SD3: update default training timestep / loss weighting distribution to logit_normal (#8592)

Co-authored-by: bghira <bghira@users.github.com>
Co-authored-by: Kashif Rasul <kashif.rasul@gmail.com>

examples/dreambooth/train_dreambooth_lora_sd3.py

@@ -473,7 +473,7 @@ def parse_args(input_args=None):
         ),
     )
     parser.add_argument(
-        "--weighting_scheme", type=str, default="sigma_sqrt", choices=["sigma_sqrt", "logit_normal", "mode"]
+        "--weighting_scheme", type=str, default="logit_normal", choices=["sigma_sqrt", "logit_normal", "mode"]
     )
     parser.add_argument("--logit_mean", type=float, default=0.0)
     parser.add_argument("--logit_std", type=float, default=1.0)

examples/dreambooth/train_dreambooth_sd3.py

@@ -471,7 +471,7 @@ def parse_args(input_args=None):
         ),
     )
     parser.add_argument(
-        "--weighting_scheme", type=str, default="sigma_sqrt", choices=["sigma_sqrt", "logit_normal", "mode"]
+        "--weighting_scheme", type=str, default="logit_normal", choices=["sigma_sqrt", "logit_normal", "mode"]
     )
     parser.add_argument("--logit_mean", type=float, default=0.0)
     parser.add_argument("--logit_std", type=float, default=1.0)