sclass ULetterbox1 implements IIIRecognizer<DoubleRect> {
  public void run(
    IProbabilisticScheduler scheduler,
    URecognizer.Cell cell,
    IVF1<DoubleRect> valueToAction) {
    var whole  = cell;
    var middle = cell.slice(1, 1.0/3.0, 2.0/3.0);
    
    // We assume the border is black.
    // If the picture fills the whole screen, it will tend
    // to equal brightness everywhere. Thus whole = middle*3
    // (because it's 3 times as large).
    // If only "middle" is not black, we have whole = middle.
    // Thus the border position can be estimated as:
    
    double wholePixelSum = whole.pixelSum();
    double middlePixelSum = middle.pixelSum();
    double ratio = doubleRatio(wholePixelSum, middlePixelSum);
    double borderPos = transformBetweenDoubleRanges_verbose(ratio,
      doubleRange(3, 1), doubleRange(0, 1/3.0));
    printVars(+wholePixelSum, +middlePixelSum, +ratio, +borderPos);
      
    DoubleRect rect = cell.slice(1, borderPos, 1-borderPos).rawDoubleRect();
    
    // No probabilities used.
    
    scheduler.schedule(1.0, () -> valueToAction.get(rect));

    //var antiBorder = cell.slice(1, 1.0/8.0, 1-1/8.0);
    //var border = whole.pixelSum()-antiBorder.pixelSum();
  }
}

Began life as a copy of #1032079