/// <summary>
/// Reads the raw image information from the specified stream.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing image data.</param>
public IImageInfo Identify(Stream stream)
{
var metaData = new ImageMetaData();
PngMetaData pngMetaData = metaData.GetFormatMetaData(PngFormat.Instance);
this.currentStream = stream;
this.currentStream.Skip(8);
try
{
while (!this.isEndChunkReached && this.TryReadChunk(out PngChunk chunk))
{
try
{
switch (chunk.Type)
{
case PngChunkType.Header:
this.ReadHeaderChunk(pngMetaData, chunk.Data.Array);
break;
case PngChunkType.Physical:
this.ReadPhysicalChunk(metaData, chunk.Data.GetSpan());
break;
case PngChunkType.Gamma:
this.ReadGammaChunk(pngMetaData, chunk.Data.GetSpan());
break;
case PngChunkType.Data:
this.SkipChunkDataAndCrc(chunk);
break;
case PngChunkType.Text:
this.ReadTextChunk(metaData, chunk.Data.Array.AsSpan(0, chunk.Length));
break;
case PngChunkType.End:
this.isEndChunkReached = true;
break;
}
}
finally
{
chunk.Data?.Dispose(); // Data is rented in ReadChunkData()
}
}
}
finally
{
this.scanline?.Dispose();
this.previousScanline?.Dispose();
}
if (this.header.Width == 0 && this.header.Height == 0)
{
throw new ImageFormatException("PNG Image does not contain a header chunk");
}
return(new ImageInfo(new PixelTypeInfo(this.CalculateBitsPerPixel()), this.header.Width, this.header.Height, metaData));
}
/// <summary>
/// Initializes a new instance of the <see cref="PngMetaData"/> class.
/// </summary>
/// <param name="other">The metadata to create an instance from.</param>
private PngMetaData(PngMetaData other)
{
this.BitDepth = other.BitDepth;
this.ColorType = other.ColorType;
this.Gamma = other.Gamma;
this.HasTrans = other.HasTrans;
this.TransparentGray8 = other.TransparentGray8;
this.TransparentGray16 = other.TransparentGray16;
this.TransparentRgb24 = other.TransparentRgb24;
this.TransparentRgb48 = other.TransparentRgb48;
}
/// <summary>
/// Decodes the stream to the image.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="stream">The stream containing image data. </param>
/// <exception cref="ImageFormatException">
/// Thrown if the stream does not contain and end chunk.
/// </exception>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown if the image is larger than the maximum allowable size.
/// </exception>
/// <returns>The decoded image</returns>
public Image <TPixel> Decode <TPixel>(Stream stream)
where TPixel : struct, IPixel <TPixel>
{
var metaData = new ImageMetaData();
PngMetaData pngMetaData = metaData.GetFormatMetaData(PngFormat.Instance);
this.currentStream = stream;
this.currentStream.Skip(8);
Image <TPixel> image = null;
try
{
while (!this.isEndChunkReached && this.TryReadChunk(out PngChunk chunk))
{
try
{
switch (chunk.Type)
{
case PngChunkType.Header:
this.ReadHeaderChunk(pngMetaData, chunk.Data.Array);
break;
case PngChunkType.Physical:
this.ReadPhysicalChunk(metaData, chunk.Data.GetSpan());
break;
case PngChunkType.Gamma:
this.ReadGammaChunk(pngMetaData, chunk.Data.GetSpan());
break;
case PngChunkType.Data:
if (image is null)
{
this.InitializeImage(metaData, out image);
}
using (var deframeStream = new ZlibInflateStream(this.currentStream, this.ReadNextDataChunk))
{
deframeStream.AllocateNewBytes(chunk.Length);
this.ReadScanlines(deframeStream.CompressedStream, image.Frames.RootFrame, pngMetaData);
}
break;
case PngChunkType.Palette:
byte[] pal = new byte[chunk.Length];
Buffer.BlockCopy(chunk.Data.Array, 0, pal, 0, chunk.Length);
this.palette = pal;
break;
case PngChunkType.Transparency:
byte[] alpha = new byte[chunk.Length];
Buffer.BlockCopy(chunk.Data.Array, 0, alpha, 0, chunk.Length);
this.paletteAlpha = alpha;
this.AssignTransparentMarkers(alpha, pngMetaData);
break;
case PngChunkType.Text:
this.ReadTextChunk(metaData, chunk.Data.Array.AsSpan(0, chunk.Length));
break;
case PngChunkType.Exif:
if (!this.ignoreMetadata)
{
byte[] exifData = new byte[chunk.Length];
Buffer.BlockCopy(chunk.Data.Array, 0, exifData, 0, chunk.Length);
metaData.ExifProfile = new ExifProfile(exifData);
}
break;
case PngChunkType.End:
this.isEndChunkReached = true;
break;
}
}
finally
{
chunk.Data?.Dispose(); // Data is rented in ReadChunkData()
}
}
if (image is null)
{
throw new ImageFormatException("PNG Image does not contain a data chunk");
}
return(image);
}
finally
{
this.scanline?.Dispose();
this.previousScanline?.Dispose();
}
}
/// <summary>
/// Encodes the image to the specified stream from the <see cref="Image{TPixel}"/>.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="stream">The <see cref="Stream"/> to encode the image data to.</param>
public void Encode <TPixel>(Image <TPixel> image, Stream stream)
where TPixel : struct, IPixel <TPixel>
{
Guard.NotNull(image, nameof(image));
Guard.NotNull(stream, nameof(stream));
this.width = image.Width;
this.height = image.Height;
// Always take the encoder options over the metadata values.
ImageMetaData metaData = image.MetaData;
PngMetaData pngMetaData = metaData.GetFormatMetaData(PngFormat.Instance);
this.gamma = this.gamma ?? pngMetaData.Gamma;
this.writeGamma = this.gamma > 0;
this.pngColorType = this.pngColorType ?? pngMetaData.ColorType;
this.pngBitDepth = this.pngBitDepth ?? pngMetaData.BitDepth;
this.use16Bit = this.pngBitDepth.Equals(PngBitDepth.Bit16);
stream.Write(PngConstants.HeaderBytes, 0, PngConstants.HeaderBytes.Length);
QuantizedFrame <TPixel> quantized = null;
ReadOnlySpan <byte> quantizedPixelsSpan = default;
if (this.pngColorType == PngColorType.Palette)
{
byte bits;
// Use the metadata to determine what quantization depth to use if no quantizer has been set.
if (this.quantizer == null)
{
bits = (byte)Math.Min(8u, (short)this.pngBitDepth);
int colorSize = ImageMaths.GetColorCountForBitDepth(bits);
this.quantizer = new WuQuantizer(colorSize);
}
// Create quantized frame returning the palette and set the bit depth.
quantized = this.quantizer.CreateFrameQuantizer <TPixel>().QuantizeFrame(image.Frames.RootFrame);
quantizedPixelsSpan = quantized.GetPixelSpan();
bits = (byte)ImageMaths.GetBitsNeededForColorDepth(quantized.Palette.Length).Clamp(1, 8);
// Png only supports in four pixel depths: 1, 2, 4, and 8 bits when using the PLTE chunk
if (bits == 3)
{
bits = 4;
}
else if (bits >= 5 && bits <= 7)
{
bits = 8;
}
this.bitDepth = bits;
}
else
{
this.bitDepth = (byte)(this.use16Bit ? 16 : 8);
}
this.bytesPerPixel = this.CalculateBytesPerPixel();
var header = new PngHeader(
width: image.Width,
height: image.Height,
bitDepth: this.bitDepth,
colorType: this.pngColorType.Value,
compressionMethod: 0, // None
filterMethod: 0,
interlaceMethod: 0); // TODO: Can't write interlaced yet.
this.WriteHeaderChunk(stream, header);
// Collect the indexed pixel data
if (quantized != null)
{
this.WritePaletteChunk(stream, header, quantized);
}
this.WritePhysicalChunk(stream, metaData);
this.WriteGammaChunk(stream);
this.WriteExifChunk(stream, metaData);
this.WriteDataChunks(image.Frames.RootFrame, quantizedPixelsSpan, stream);
this.WriteEndChunk(stream);
stream.Flush();
quantized?.Dispose();
}
/// <summary>
/// Encodes the image to the specified stream from the <see cref="Image{TPixel}"/>.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The <see cref="ImageFrame{TPixel}"/> to encode from.</param>
/// <param name="stream">The <see cref="Stream"/> to encode the image data to.</param>
public void Encode <TPixel>(Image <TPixel> image, Stream stream)
where TPixel : struct, IPixel <TPixel>
{
Guard.NotNull(image, nameof(image));
Guard.NotNull(stream, nameof(stream));
this.configuration = image.GetConfiguration();
this.width = image.Width;
this.height = image.Height;
// Always take the encoder options over the metadata values.
ImageMetaData metaData = image.MetaData;
PngMetaData pngMetaData = metaData.GetFormatMetaData(PngFormat.Instance);
this.gamma = this.gamma ?? pngMetaData.Gamma;
this.writeGamma = this.gamma > 0;
this.pngColorType = this.pngColorType ?? pngMetaData.ColorType;
this.pngBitDepth = this.pngBitDepth ?? pngMetaData.BitDepth;
this.use16Bit = this.pngBitDepth.Equals(PngBitDepth.Bit16);
// Ensure we are not allowing impossible combinations.
if (!ColorTypes.ContainsKey(this.pngColorType.Value))
{
throw new NotSupportedException("Color type is not supported or not valid.");
}
stream.Write(PngConstants.HeaderBytes, 0, PngConstants.HeaderBytes.Length);
QuantizedFrame <TPixel> quantized = null;
if (this.pngColorType == PngColorType.Palette)
{
byte bits = (byte)this.pngBitDepth;
if (!ColorTypes[this.pngColorType.Value].Contains(bits))
{
throw new NotSupportedException("Bit depth is not supported or not valid.");
}
// Use the metadata to determine what quantization depth to use if no quantizer has been set.
if (this.quantizer == null)
{
this.quantizer = new WuQuantizer(ImageMaths.GetColorCountForBitDepth(bits));
}
// Create quantized frame returning the palette and set the bit depth.
quantized = this.quantizer.CreateFrameQuantizer <TPixel>(image.GetConfiguration())
.QuantizeFrame(image.Frames.RootFrame);
byte quantizedBits = (byte)ImageMaths.GetBitsNeededForColorDepth(quantized.Palette.Length).Clamp(1, 8);
bits = Math.Max(bits, quantizedBits);
// Png only supports in four pixel depths: 1, 2, 4, and 8 bits when using the PLTE chunk
// We check again for the bit depth as the bit depth of the color palette from a given quantizer might not
// be within the acceptable range.
if (bits == 3)
{
bits = 4;
}
else if (bits >= 5 && bits <= 7)
{
bits = 8;
}
this.bitDepth = bits;
}
else
{
this.bitDepth = (byte)this.pngBitDepth;
if (!ColorTypes[this.pngColorType.Value].Contains(this.bitDepth))
{
throw new NotSupportedException("Bit depth is not supported or not valid.");
}
}
this.bytesPerPixel = this.CalculateBytesPerPixel();
var header = new PngHeader(
width: image.Width,
height: image.Height,
bitDepth: this.bitDepth,
colorType: this.pngColorType.Value,
compressionMethod: 0, // None
filterMethod: 0,
interlaceMethod: 0); // TODO: Can't write interlaced yet.
this.WriteHeaderChunk(stream, header);
// Collect the indexed pixel data
if (quantized != null)
{
this.WritePaletteChunk(stream, quantized);
}
this.WritePhysicalChunk(stream, metaData);
this.WriteGammaChunk(stream);
this.WriteExifChunk(stream, metaData);
this.WriteDataChunks(image.Frames.RootFrame, quantized, stream);
this.WriteEndChunk(stream);
stream.Flush();
quantized?.Dispose();
}