Hi, here is the answer for it..

To convert 8-bit to 24-bit image, one way is to draw another bitmap based on original bitmap's pixel color:

Bitmap image = new Bitmap(@"C:\bit8.bmp");
Bitmap bitmap = new Bitmap(image.Width, image.Height, System.Drawing.Imaging.PixelFormat.Format24bppRgb) ;
for (int i = 0; i < image.Width; i++)
{
for (int j = 0; j < image.Height; j++)
{
Color temp = image.GetPixel(i, j);
bitmap.SetPixel(i, j, temp);
}
}
bitmap.Save(@"C:\bit24.bmp", System.Drawing.Imaging.ImageFormat.Bmp);