Modular PAG Guider

src/diffusers/__init__.py

@@ -138,6 +138,7 @@
             "AutoGuidance",
             "ClassifierFreeGuidance",
             "ClassifierFreeZeroStarGuidance",
+            "PerturbedAttentionGuidance",
             "SkipLayerGuidance",
             "SmoothedEnergyGuidance",
             "TangentialClassifierFreeGuidance",
@@ -785,6 +786,7 @@
             AutoGuidance,
             ClassifierFreeGuidance,
             ClassifierFreeZeroStarGuidance,
+            PerturbedAttentionGuidance,
             SkipLayerGuidance,
             SmoothedEnergyGuidance,
             TangentialClassifierFreeGuidance,

src/diffusers/guiders/__init__.py

@@ -22,6 +22,7 @@
     from .auto_guidance import AutoGuidance
     from .classifier_free_guidance import ClassifierFreeGuidance
     from .classifier_free_zero_star_guidance import ClassifierFreeZeroStarGuidance
+    from .perturbed_attention_guidance import PerturbedAttentionGuidance
     from .skip_layer_guidance import SkipLayerGuidance
     from .smoothed_energy_guidance import SmoothedEnergyGuidance
     from .tangential_classifier_free_guidance import TangentialClassifierFreeGuidance
@@ -31,6 +32,7 @@
         AutoGuidance,
         ClassifierFreeGuidance,
         ClassifierFreeZeroStarGuidance,
+        PerturbedAttentionGuidance,
         SkipLayerGuidance,
         SmoothedEnergyGuidance,
         TangentialClassifierFreeGuidance,

src/diffusers/guiders/perturbed_attention_guidance.py

@@ -0,0 +1,114 @@
+# Copyright 2025 The HuggingFace Team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import List, Optional, Union
+
+from ..hooks import LayerSkipConfig
+from .skip_layer_guidance import SkipLayerGuidance
+
+
+class PerturbedAttentionGuidance(SkipLayerGuidance):
+    """
+    Perturbed Attention Guidance (PAG): https://huggingface.co/papers/2403.17377
+
+    The intution behind PAG can be thought of as moving the CFG predicted distribution estimates further away from
+    worse versions of the conditional distribution estimates. PAG was one of the first techniques to introduce the idea
+    of using a worse version of the trained model for better guiding itself in the denoising process. It perturbs the
+    attention scores of the latent stream by replacing the score matrix with an identity matrix for selectively chosen
+    layers.
+
+    Additional reading:
+    - [Guiding a Diffusion Model with a Bad Version of Itself](https://huggingface.co/papers/2406.02507)
+
+    PAG is implemented as a specialization of the SkipLayerGuidance due to similarities in the configuration parameters
+    and implementation details.
+
+    Args:
+        guidance_scale (`float`, defaults to `7.5`):
+            The scale parameter for classifier-free guidance. Higher values result in stronger conditioning on the text
+            prompt, while lower values allow for more freedom in generation. Higher values may lead to saturation and
+            deterioration of image quality.
+        perturbed_guidance_scale (`float`, defaults to `2.8`):
+            The scale parameter for perturbed attention guidance.
+        perturbed_guidance_start (`float`, defaults to `0.01`):
+            The fraction of the total number of denoising steps after which perturbed attention guidance starts.
+        perturbed_guidance_stop (`float`, defaults to `0.2`):
+            The fraction of the total number of denoising steps after which perturbed attention guidance stops.
+        perturbed_guidance_layers (`int` or `List[int]`, *optional*):
+            The layer indices to apply perturbed attention guidance to. Can be a single integer or a list of integers.
+            If not provided, `skip_layer_config` must be provided.
+        skip_layer_config (`LayerSkipConfig` or `List[LayerSkipConfig]`, *optional*):
+            The configuration for the perturbed attention guidance. Can be a single `LayerSkipConfig` or a list of
+            `LayerSkipConfig`. If not provided, `perturbed_guidance_layers` must be provided.
+        guidance_rescale (`float`, defaults to `0.0`):
+            The rescale factor applied to the noise predictions. This is used to improve image quality and fix
+            overexposure. Based on Section 3.4 from [Common Diffusion Noise Schedules and Sample Steps are
+            Flawed](https://huggingface.co/papers/2305.08891).
+        use_original_formulation (`bool`, defaults to `False`):
+            Whether to use the original formulation of classifier-free guidance as proposed in the paper. By default,
+            we use the diffusers-native implementation that has been in the codebase for a long time. See
+            [~guiders.classifier_free_guidance.ClassifierFreeGuidance] for more details.
+        start (`float`, defaults to `0.01`):
+            The fraction of the total number of denoising steps after which guidance starts.
+        stop (`float`, defaults to `0.2`):
+            The fraction of the total number of denoising steps after which guidance stops.
+    """
+
+    # NOTE: The current implementation does not account for joint latent conditioning (text + image/video tokens in
+    # the same latent stream). It assumes the entire latent is a single stream of visual tokens. It would be very
+    # complex to support joint latent conditioning in a model-agnostic manner without specializing the implementation
+    # for each model architecture.
+
+    def __init__(
+        self,
+        guidance_scale: float = 7.5,
+        perturbed_guidance_scale: float = 2.8,
+        perturbed_guidance_start: float = 0.01,
+        perturbed_guidance_stop: float = 0.2,
+        perturbed_guidance_layers: Optional[Union[int, List[int]]] = None,
+        skip_layer_config: Union[LayerSkipConfig, List[LayerSkipConfig]] = None,
+        guidance_rescale: float = 0.0,
+        use_original_formulation: bool = False,
+        start: float = 0.0,
+        stop: float = 1.0,
+    ):
+        if skip_layer_config is None:
+            if perturbed_guidance_layers is None:
+                raise ValueError(
+                    "`perturbed_guidance_layers` must be provided if `skip_layer_config` is not specified."
+                )
+            skip_layer_config = LayerSkipConfig(
+                indices=perturbed_guidance_layers,
+                skip_attention=False,
+                skip_attention_scores=True,
+                skip_ff=False,
+            )
+        else:
+            if perturbed_guidance_layers is not None:
+                raise ValueError(
+                    "`perturbed_guidance_layers` should not be provided if `skip_layer_config` is specified."
+                )
+
+        super().__init__(
+            guidance_scale=guidance_scale,
+            skip_layer_guidance_scale=perturbed_guidance_scale,
+            skip_layer_guidance_start=perturbed_guidance_start,
+            skip_layer_guidance_stop=perturbed_guidance_stop,
+            skip_layer_guidance_layers=perturbed_guidance_layers,
+            skip_layer_config=skip_layer_config,
+            guidance_rescale=guidance_rescale,
+            use_original_formulation=use_original_formulation,
+            start=start,
+            stop=stop,
+        )