Updates to GAN script examples (Project-MONAI#1727)

### Description
This updates the two example scripts which used old code MONAI no long
has.

### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

---------

Signed-off-by: Eric Kerfoot <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: YunLiu <[email protected]>

Author: 3 people

modules/engines/gan_evaluation.py

@@ -23,18 +23,21 @@
 import torch
 
 import monai
-from monai.data import png_writer
 from monai.engines.utils import default_make_latent as make_latent
 from monai.networks.nets import Generator
 from monai.utils.misc import set_determinism
+from monai.data.image_writer import PILWriter
 
 
 def save_generator_fakes(run_folder, g_output_tensor):
+    writer_obj = PILWriter(output_dtype=np.uint8)
+
     for i, image in enumerate(g_output_tensor):
-        filename = "gen-fake-%d.png" % i
+        filename = f"gen-fake-{i}.png"
         save_path = os.path.join(run_folder, filename)
-        img_array = image[0].cpu().data.numpy()
-        png_writer.write_png(img_array, save_path, scale=255)
+        img_array = monai.transforms.utils.rescale_array(image[0].cpu().data.numpy())
+        writer_obj.set_data_array(img_array, channel_dim=None)
+        writer_obj.write(save_path, format="PNG")
 
 
 def main():

modules/engines/gan_training.py

@@ -29,7 +29,7 @@
 import numpy as np
 import monai
 from monai.apps.utils import download_and_extract
-from monai.data import CacheDataset, DataLoader, png_writer
+from monai.data import CacheDataset, DataLoader
 from monai.engines import GanTrainer
 from monai.engines.utils import GanKeys as Keys
 from monai.engines.utils import default_make_latent as make_latent
@@ -47,6 +47,7 @@
     EnsureTypeD,
 )
 from monai.utils.misc import set_determinism
+from monai.data.image_writer import PILWriter
 
 
 def main():
@@ -193,11 +194,15 @@ def generator_loss(gen_images):
     test_img_count = 10
     test_latents = make_latent(test_img_count, latent_size).to(device)
     fakes = gen_net(test_latents)
+
+    writer_obj = PILWriter(output_dtype=np.uint8)
+
     for i, image in enumerate(fakes):
-        filename = "gen-fake-final-%d.png" % i
+        filename = f"gen-fake-final-{i}.png"
         save_path = os.path.join(run_dir, filename)
-        img_array = image[0].cpu().data.numpy()
-        png_writer.write_png(img_array, save_path, scale=255)
+        img_array = monai.transforms.utils.rescale_array(image[0].cpu().data.numpy())
+        writer_obj.set_data_array(img_array, channel_dim=None)
+        writer_obj.write(save_path, format="PNG")
 
 
 if __name__ == "__main__":