int LibRaw::subtract_black_internal()
{
  CHECK_ORDER_LOW(LIBRAW_PROGRESS_RAW2_IMAGE);

  try {
    if(!is_phaseone_compressed() && (C.cblack[0] || C.cblack[1] || C.cblack[2] || C.cblack[3] || (C.cblack[4] && C.cblack[5]) ))
      {
#define BAYERC(row,col,c) imgdata.image[((row) >> IO.shrink)*S.iwidth + ((col) >> IO.shrink)][c] 
        int cblk[4],i;
        for(i=0;i<4;i++)
          cblk[i] = C.cblack[i];

        int size = S.iheight * S.iwidth;
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#define LIM(x,min,max) MAX(min,MIN(x,max))
#define CLIP(x) LIM(x,0,65535)
        int dmax = 0;
        if(C.cblack[4] && C.cblack[5])
          {
            for(i=0; i< size*4; i++)
              {
                int val = imgdata.image[0][i];
                val -= C.cblack[6 + i/4 / S.iwidth % C.cblack[4] * C.cblack[5] +
			i/4 % S.iwidth % C.cblack[5]];
                val -= cblk[i & 3];
                imgdata.image[0][i] = CLIP(val);
                if(dmax < val) dmax = val;
              }
          }
        else
          {
            for(i=0; i< size*4; i++)
              {
                int val = imgdata.image[0][i];
                val -= cblk[i & 3];
                imgdata.image[0][i] = CLIP(val);
                if(dmax < val) dmax = val;
              }
          }
        C.data_maximum = dmax & 0xffff;
#undef MIN
#undef MAX
#undef LIM
#undef CLIP
        C.maximum -= C.black;
        ZERO(C.cblack); // Yeah, we used cblack[6+] values too!
        C.black = 0;
#undef BAYERC
      }
    else
      {
        // Nothing to Do, maximum is already calculated, black level is 0, so no change
        // only calculate channel maximum;
        int idx;
        ushort *p = (ushort*)imgdata.image;
        int dmax = 0;
        for(idx=0;idx<S.iheight*S.iwidth*4;idx++)
          if(dmax < p[idx]) dmax = p[idx];
        C.data_maximum = dmax;
      }
    return 0;
  }
  catch ( LibRaw_exceptions err) {
    EXCEPTION_HANDLER(err);
  }

}
Unknown