def METHOD_NAME(self):
    self.good_tiles = []
    for im_idx in self.image_indexes:
        item = self.image_provider[im_idx]
        positions = self.cropper.cropper_positions(item.image)
        if self.image_provider.has_alpha:
            item = self.image_provider[im_idx]
            alpha_generator = self.cropper.sequential_crops(item.alpha)
            for idx, alpha in enumerate(alpha_generator):
                if np.mean(alpha) > 5:
                    self.good_tiles.append((im_idx, *positions[idx]))
        else:
            for pos in positions:
                self.good_tiles.append((im_idx, *pos))