class_docstr: Convert an image from RGB to RGBA.
  
  Add an alpha channel to existing RGB image.
  
  Args:
      alpha_val: A float number for the alpha value or a tensor
        of shape :math:`(*,1,H,W)`.
  
  Returns:
      torch.Tensor: RGBA version of the image with shape :math:`(*,4,H,W)`.
  
  Shape:
      - image: :math:`(*, 3, H, W)`
      - output: :math:`(*, 4, H, W)`
  
  .. note:: The current functionality is NOT supported by Torchscript.
  
  Example:
      >>> input = torch.rand(2, 3, 4, 5)
      >>> rgba = RgbToRgba(1.)
      >>> output = rgba(input)  # 2x4x4x5
code: def forward(self, image: torch.Tensor) -> torch.Tensor:
      return rgb_to_rgba(image, self.alpha_val)
  
imports: from typing import Union, cast
  import torch
  from torch import nn
label_desc: Use image node_id 2 for calling the RgbToRgba obj's underlying member method code with example usage: obj.forward(image) and returns: rgb_to_rgba