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();

  }

}