/// <summary>
/// Encode writes the image to the jpeg baseline format with the given options.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The image to write from.</param>
/// <param name="stream">The stream to write to.</param>
public void Encode <TPixel>(Image <TPixel> image, Stream stream)
where TPixel : unmanaged, IPixel <TPixel>
{
Guard.NotNull(image, nameof(image));
Guard.NotNull(stream, nameof(stream));
const ushort max = JpegConstants.MaxLength;
if (image.Width >= max || image.Height >= max)
{
throw new ImageFormatException($"Image is too large to encode at {image.Width}x{image.Height}.");
}
this.outputStream = stream;
ImageMetadata metadata = image.Metadata;
// System.Drawing produces identical output for jpegs with a quality parameter of 0 and 1.
int qlty = (this.quality ?? metadata.GetJpegMetadata().Quality).Clamp(1, 100);
this.subsample = this.subsample ?? (qlty >= 91 ? JpegSubsample.Ratio444 : JpegSubsample.Ratio420);
// Convert from a quality rating to a scaling factor.
int scale;
if (qlty < 50)
{
scale = 5000 / qlty;
}
else
{
scale = 200 - (qlty * 2);
}
// Initialize the quantization tables.
InitQuantizationTable(0, scale, ref this.luminanceQuantTable);
InitQuantizationTable(1, scale, ref this.chrominanceQuantTable);
// Compute number of components based on input image type.
const int componentCount = 3;
// Write the Start Of Image marker.
this.WriteApplicationHeader(metadata);
// Write Exif, ICC and IPTC profiles
this.WriteProfiles(metadata);
// Write the quantization tables.
this.WriteDefineQuantizationTables();
// Write the image dimensions.
this.WriteStartOfFrame(image.Width, image.Height, componentCount);
// Write the Huffman tables.
this.WriteDefineHuffmanTables(componentCount);
// Write the image data.
this.WriteStartOfScan(image);
// Write the End Of Image marker.
this.buffer[0] = JpegConstants.Markers.XFF;
this.buffer[1] = JpegConstants.Markers.EOI;
stream.Write(this.buffer, 0, 2);
stream.Flush();
}
/// <summary>
/// Encode writes the image to the jpeg baseline format with the given options.
/// </summary>
/// <typeparam name="TPixel">The pixel format.</typeparam>
/// <param name="image">The image to write from.</param>
/// <param name="stream">The stream to write to.</param>
/// <param name="cancellationToken">The token to request cancellation.</param>
public void Encode <TPixel>(Image <TPixel> image, Stream stream, CancellationToken cancellationToken)
where TPixel : unmanaged, IPixel <TPixel>
{
Guard.NotNull(image, nameof(image));
Guard.NotNull(stream, nameof(stream));
if (image.Width >= JpegConstants.MaxLength || image.Height >= JpegConstants.MaxLength)
{
JpegThrowHelper.ThrowDimensionsTooLarge(image.Width, image.Height);
}
cancellationToken.ThrowIfCancellationRequested();
this.outputStream = stream;
ImageMetadata metadata = image.Metadata;
JpegMetadata jpegMetadata = metadata.GetJpegMetadata();
// If the color type was not specified by the user, preserve the color type of the input image.
if (!this.colorType.HasValue)
{
this.colorType = GetFallbackColorType(image);
}
// Compute number of components based on color type in options.
int componentCount = (this.colorType == JpegColorType.Luminance) ? 1 : 3;
ReadOnlySpan <byte> componentIds = this.GetComponentIds();
// TODO: Right now encoder writes both quantization tables for grayscale images - we shouldn't do that
// Initialize the quantization tables.
this.InitQuantizationTables(componentCount, jpegMetadata, out Block8x8F luminanceQuantTable, out Block8x8F chrominanceQuantTable);
// Write the Start Of Image marker.
this.WriteStartOfImage();
// Do not write APP0 marker for RGB colorspace.
if (this.colorType != JpegColorType.Rgb)
{
this.WriteJfifApplicationHeader(metadata);
}
// Write Exif, XMP, ICC and IPTC profiles
this.WriteProfiles(metadata);
if (this.colorType == JpegColorType.Rgb)
{
// Write App14 marker to indicate RGB color space.
this.WriteApp14Marker();
}
// Write the quantization tables.
this.WriteDefineQuantizationTables(ref luminanceQuantTable, ref chrominanceQuantTable);
// Write the image dimensions.
this.WriteStartOfFrame(image.Width, image.Height, componentCount, componentIds);
// Write the Huffman tables.
this.WriteDefineHuffmanTables(componentCount);
// Write the scan header.
this.WriteStartOfScan(componentCount, componentIds);
// Write the scan compressed data.
switch (this.colorType)
{
case JpegColorType.YCbCrRatio444:
new HuffmanScanEncoder(3, stream).Encode444(image, ref luminanceQuantTable, ref chrominanceQuantTable, cancellationToken);
break;
case JpegColorType.YCbCrRatio420:
new HuffmanScanEncoder(6, stream).Encode420(image, ref luminanceQuantTable, ref chrominanceQuantTable, cancellationToken);
break;
case JpegColorType.Luminance:
new HuffmanScanEncoder(1, stream).EncodeGrayscale(image, ref luminanceQuantTable, cancellationToken);
break;
case JpegColorType.Rgb:
new HuffmanScanEncoder(3, stream).EncodeRgb(image, ref luminanceQuantTable, cancellationToken);
break;
default:
// all other non-supported color types are checked at the start of this method
break;
}
// Write the End Of Image marker.
this.WriteEndOfImageMarker();
stream.Flush();
}
