Convert 24-bit bmp to 16-bit?

Question

I know that the .NET Framework comes with an image conversion class (the System.Drawing.Image.Save method).

But I need to convert a 24-bit (R8G8B8) bitmap image to a

Answer 1

A really straightforward way to do this is to loop over the old bitmap data and covert every pair of r8-g8-b8 values to x1-r5-g5-b5, something akin to this function:

char condense(char i)
{ 
  return (char)(i*255.0f/31.0f);
}

short transform(long input)// note that the last 8 bytes are ignored
{
  return condense(input&0xff) || (condense((input&0xff00)>>8)<<5)
    || (condense((intput&0xff0000)>>16)<<10);
}

// and somewhere in your program
{
  int len; // the length of your data in pixels
  char *data; // your data
  char *newdata; // this is where you store the new data; make sure it's allocated

  for(char *p=data; p