code: def __init__(self):
      super().__init__()
      self.conv1 = layers.ConvBNReLU(
          4, 64, kernel_size=3, padding=1, bias_attr=False
      )
      self.conv2 = layers.ConvBNReLU(
          64, 64, kernel_size=3, padding=1, bias_attr=False
      )
      self.conv3 = layers.ConvBNReLU(
          64, 64, kernel_size=3, padding=1, bias_attr=False
      )
      self.alpha_pred = layers.ConvBNReLU(
          64, 1, kernel_size=3, padding=1, bias_attr=False
      )
  
imports: from collections import defaultdict
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddleseg.models import layers
  from paddleseg import utils
  from paddleseg.cvlibs import manager
  from ppmatting.models.losses import MRSD
label_desc: Use image node_id 1 to create a new Refine object from inherited base classes: nn with example: obj = Refine()