code: def __generate_matrix(self, gt_image, pre_image):
      mask = (gt_image >= 0) & (gt_image < self.num_class)
      label = (
          self.num_class * gt_image[mask].astype("int")
          + pre_image[mask]
      )
      count = np.bincount(label, minlength=self.num_class**2)
      confusion_matrix = count.reshape(self.num_class, self.num_class)
      return confusion_matrix
  
imports: import os
  import time
  import tqdm
  import numpy
  from PIL import Image
  import paddle
  import paddle.nn.functional
  from paddleseg.utils import metrics, TimeAverager, calculate_eta, logger, progbar
  import datasets
  from utils import save_imgs
label_desc: Use image node_id 8 for calling the Eval obj's underlying member method code with example usage: obj.__generate_matrix(gt_image, pre_image) and returns: confusion_matrix