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| #region ----------- DLL IMPORT -----------
[DllImport("coredll.dll")]//
public static extern bool DeleteObject(IntPtr hObject);
[DllImport("coredll.dll")]
public static extern IntPtr GetDC(IntPtr hwnd);
[DllImport("coredll.dll")]//
public static extern IntPtr CreateCompatibleDC(IntPtr hdc);
[DllImport("coredll.dll")]
public static extern int ReleaseDC(IntPtr hwnd, IntPtr hdc);
[DllImport("coredll.dll")]//
public static extern int DeleteDC(IntPtr hdc);
[DllImport("coredll.dll")]//
public static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);
[DllImport("coredll.dll")]//
public static extern int BitBlt(IntPtr hdcDst, int xDst, int yDst, int w, int h, IntPtr hdcSrc, int xSrc, int ySrc, int rop);
static int SRCCOPY = 0x00CC0020;
[DllImport("coredll.dll")]//
static extern IntPtr CreateDIBSection(IntPtr hdc, ref BITMAPINFO bmi, uint Usage, out IntPtr bits, IntPtr hSection, uint dwOffset);
static uint BI_RGB = 0;
static uint DIB_RGB_COLORS = 0;
[StructLayout(LayoutKind.Sequential)]
public struct BITMAPINFO
{
public uint biSize;
public int biWidth, biHeight;
public short biPlanes, biBitCount;
public uint biCompression, biSizeImage;
public int biXPelsPerMeter, biYPelsPerMeter;
public uint biClrUsed, biClrImportant;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)]
public uint[] cols;
}
static uint MAKERGB(int r, int g, int b)
{
return ((uint)(b & 255)) | ((uint)((r & 255) << 8)) | ((uint)((g & 255) << 16));
}
#endregion
/// <summary>
/// Copies a bitmap into a 1bpp/8bpp bitmap of the same dimensions, fast
/// </summary>
/// <param name="b">original bitmap</param>
/// <param name="bpp">1 or 8, target bpp</param>
/// <returns>a 1bpp copy of the bitmap</returns>
public static Bitmap CopyToBpp(Bitmap b, int bpp)
{
if (bpp != 1 && bpp != 8) throw new ArgumentException(@"1 or 8", "bpp");
// Plan: built into Windows GDI is the ability to convert
// bitmaps from one format to another. Most of the time, this
// job is actually done by the graphics hardware accelerator card
// and so is extremely fast. The rest of the time, the job is done by
// very fast native code.
// We will call into this GDI functionality from C#. Our plan:
// (1) Convert our Bitmap into a GDI hbitmap (ie. copy unmanaged->managed)
// (2) Create a GDI monochrome hbitmap
// (3) Use GDI "BitBlt" function to copy from hbitmap into monochrome (as above)
// (4) Convert the monochrone hbitmap into a Bitmap (ie. copy unmanaged->managed)
int w = b.Width, h = b.Height;
IntPtr hbm = b.GetHbitmap(); // this is step (1)
//
// Step (2): create the monochrome bitmap.
// "BITMAPINFO" is an interop-struct which we define below.
// In GDI terms, it's a BITMAPHEADERINFO followed by an array of two RGBQUADs
BITMAPINFO bmi = new BITMAPINFO();
bmi.biSize = 40; // the size of the BITMAPHEADERINFO struct
bmi.biWidth = w;
bmi.biHeight = h;
bmi.biPlanes = 1; // "planes" are confusing. We always use just 1. Read MSDN for more info.
bmi.biBitCount = (short)bpp; // ie. 1bpp or 8bpp
bmi.biCompression = BI_RGB; // ie. the pixels in our RGBQUAD table are stored as RGBs, not palette indexes
bmi.biSizeImage = (uint)(((w + 7) & 0xFFFFFFF8) * h / 8);
bmi.biXPelsPerMeter = 1000000; // not really important
bmi.biYPelsPerMeter = 1000000; // not really important
// Now for the colour table.
uint ncols = (uint)1 << bpp; // 2 colours for 1bpp; 256 colours for 8bpp
bmi.biClrUsed = ncols;
bmi.biClrImportant = ncols;
bmi.cols = new uint[256]; // The structure always has fixed size 256, even if we end up using fewer colours
if (bpp == 1) { bmi.cols[0] = MAKERGB(0, 0, 0); bmi.cols[1] = MAKERGB(255, 255, 255); }
else { for (int i = 0; i < ncols; i++) bmi.cols[i] = MAKERGB(i, i, i); }
// For 8bpp we've created an palette with just greyscale colours.
// You can set up any palette you want here. Here are some possibilities:
// greyscale: for (int i=0; i<256; i++) bmi.cols[i]=MAKERGB(i,i,i);
// rainbow: bmi.biClrUsed=216; bmi.biClrImportant=216; int[] colv=new int[6]{0,51,102,153,204,255};
// for (int i=0; i<216; i++) bmi.cols[i]=MAKERGB(colv[i/36],colv[(i/6)%6],colv[i%6]);
// optimal: a difficult topic: http://en.wikipedia.org/wiki/Color_quantization
//
// Now create the indexed bitmap "hbm0"
IntPtr bits0; // not used for our purposes. It returns a pointer to the raw bits that make up the bitmap.
IntPtr hbm0 = CreateDIBSection(IntPtr.Zero, ref bmi, DIB_RGB_COLORS, out bits0, IntPtr.Zero, 0);
//
// Step (3): use GDI's BitBlt function to copy from original hbitmap into monocrhome bitmap
// GDI programming is kind of confusing... nb. The GDI equivalent of "Graphics" is called a "DC".
IntPtr sdc = GetDC(IntPtr.Zero); // First we obtain the DC for the screen
// Next, create a DC for the original hbitmap
IntPtr hdc = CreateCompatibleDC(sdc); SelectObject(hdc, hbm);
// and create a DC for the monochrome hbitmap
IntPtr hdc0 = CreateCompatibleDC(sdc); SelectObject(hdc0, hbm0);
// Now we can do the BitBlt:
BitBlt(hdc0, 0, 0, w, h, hdc, 0, 0, SRCCOPY);
// Step (4): convert this monochrome hbitmap back into a Bitmap:
Bitmap b0 = Image.FromHbitmap(hbm0);
//
// Finally some cleanup.
DeleteDC(hdc);
DeleteDC(hdc0);
ReleaseDC(IntPtr.Zero, sdc);
DeleteObject(hbm);
DeleteObject(hbm0);
//
return b0;
} |
