Method ProcessImage

Filters/Hybrid/vtkImageToPolyDataFilter.cxx:673–763

Marks connected regions with different colors.

// Marks connected regions with different colors.
int vtkImageToPolyDataFilter::ProcessImage(vtkUnsignedCharArray* scalars, int dims[2])
{
  int numPixels = dims[0] * dims[1];
  vtkIdList *wave, *wave2, *tmpWave;
  int numIds, regionNumber, i, j, k, id, x, y, numNeighbors;
  unsigned char *neighbors[4], *ptr;
  unsigned char* pixels = scalars->GetPointer(0);

  // Collect groups of pixels together into similar colored regions. These
  // will be eventually grouped into polygons and/or lines.
  //
  // mark all pixels unvisited
  regionNumber = -1;
  this->Visited = new int[numPixels];
  memset(this->Visited, -1, numPixels * sizeof(int));

  // set up the connected traversal
  wave = vtkIdList::New();
  wave->Allocate(static_cast<int>(numPixels / 4.0), static_cast<int>(numPixels / 4.0));
  wave2 = vtkIdList::New();
  wave2->Allocate(static_cast<int>(numPixels / 4.0), static_cast<int>(numPixels / 4.0));

  // visit connected pixels. Pixels are connected if they are topologically
  // adjacent and they have "equal" color values.
  for (i = 0; i < numPixels; i++)
  {
    if (this->Visited[i] == -1)
    { // start a connected wave
      this->Visited[i] = ++regionNumber;
      ptr = pixels + 3 * i;
      this->PolyColors->InsertValue(3 * regionNumber, ptr[0]); // assign color
      this->PolyColors->InsertValue(3 * regionNumber + 1, ptr[1]);
      this->PolyColors->InsertValue(3 * regionNumber + 2, ptr[2]);
      wave->Reset();
      wave2->Reset();

      // To prevent creating polygons with inner loops, we're going to start
      // the wave as a "vertical" stack of pixels, and then propagate the
      // wave horizontally only.
      wave->InsertId(0, i);
      this->GetIJ(i, x, y, dims);
      while ((numNeighbors = this->GetNeighbors(ptr, x, y, dims, neighbors, 1)))
      {
        id = (neighbors[0] - pixels) / 3;
        if (this->Visited[id] == -1 && this->IsSameColor(ptr, neighbors[0]))
        {
          this->Visited[id] = regionNumber;
          wave->InsertNextId(id);
          ptr = pixels + 3 * id;
          this->GetIJ(id, x, y, dims);
        }
        else
        {
          break;
        }
      }

      // Okay, defined vertical wave, now propagate horizontally