merge pull request #1861 from SixLabors/js/png-decode-to-type

Png - Preserve Pixel Format for Non-generic decode.
SixLabors · Dec 14, 2021 · ecd3db2 · ecd3db2
2 parents 82e8c0d + f6b8383
commit ecd3db2
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Showing 3 changed files with 320 additions and 163 deletions.
diff --git a/src/ImageSharp/Formats/Png/PngDecoder.cs b/src/ImageSharp/Formats/Png/PngDecoder.cs
@@ -20,37 +20,137 @@ public sealed class PngDecoder : IImageDecoder, IPngDecoderOptions, IImageInfoDe
         public Image<TPixel> Decode<TPixel>(Configuration configuration, Stream stream)
             where TPixel : unmanaged, IPixel<TPixel>
         {
-            var decoder = new PngDecoderCore(configuration, this);
+            PngDecoderCore decoder = new(configuration, this);
             return decoder.Decode<TPixel>(configuration, stream);
         }
 
         /// <inheritdoc />
-        public Image Decode(Configuration configuration, Stream stream) => this.Decode<Rgba32>(configuration, stream);
+        public Image Decode(Configuration configuration, Stream stream)
+        {
+            PngDecoderCore decoder = new(configuration, true);
+            IImageInfo info = decoder.Identify(configuration, stream);
+            stream.Position = 0;
+
+            PngMetadata meta = info.Metadata.GetPngMetadata();
+            PngColorType color = meta.ColorType.GetValueOrDefault();
+            PngBitDepth bits = meta.BitDepth.GetValueOrDefault();
+            switch (color)
+            {
+                case PngColorType.Grayscale:
+                    if (bits == PngBitDepth.Bit16)
+                    {
+                        return !meta.HasTransparency
+                            ? this.Decode<L16>(configuration, stream)
+                            : this.Decode<La32>(configuration, stream);
+                    }
+
+                    return !meta.HasTransparency
+                        ? this.Decode<L8>(configuration, stream)
+                        : this.Decode<La16>(configuration, stream);
+
+                case PngColorType.Rgb:
+                    if (bits == PngBitDepth.Bit16)
+                    {
+                        return !meta.HasTransparency
+                            ? this.Decode<Rgb48>(configuration, stream)
+                            : this.Decode<Rgba64>(configuration, stream);
+                    }
+
+                    return !meta.HasTransparency
+                        ? this.Decode<Rgb24>(configuration, stream)
+                        : this.Decode<Rgba32>(configuration, stream);
+
+                case PngColorType.Palette:
+                    return this.Decode<Rgba32>(configuration, stream);
+
+                case PngColorType.GrayscaleWithAlpha:
+                    return (bits == PngBitDepth.Bit16)
+                    ? this.Decode<La32>(configuration, stream)
+                    : this.Decode<La16>(configuration, stream);
+
+                case PngColorType.RgbWithAlpha:
+                    return (bits == PngBitDepth.Bit16)
+                    ? this.Decode<Rgba64>(configuration, stream)
+                    : this.Decode<Rgba32>(configuration, stream);
+
+                default:
+                    return 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();
+            switch (color)
+            {
+                case PngColorType.Grayscale:
+                    if (bits == PngBitDepth.Bit16)
+                    {
+                        return !meta.HasTransparency
+                            ? await this.DecodeAsync<L16>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                            : await this.DecodeAsync<La32>(configuration, stream, cancellationToken).ConfigureAwait(false);
+                    }
+
+                    return !meta.HasTransparency
+                        ? await this.DecodeAsync<L8>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                        : await this.DecodeAsync<La16>(configuration, stream, cancellationToken).ConfigureAwait(false);
+
+                case PngColorType.Rgb:
+                    if (bits == PngBitDepth.Bit16)
+                    {
+                        return !meta.HasTransparency
+                            ? await this.DecodeAsync<Rgb48>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                            : await this.DecodeAsync<Rgba64>(configuration, stream, cancellationToken).ConfigureAwait(false);
+                    }
+
+                    return !meta.HasTransparency
+                        ? await this.DecodeAsync<Rgb24>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                        : await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken).ConfigureAwait(false);
+
+                case PngColorType.Palette:
+                    return await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken).ConfigureAwait(false);
+
+                case PngColorType.GrayscaleWithAlpha:
+                    return (bits == PngBitDepth.Bit16)
+                        ? await this.DecodeAsync<La32>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                        : await this.DecodeAsync<La16>(configuration, stream, cancellationToken).ConfigureAwait(false);
+
+                case PngColorType.RgbWithAlpha:
+                    return (bits == PngBitDepth.Bit16)
+                        ? await this.DecodeAsync<Rgba64>(configuration, stream, cancellationToken).ConfigureAwait(false)
+                        : await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken).ConfigureAwait(false);
+
+                default:
+                    return 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);
         }
     }