How can i define a 8 bit grayscale image directly ?

Question

The following code is used to create a 8 bit bitmap

Bitmap b = new Bitmap(columns, rows, PixelFormat.Format8bppIndexed);
BitmapData bmd = b.LockBits(new Rectangle(0, 0, columns, rows), ImageLockMode.ReadWrite, b.PixelFormat);

But when i save it it is saved as a 8 bit color bitmap. Is it possible to directly create a 8 bit grayscale bitmap without creating a 8 bit color bitmap and later having to convert it to a grayscale ?

Answer 1

I just met this problem and solved it, with the help of this.

But I will put my quick solution here, hope it helps you.
BITMAP files contain four parts, one is the palette, which decides how the colors should be displayed. So here we modify the palette of our Bitmap file:

myBMP = new Bitmap(_xSize, _ySize, _xSize, System.Drawing.Imaging.PixelFormat.Format8bppIndexed, _pImage);
//_pImage is the pointer for our image
//Change palatte of 8bit indexed BITMAP. Make r(i)=g(i)=b(i)
ColorPalette _palette = myBMP.Palette;
Color[] _entries = _palette.Entries;
for (int i = 0; i < 256; i++)
{
    Color b = new Color();
    b = Color.FromArgb((byte)i, (byte)i, (byte)i);
    _entries[i] = b;
}
myBMP.Palette = _palette;
return myBMP;