tesseract: Page numbers not detected in various cases

I made some progress. It looks like in the example of https://archive.org/~merlijn/tesseract-pagenumbers/sim_biblical-theology-bulletin_spring-1990_20_1_0004.jpg with default segmentation - the ‘3’ is never accepted as a blob that is text. I found out that this is the case because the blob disappears after the call to TidyBlobs():

In particular, the call to block->DeleteUnownedNoise(); is what removes the 3. Commenting that call makes the ‘3’ visible in the blobs, but of course this doesn’t help since it wasn’t detected by the column finder, per the hint in that function:

// Deletes noise blobs from all lists where not owned by a ColPartition.

So somehow it is not picked up by the page segmentation. The “Image blobs” window shows this:

void TO_BLOCK::plot_noise_blobs(ScrollView *win) {
  BLOBNBOX::PlotNoiseBlobs(&noise_blobs, ScrollView::RED, ScrollView::RED, win);
  BLOBNBOX::PlotNoiseBlobs(&small_blobs, ScrollView::RED, ScrollView::RED, win);
  BLOBNBOX::PlotNoiseBlobs(&large_blobs, ScrollView::RED, ScrollView::RED, win);
  BLOBNBOX::PlotNoiseBlobs(&blobs, ScrollView::RED, ScrollView::RED, win);
}

And:

void BLOBNBOX::PlotNoiseBlobs(BLOBNBOX_LIST *list, ScrollView::Color body_colour,
                              ScrollView::Color child_colour, ScrollView *win) {
  BLOBNBOX_IT it(list);
  for (it.mark_cycle_pt(); !it.cycled_list(); it.forward()) {
    BLOBNBOX *blob = it.data();
    if (blob->DeletableNoise()) {
      blob->plot(win, body_colour, child_colour);
    }
  }
}

So red indicates it is seen as noise, indeed. Deletetable noise looks as follows:

bool DeletableNoise() const {
  return owner() == nullptr && region_type() == BRT_NOISE;
}

So this means the ‘3’ both doesn’t have an “owner” (presumably the ColPartition mentioned earlier) and also has region type noise. There are several places in the code that set the BRT_NOISE value, so going over those seems like the next logical step.