walltime (time.time()) seconds after epoch of event
     * **dataformats** (*str*) -- Image data format specification
       of the form CHW, HWC, HW, WH, etc.

  Shape:
     img_tensor: Default is (3, H, W). You can use
     "torchvision.utils.make_grid()" to convert a batch of tensor
     into 3xHxW format or call "add_images" and let us do the job.
     Tensor with (1, H, W), (H, W), (H, W, 3) is also suitable as
     long as corresponding "dataformats" argument is passed, e.g.
     "CHW", "HWC", "HW".

  Examples:

     from torch.utils.tensorboard import SummaryWriter
     import numpy as np
     img = np.zeros((3, 100, 100))
     img[0] = np.arange(0, 10000).reshape(100, 100) / 10000
     img[1] = 1 - np.arange(0, 10000).reshape(100, 100) / 10000

     img_HWC = np.zeros((100, 100, 3))
     img_HWC[:, :, 0] = np.arange(0, 10000).reshape(100, 100) / 10000
