/// <summary>
/// Encodes the provided BGRA pixel data to a 24bit BMP image.
/// </summary>
/// <param name="pixelData">The date to encode.</param>
/// <param name="width">The width of the image in the data.</param>
/// <param name="height">The height of the image in the data.</param>
/// <returns>A 24bit BMP image as bytes.</returns>
public static byte[] Encode(byte[] pixelData, int width, int height)
{
int rowWidth = width;
int amount = width * 3 % 4;
if (amount != 0)
{
rowWidth += 4 - amount;
}
int fileSize = BmpFileHeader.DEFAULT_OFFSET + height * rowWidth * 3;
var output = new byte[fileSize];
using (var writer = new BinaryWriter(new MemoryStream(output)))
{
var fileHeader = new BmpFileHeader
{
FileSize = fileSize,
Height = height,
Width = width,
BitsPerPixel = 24,
Planes = 1,
ImageSize = fileSize - BmpFileHeader.DEFAULT_OFFSET,
ClrUsed = 0,
ClrImportant = 0
};
writer.Write(fileHeader.Type);
writer.Write(fileHeader.FileSize);
writer.Write(fileHeader.Reserved);
writer.Write(fileHeader.Offset);
writer.Write(fileHeader.HeaderSize);
writer.Write(fileHeader.Width);
writer.Write(fileHeader.Height);
writer.Write(fileHeader.Planes);
writer.Write(fileHeader.BitsPerPixel);
writer.Write(fileHeader.Compression);
writer.Write(fileHeader.ImageSize);
writer.Write(fileHeader.XPelsPerMeter);
writer.Write(fileHeader.YPelsPerMeter);
writer.Write(fileHeader.ClrUsed);
writer.Write(fileHeader.ClrImportant);
if (amount != 0)
{
amount = 4 - amount;
}
for (int y = height - 1; y >= 0; y--)
{
for (var x = 0; x < width; x++)
{
int offset = (y * width + x) * 4;
writer.Write(pixelData[offset + 0]);
writer.Write(pixelData[offset + 1]);
writer.Write(pixelData[offset + 2]);
}
for (var i = 0; i < amount; i++)
{
writer.Write((byte)0);
}
}
}
return(output);
}
/// <summary>
/// Decode the provided bmp to a BGRA pixel array.
/// Supported formats are:
/// - 1, 4, and 8 bit BMP, tested with up to 256 colors.
/// - 16bit BMP (untested)
/// - 24bit BMP
/// - 32bit BMP (untested)
/// </summary>
/// <param name="bmpData">The bmp file as bytes to decode.</param>
/// <param name="fileHeader">The header of the file. Contains information such as the size of the image.</param>
/// <returns>An RGBA pixel array extracted from the BMP.</returns>
public static byte[] Decode(ReadOnlyMemory <byte> bmpData, out BmpFileHeader fileHeader)
{
using var reader = new ByteReader(bmpData);
fileHeader = new BmpFileHeader
{
Type = reader.ReadInt16(),
FileSize = reader.ReadInt32(),
Reserved = reader.ReadInt32(),
Offset = reader.ReadInt32(),
// Second header
HeaderSize = reader.ReadInt32(),
Width = reader.ReadInt32(),
Height = reader.ReadInt32(),
Planes = reader.ReadInt16(),
BitsPerPixel = reader.ReadInt16(),
Compression = reader.ReadInt32(),
ImageSize = reader.ReadInt32(),
XPelsPerMeter = reader.ReadInt32(),
YPelsPerMeter = reader.ReadInt32(),
ClrUsed = reader.ReadInt32(),
ClrImportant = reader.ReadInt32()
};
if (fileHeader.Compression != 0)
{
throw new Exception($"Unsupported BMP compression - {fileHeader.Compression}");
}
int colorMapSize = -1;
if (fileHeader.ClrUsed == 0)
{
if (fileHeader.BitsPerPixel == 1 ||
fileHeader.BitsPerPixel == 4 ||
fileHeader.BitsPerPixel == 8)
{
colorMapSize = (int)Math.Pow(2, fileHeader.BitsPerPixel) * 4;
}
}
else
{
colorMapSize = fileHeader.ClrUsed * 4;
}
ReadOnlySpan <byte> palette = null;
if (colorMapSize > 0)
{
palette = reader.ReadBytes(colorMapSize);
}
ReadOnlySpan <byte> pixelIn = reader.ReadBytes(fileHeader.ImageSize);
var pixelOut = new byte[fileHeader.Width * fileHeader.Height * 4];
if (fileHeader.HeaderSize != 40)
{
throw new Exception(
$"Header Size value '{fileHeader.HeaderSize}' is not valid.");
}
if (fileHeader.BitsPerPixel == 32)
{
ReadRgb32(pixelIn, pixelOut, fileHeader.Width, fileHeader.Height);
}
else if (fileHeader.BitsPerPixel == 24)
{
ReadRgb24(pixelIn, pixelOut, fileHeader.Width, fileHeader.Height);
}
else if (fileHeader.BitsPerPixel == 16)
{
ReadRgb16(pixelIn, pixelOut, fileHeader.Width, fileHeader.Height);
}
else if (fileHeader.BitsPerPixel <= 8)
{
ReadRgbPalette(
pixelIn,
pixelOut,
palette,
fileHeader.Width,
fileHeader.Height,
fileHeader.BitsPerPixel);
}
return(pixelOut);
}
