如何创建一个单色bitmap

 int[] pix = new int[picw * pich];
               
        for (int y = 0; y < pich; y++)
              for (int x = 0; x < picw; x++)
                  {
                  int index = y * picw + x;
                  int r = ((pix[index] >> 16) & 0xff)|0xff;
                  int g = ((pix[index] >> 8) & 0xff)|0xff;
                  int b =( pix[index] & 0xff)|0xff;
                  pix[index] = 0xff000000 | (r << 16) | (g << 8) | b;
                  
                  }
        bm1.setPixels(pix, 0, picw, 0, 0, picw, pich);
        BitmapDrawable bmp11=new BitmapDrawable(bm1);