/* Input: filename of a bitmap file
* Output: byte array of the same bitmap with 1 bit per pixel
*
* Theoretically works with 8, 16, 24, or 32 bit input files;
* I've only tested with 32. Returns null on 4bpp, file itself
* if image is already 1bpp.
*
* Uncompressed DIB3 only. Returns null otherwise.
*
* May not deal well with an existing color palette.
*
* No support for endianess or negative height.
*/
public static byte[] To1bpp(string filename)
{
byte[] data = System.IO.File.ReadAllBytes(filename);
int raw_loc = BitmapConverter.GetInt(data, 0xa, 0xd);
int width = BitmapConverter.GetInt(data, 0x12, 0x15);
int height = BitmapConverter.GetInt(data, 0x16, 0x19);
int bpp = BitmapConverter.GetInt(data, 0x1c, 0x1d);
int comp = BitmapConverter.GetInt(data, 0x1e, 0x21);
// 1 bpp => done
// 4 bpp => unimplemented
if (bpp == 1)
{
return(data);
}
if (bpp == 4)
{
return(null);
}
// compression => unimplemented
if (comp != 0)
{
return(null);
}
byte[,] pixels = new byte[width, height];
int raw_size = data.Length - raw_loc;
int bytesPerRow = raw_size / height;
/* read the existing pixel values into a
* 2-dimensional array. */
int x = 0;
int y = 0;
int pix_size = bpp / 8;
int pixcount = 0;
for (int i = 0; i < raw_size; i += 0)
{
if (i > 0 && i % bytesPerRow == 0)
{
x = 0;
y++;
}
if (x < width)
{
int pixel = BitmapConverter.GetInt(data,
i + raw_loc, i + raw_loc + pix_size - 1);
i += pix_size;
pixel = pixel & 0xffffff; // no alpha
if (pixel < 0xeeeeee)
{
pixels[x, y] = 1;
}
else
{
pixels[x, y] = 0;
}
pixcount++;
}
else
{
i++; // row padding
}
x++;
}
/* create a new byte array to hold 1 bit pixels
* and add them all to it*/
int newRowBytes = (int)((width + 31) / 32.0) * 4;
byte[] newdata = new byte[newRowBytes * height];
int bits = 0;
for (int i = 0; i < newdata.Length; i++)
{
int x1 = (i % newRowBytes) * 8;
int y1 = i / newRowBytes;
int val = 0;
for (int j = 0; j < 8; j++)
{
if (x1 + j >= width) // end of pixel row, rest gets padded
{
break;
}
val = val | ((pixels[x1 + j, y1]) << (7 - j));
bits++;
}
newdata[i] = (byte)val;
}
byte[] newbmp = new byte[14 + 40 + 8 + newdata.Length];
// BMP Header
newbmp[0x0] = 0x42;
newbmp[0x1] = 0x4D;
BitmapConverter.PutInt(ref newbmp, newbmp.Length, 0x2, 0x5); // filesize
BitmapConverter.PutInt(ref newbmp, 0, 0x6, 0x9); // irrelevant
BitmapConverter.PutInt(ref newbmp, 14 + 40 + 8, 0xa, 0xd); // image data offset
// DIB Header
BitmapConverter.PutInt(ref newbmp, 40, 0xe, 0x11); // DIB3
BitmapConverter.PutInt(ref newbmp, width, 0x12, 0x15);
BitmapConverter.PutInt(ref newbmp, height, 0x16, 0x19);
BitmapConverter.PutInt(ref newbmp, 1, 0x1a, 0x1b); // planes, always 1
BitmapConverter.PutInt(ref newbmp, 1, 0x1c, 0x1d); // bpp
BitmapConverter.PutInt(ref newbmp, 0, 0x1e, 0x21); // no compression
BitmapConverter.PutInt(ref newbmp, newdata.Length, 0x22, 0x25); // image data size
int dpi = (int)(72 * 39.97 + 0.5);
BitmapConverter.PutInt(ref newbmp, dpi, 0x26, 0x29); // horizontal dpi
BitmapConverter.PutInt(ref newbmp, dpi, 0x2a, 0x2d); // vertical dpi
BitmapConverter.PutInt(ref newbmp, 2, 0x2e, 0x31); // number of colors
BitmapConverter.PutInt(ref newbmp, 0, 0x32, 0x35); // usually ignored
// Color Palette
newbmp[0x36] = 0xff; // white
newbmp[0x37] = 0xff;
newbmp[0x38] = 0xff;
newbmp[0x39] = 0x0;
newbmp[0x3a] = 0x0; // black
newbmp[0x3b] = 0x0;
newbmp[0x3c] = 0x0;
newbmp[0x3d] = 0x0;
// raw image data
Array.Copy(newdata, 0, newbmp, 0x3e, newdata.Length);
return(newbmp);
}
