// Load a PNG image from the specified stream. The first 4 bytes
// have already been read and discarded.
public static void Load(Stream stream, Image image)
{
byte[] buffer = new byte [1024];
int width = 0;
int height = 0;
int bitDepth = 0;
int colorType = 0;
int compressionMethod = 0;
int filterMethod = 0;
int interlaceMethod = 0;
Frame frame = null;
PixelFormat format = 0;
int index;
int significant = 0;
ZlibDecompressor decompress = null;
ScanlineReader scanlineReader;
int pass, passWidth, passHeight;
PassFunc passFunc;
// Read the rest of the magic number and check it.
if(stream.Read(buffer, 0, 4) != 4)
{
throw new FormatException("could not read magic number");
}
if(buffer[0] != (byte)13 ||
buffer[1] != (byte)10 ||
buffer[2] != (byte)26 ||
buffer[3] != (byte)10)
{
throw new FormatException("invalid magic number");
}
// Create a chunk reader for the stream.
ChunkReader reader = new ChunkReader(stream, buffer);
// Read all of the chunks from the stream.
while(reader.Type != IEND)
{
// Process the critical chunk types.
if(reader.Type == IHDR)
{
// We can only have one header per PNG image.
if(image.NumFrames > 0)
{
throw new FormatException("multiple headers");
}
// Read the contents of the image header.
if(reader.Read(buffer, 0, 13) != 13)
{
throw new FormatException("truncated header");
}
width = Utils.ReadInt32B(buffer, 0);
height = Utils.ReadInt32B(buffer, 4);
bitDepth = buffer[8];
colorType = buffer[9];
compressionMethod = buffer[10];
filterMethod = buffer[11];
interlaceMethod = buffer[12];
// Sanity-check the values.
if(width < 1 || height < 1)
{
throw new FormatException("invalid size");
}
if(colorType == 0)
{
if(bitDepth != 1 && bitDepth != 2 &&
bitDepth != 4 && bitDepth != 8 &&
bitDepth != 16)
{
throw new FormatException
("invalid depth for color type 0");
}
}
else if(colorType == 2 || colorType == 4 ||
colorType == 6)
{
if(bitDepth != 8 && bitDepth != 16)
{
throw new FormatException
("invalid depth for color type " +
colorType.ToString());
}
}
else if(colorType == 3)
{
if(bitDepth != 1 && bitDepth != 2 &&
bitDepth != 4 && bitDepth != 8)
{
throw new FormatException
("invalid depth for color type 3");
}
}
else
{
throw new FormatException("invalid color type");
}
if(compressionMethod != 0)
{
throw new FormatException
("invalid compression method");
}
if(filterMethod != 0)
{
throw new FormatException
("invalid filter method");
}
if(interlaceMethod != 0 && interlaceMethod != 1)
{
throw new FormatException
("invalid interlace method");
}
// Create the image frame with the requested values.
if(colorType == 3)
{
format = PixelFormat.Format8bppIndexed;
}
else if((colorType & 4) != 0)
{
if(significant == 0x01050505 && bitDepth == 8)
{
format = PixelFormat.Format16bppArgb1555;
}
else if(bitDepth == 8)
{
format = PixelFormat.Format32bppArgb;
}
else
{
format = PixelFormat.Format64bppArgb;
}
}
else if(colorType == 0 && bitDepth == 16)
{
format = PixelFormat.Format16bppGrayScale;
}
else
{
if(significant == 0x00050505 && bitDepth == 8)
{
format = PixelFormat.Format16bppRgb555;
}
else if(significant == 0x00050605 && bitDepth == 8)
{
format = PixelFormat.Format16bppRgb565;
}
else if(bitDepth == 8)
{
format = PixelFormat.Format24bppRgb;
}
else
{
format = PixelFormat.Format48bppRgb;
}
}
image.Width = width;
image.Height = height;
image.PixelFormat = format;
image.LoadFormat = Image.Png;
frame = image.AddFrame(width, height, format);
}
else if(reader.Type == PLTE)
{
// We must have a frame at this point.
if(frame == null)
{
throw new FormatException
("palette specified before image header");
}
// The palette is only required for color type 3.
// Other color types use it as a hint only.
if(colorType == 3)
{
int[] palette = new int [256];
frame.Palette = palette;
Array.Clear(buffer, 0, buffer.Length);
if(reader.Length > 768)
{
reader.Read(buffer, 0, 768);
}
else
{
reader.Read(buffer, 0, buffer.Length);
}
for(index = 0; index < 256; ++index)
{
palette[index] =
Utils.ReadRGB(buffer, index * 3);
}
}
}
else if(reader.Type == tRNS)
{
// We must have a frame at this point.
if(frame == null)
{
throw new FormatException
("transparency specified before image header");
}
// We only support simple transparencies for
// color type 3 at present. The transparency
// information is ignored for other color types.
if(colorType == 3)
{
index = 0;
while(index < 256 && reader.Length > 0)
{
if(reader.Read(buffer, 0, 1) != 1)
{
break;
}
if(buffer[0] < 0x80)
{
frame.TransparentPixel = index;
break;
}
++index;
}
}
}
else if(reader.Type == sBIT)
{
// Read the number of significant bits so that
// we can detect images that started off life
// as 15-bit or 16-bit RGB.
if(reader.Length == 3)
{
reader.Read(buffer, 0, 3);
significant = Utils.ReadRGB(buffer, 0);
}
else if(reader.Length == 4)
{
reader.Read(buffer, 0, 4);
significant = Utils.ReadRGB(buffer, 0) |
(buffer[3] << 24);
}
}
else if(reader.Type == IDAT)
{
// We must have a frame at this point.
if(frame == null)
{
throw new FormatException
("image data specified before image header");
}
// There can be only one set of data chunks.
if(decompress != null)
{
throw new FormatException
("multiple image data blocks encountered");
}
// Create a zlib decompressor.
decompress = new ZlibDecompressor(reader);
// Get the pass processing function.
passFunc = GetPassFunc(colorType, bitDepth, format);
// Process the data in the image.
if(interlaceMethod == 0)
{
// No interlacing.
scanlineReader = new ScanlineReader
(decompress, width, height,
colorType, bitDepth);
passFunc(frame, scanlineReader, width, height,
0, 0, 1, 1);
}
else
{
// Use Adam7 interlacing.
for(pass = 0; pass < 7; ++pass)
{
// Calculate the width and height of the pass.
// Please refer "PNG - The Definitive Guide"
// for a totally misleading and incompatible
// description of the following code - Gopal
passWidth = width +
adam7Rules[(pass+1) * 4 + 2] - 1;
passWidth /= adam7Rules[pass * 4 + 2];
if(passWidth <= 0)
{
continue;
}
passHeight = height +
adam7Rules[(pass+1) * 4 + 3 ] - 1;
passHeight /= adam7Rules[pass * 4 + 3];
if(passHeight <= 0)
{
continue;
}
// Create a scanline reader for the pass.
scanlineReader = new ScanlineReader
(decompress, passWidth, passHeight,
colorType, bitDepth);
// Process the Adam7 pass.
passFunc(frame, scanlineReader,
passWidth, passHeight,
adam7Rules[pass * 4],
adam7Rules[pass * 4 + 1],
adam7Rules[pass * 4 + 2],
adam7Rules[pass * 4 + 3]);
}
}
// Eat any remaining IDAT data blocks.
decompress.EatRemaining();
// Skip the "Reset", because we've already done it.
continue;
}
// Reset the chunk reader and move on to the next chunk.
reader.Reset(buffer);
}
// Skip the contents of the IEND chunk and check its CRC.
reader.Skip(buffer);
// If we don't have a frame or decompressor,
// then the PNG stream was empty.
if(frame == null || decompress == null)
{
throw new FormatException("PNG did not contain an image");
}
}
// Constructor.
public ScanlineReader(ZlibDecompressor decompressor,
int width, int height,
int colorType, int bitDepth)
{
// Determine the number of bytes per pixel (rounded up),
// and the number of bytes per scan line.
switch(colorType)
{
case 0:
{
switch(bitDepth)
{
case 1:
{
bytesPerPixel = 1;
bytesPerLine = (width + 7) / 8;
}
break;
case 2:
{
bytesPerPixel = 1;
bytesPerLine = (width + 3) / 4;
}
break;
case 4:
{
bytesPerPixel = 1;
bytesPerLine = (width + 1) / 2;
}
break;
case 8:
{
bytesPerPixel = 1;
bytesPerLine = width;
}
break;
case 16:
{
bytesPerPixel = 2;
bytesPerLine = width * 2;
}
break;
}
}
break;
case 2:
{
if(bitDepth == 8)
{
bytesPerPixel = 3;
bytesPerLine = width * 3;
}
else
{
bytesPerPixel = 6;
bytesPerLine = width * 6;
}
}
break;
case 3:
{
bytesPerPixel = 1;
bytesPerLine = width;
}
break;
case 4:
{
if(bitDepth == 8)
{
bytesPerPixel = 2;
bytesPerLine = width * 2;
}
else
{
bytesPerPixel = 4;
bytesPerLine = width * 4;
}
}
break;
case 6:
{
if(bitDepth == 8)
{
bytesPerPixel = 4;
bytesPerLine = width * 4;
}
else
{
bytesPerPixel = 8;
bytesPerLine = width * 8;
}
}
break;
}
// Allocate the scanline buffers.
scanline = new byte [bytesPerLine];
prevScanline = new byte [bytesPerLine];
// Initialize the other values.
this.decompressor = decompressor;
this.y = 0;
this.height = height;
}
