feat: Add Epsilon Scaling node for exposure bias correction (comfyanonymous#10132)

Author: Koratahiu

comfy_extras/nodes_eps.py

@@ -0,0 +1,60 @@
+class EpsilonScaling:
+    """
+    Implements the Epsilon Scaling method from 'Elucidating the Exposure Bias in Diffusion Models'
+    (https://arxiv.org/abs/2308.15321v6).
+
+    This method mitigates exposure bias by scaling the predicted noise during sampling,
+    which can significantly improve sample quality. This implementation uses the "uniform schedule"
+    recommended by the paper for its practicality and effectiveness.
+    """
+    @classmethod
+    def INPUT_TYPES(s):
+        return {
+            "required": {
+                "model": ("MODEL",),
+                "scaling_factor": ("FLOAT", {
+                    "default": 1.005,
+                    "min": 0.5,
+                    "max": 1.5,
+                    "step": 0.001,
+                    "display": "number"
+                }),
+            }
+        }
+
+    RETURN_TYPES = ("MODEL",)
+    FUNCTION = "patch"
+
+    CATEGORY = "model_patches/unet"
+
+    def patch(self, model, scaling_factor):
+        # Prevent division by zero, though the UI's min value should prevent this.
+        if scaling_factor == 0:
+            scaling_factor = 1e-9
+
+        def epsilon_scaling_function(args):
+            """
+            This function is applied after the CFG guidance has been calculated.
+            It recalculates the denoised latent by scaling the predicted noise.
+            """
+            denoised = args["denoised"]
+            x = args["input"]
+
+            noise_pred = x - denoised
+
+            scaled_noise_pred = noise_pred / scaling_factor
+
+            new_denoised = x - scaled_noise_pred
+
+            return new_denoised
+
+        # Clone the model patcher to avoid modifying the original model in place
+        model_clone = model.clone()
+
+        model_clone.set_model_sampler_post_cfg_function(epsilon_scaling_function)
+
+        return (model_clone,)
+
+NODE_CLASS_MAPPINGS = {
+    "Epsilon Scaling": EpsilonScaling
+}

nodes.py

@@ -2297,6 +2297,7 @@ async def init_builtin_extra_nodes():
         "nodes_gits.py",
         "nodes_controlnet.py",
         "nodes_hunyuan.py",
+        "nodes_eps.py",
         "nodes_flux.py",
         "nodes_lora_extract.py",
         "nodes_torch_compile.py",