/// <summary>
/// Reads the tga file header from the stream.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing image data.</param>
/// <returns>The image origin.</returns>
private TgaImageOrigin ReadFileHeader(Stream stream)
{
this.currentStream = stream;
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
this.currentStream.Read(buffer, 0, TgaFileHeader.Size);
this.fileHeader = TgaFileHeader.Parse(buffer);
this.metadata = new ImageMetadata();
this.tgaMetadata = this.metadata.GetTgaMetadata();
this.tgaMetadata.BitsPerPixel = (TgaBitsPerPixel)this.fileHeader.PixelDepth;
var alphaBits = this.fileHeader.ImageDescriptor & 0xf;
if (alphaBits != 0 && alphaBits != 1 && alphaBits != 8)
{
TgaThrowHelper.ThrowImageFormatException("Invalid alpha channel bits");
}
this.tgaMetadata.AlphaChannelBits = (byte)alphaBits;
this.hasAlpha = alphaBits > 0;
// Bits 4 and 5 describe the image origin.
var origin = (TgaImageOrigin)((this.fileHeader.ImageDescriptor & 0x30) >> 4);
return(origin);
}
/// <summary>
/// Reads the tga file header from the stream.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing image data.</param>
/// <returns>true, if the image origin is top left.</returns>
private bool ReadFileHeader(Stream stream)
{
this.currentStream = stream;
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
this.currentStream.Read(buffer, 0, TgaFileHeader.Size);
this.fileHeader = TgaFileHeader.Parse(buffer);
this.metadata = new ImageMetadata();
this.tgaMetadata = this.metadata.GetTgaMetadata();
this.tgaMetadata.BitsPerPixel = (TgaBitsPerPixel)this.fileHeader.PixelDepth;
var alphaBits = this.fileHeader.ImageDescriptor & 0xf;
if (alphaBits != 0 && alphaBits != 1 && alphaBits != 8)
{
TgaThrowHelper.ThrowImageFormatException("Invalid alpha channel bits");
}
this.tgaMetadata.AlphaChannelBits = (byte)alphaBits;
this.hasAlpha = alphaBits > 0;
// TODO: bits 4 and 5 describe the image origin. See spec page 9. bit 4 is currently ignored.
// Theoretically the origin could also be top right and bottom right.
// Bit at position 5 of the descriptor indicates, that the origin is top left instead of bottom left.
if ((this.fileHeader.ImageDescriptor & (1 << 5)) != 0)
{
return(true);
}
return(false);
}
/// <summary>
/// Encodes the image to the specified stream from the <see cref="ImageFrame{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();
ImageMetadata metadata = image.Metadata;
TgaMetadata tgaMetadata = metadata.GetFormatMetadata(TgaFormat.Instance);
this.bitsPerPixel = this.bitsPerPixel ?? tgaMetadata.BitsPerPixel;
TgaImageType imageType = this.compression is TgaCompression.RunLength ? TgaImageType.RleTrueColor : TgaImageType.TrueColor;
if (this.bitsPerPixel == TgaBitsPerPixel.Pixel8)
{
imageType = this.compression is TgaCompression.RunLength ? TgaImageType.RleBlackAndWhite : TgaImageType.BlackAndWhite;
}
// If compression is used, set bit 5 of the image descriptor to indicate an left top origin.
byte imageDescriptor = (byte)(this.compression is TgaCompression.RunLength ? 32 : 0);
var fileHeader = new TgaFileHeader(
idLength: 0,
colorMapType: 0,
imageType: imageType,
cMapStart: 0,
cMapLength: 0,
cMapDepth: 0,
xOffset: 0,
yOffset: this.compression is TgaCompression.RunLength ? (short)image.Height : (short)0, // When run length encoding is used, the origin should be top left instead of the default bottom left.
width: (short)image.Width,
height: (short)image.Height,
pixelDepth: (byte)this.bitsPerPixel.Value,
imageDescriptor: imageDescriptor);
#if NETCOREAPP2_1
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
#else
byte[] buffer = new byte[TgaFileHeader.Size];
#endif
fileHeader.WriteTo(buffer);
stream.Write(buffer, 0, TgaFileHeader.Size);
if (this.compression is TgaCompression.RunLength)
{
this.WriteRunLengthEndcodedImage(stream, image.Frames.RootFrame);
}
else
{
this.WriteImage(stream, image.Frames.RootFrame);
}
stream.Flush();
}
/// <summary>
/// Reads the tga file header from the stream.
/// </summary>
/// <param name="stream">The <see cref="Stream"/> containing image data.</param>
/// <returns>true, if the image origin is top left.</returns>
private bool ReadFileHeader(Stream stream)
{
this.currentStream = stream;
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
this.currentStream.Read(buffer, 0, TgaFileHeader.Size);
this.fileHeader = TgaFileHeader.Parse(buffer);
this.metadata = new ImageMetadata();
this.tgaMetadata = this.metadata.GetTgaMetadata();
this.tgaMetadata.BitsPerPixel = (TgaBitsPerPixel)this.fileHeader.PixelDepth;
// Bit at position 5 of the descriptor indicates, that the origin is top left instead of bottom right.
if ((this.fileHeader.ImageDescriptor & (1 << 5)) != 0)
{
return(true);
}
return(false);
}
/// <summary>
/// Encodes the image to the specified stream from the <see cref="ImageFrame{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 : unmanaged, IPixel <TPixel>
{
Guard.NotNull(image, nameof(image));
Guard.NotNull(stream, nameof(stream));
this.configuration = image.GetConfiguration();
ImageMetadata metadata = image.Metadata;
TgaMetadata tgaMetadata = metadata.GetTgaMetadata();
this.bitsPerPixel = this.bitsPerPixel ?? tgaMetadata.BitsPerPixel;
TgaImageType imageType = this.compression is TgaCompression.RunLength ? TgaImageType.RleTrueColor : TgaImageType.TrueColor;
if (this.bitsPerPixel == TgaBitsPerPixel.Pixel8)
{
imageType = this.compression is TgaCompression.RunLength ? TgaImageType.RleBlackAndWhite : TgaImageType.BlackAndWhite;
}
byte imageDescriptor = 0;
if (this.compression is TgaCompression.RunLength)
{
// If compression is used, set bit 5 of the image descriptor to indicate a left top origin.
imageDescriptor |= 0x20;
}
if (this.bitsPerPixel is TgaBitsPerPixel.Pixel32)
{
// Indicate, that 8 bit are used for the alpha channel.
imageDescriptor |= 0x8;
}
if (this.bitsPerPixel is TgaBitsPerPixel.Pixel16)
{
// Indicate, that 1 bit is used for the alpha channel.
imageDescriptor |= 0x1;
}
var fileHeader = new TgaFileHeader(
idLength: 0,
colorMapType: 0,
imageType: imageType,
cMapStart: 0,
cMapLength: 0,
cMapDepth: 0,
xOffset: 0,
yOffset: this.compression is TgaCompression.RunLength ? (short)image.Height : (short)0, // When run length encoding is used, the origin should be top left instead of the default bottom left.
width: (short)image.Width,
height: (short)image.Height,
pixelDepth: (byte)this.bitsPerPixel.Value,
imageDescriptor: imageDescriptor);
Span <byte> buffer = stackalloc byte[TgaFileHeader.Size];
fileHeader.WriteTo(buffer);
stream.Write(buffer, 0, TgaFileHeader.Size);
if (this.compression is TgaCompression.RunLength)
{
this.WriteRunLengthEncodedImage(stream, image.Frames.RootFrame);
}
else
{
this.WriteImage(stream, image.Frames.RootFrame);
}
stream.Flush();
}
