Feature: Add Mambo-G Guidance as Guider

src/diffusers/guiders/__init__.py

@@ -25,6 +25,7 @@
     from .classifier_free_zero_star_guidance import ClassifierFreeZeroStarGuidance
     from .frequency_decoupled_guidance import FrequencyDecoupledGuidance
     from .guider_utils import BaseGuidance
+    from .magnitude_aware_guidance import MagnitudeAwareGuidance
     from .perturbed_attention_guidance import PerturbedAttentionGuidance
     from .skip_layer_guidance import SkipLayerGuidance
     from .smoothed_energy_guidance import SmoothedEnergyGuidance

src/diffusers/guiders/magnitude_aware_guidance.py

@@ -0,0 +1,159 @@
+# 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.
+
+import math
+from typing import TYPE_CHECKING, Dict, List, Optional, Tuple, Union
+
+import torch
+
+from ..configuration_utils import register_to_config
+from .guider_utils import BaseGuidance, GuiderOutput, rescale_noise_cfg
+
+
+if TYPE_CHECKING:
+    from ..modular_pipelines.modular_pipeline import BlockState
+
+
+class MagnitudeAwareGuidance(BaseGuidance):
+    """
+    Magnitude-Aware Mitigation for Boosted Guidance (MAMBO-G): https://huggingface.co/papers/2508.03442
+
+    Args:
+        guidance_scale (`float`, defaults to `10.0`):
+            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.
+        alpha (`float`, defaults to `8.0`):
+            The alpha parameter for the magnitude-aware guidance. Higher values cause more aggressive supression of
+            guidance scale when the magnitude of the guidance update is large.
+        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 `0.0`):
+            The fraction of the total number of denoising steps after which guidance starts.
+        stop (`float`, defaults to `1.0`):
+            The fraction of the total number of denoising steps after which guidance stops.
+    """
+
+    _input_predictions = ["pred_cond", "pred_uncond"]
+
+    @register_to_config
+    def __init__(
+        self,
+        guidance_scale: float = 10.0,
+        alpha: float = 8.0,
+        guidance_rescale: float = 0.0,
+        use_original_formulation: bool = False,
+        start: float = 0.0,
+        stop: float = 1.0,
+        enabled: bool = True,
+    ):
+        super().__init__(start, stop, enabled)
+
+        self.guidance_scale = guidance_scale
+        self.alpha = alpha
+        self.guidance_rescale = guidance_rescale
+        self.use_original_formulation = use_original_formulation
+
+    def prepare_inputs(self, data: Dict[str, Tuple[torch.Tensor, torch.Tensor]]) -> List["BlockState"]:
+        tuple_indices = [0] if self.num_conditions == 1 else [0, 1]
+        data_batches = []
+        for tuple_idx, input_prediction in zip(tuple_indices, self._input_predictions):
+            data_batch = self._prepare_batch(data, tuple_idx, input_prediction)
+            data_batches.append(data_batch)
+        return data_batches
+
+    def prepare_inputs_from_block_state(
+        self, data: "BlockState", input_fields: Dict[str, Union[str, Tuple[str, str]]]
+    ) -> List["BlockState"]:
+        tuple_indices = [0] if self.num_conditions == 1 else [0, 1]
+        data_batches = []
+        for tuple_idx, input_prediction in zip(tuple_indices, self._input_predictions):
+            data_batch = self._prepare_batch_from_block_state(input_fields, data, tuple_idx, input_prediction)
+            data_batches.append(data_batch)
+        return data_batches
+
+    def forward(self, pred_cond: torch.Tensor, pred_uncond: Optional[torch.Tensor] = None) -> GuiderOutput:
+        pred = None
+
+        if not self._is_mambo_g_enabled():
+            pred = pred_cond
+        else:
+            pred = mambo_guidance(
+                pred_cond,
+                pred_uncond,
+                self.guidance_scale,
+                self.alpha,
+                self.use_original_formulation,
+            )
+
+        if self.guidance_rescale > 0.0:
+            pred = rescale_noise_cfg(pred, pred_cond, self.guidance_rescale)
+
+        return GuiderOutput(pred=pred, pred_cond=pred_cond, pred_uncond=pred_uncond)
+
+    @property
+    def is_conditional(self) -> bool:
+        return self._count_prepared == 1
+
+    @property
+    def num_conditions(self) -> int:
+        num_conditions = 1
+        if self._is_mambo_g_enabled():
+            num_conditions += 1
+        return num_conditions
+
+    def _is_mambo_g_enabled(self) -> bool:
+        if not self._enabled:
+            return False
+
+        is_within_range = True
+        if self._num_inference_steps is not None:
+            skip_start_step = int(self._start * self._num_inference_steps)
+            skip_stop_step = int(self._stop * self._num_inference_steps)
+            is_within_range = skip_start_step <= self._step < skip_stop_step
+
+        is_close = False
+        if self.use_original_formulation:
+            is_close = math.isclose(self.guidance_scale, 0.0)
+        else:
+            is_close = math.isclose(self.guidance_scale, 1.0)
+
+        return is_within_range and not is_close
+
+
+def mambo_guidance(
+    pred_cond: torch.Tensor,
+    pred_uncond: torch.Tensor,
+    guidance_scale: float,
+    alpha: float = 8.0,
+    use_original_formulation: bool = False,
+):
+    dim = list(range(1, len(pred_cond.shape)))
+    diff = pred_cond - pred_uncond
+    ratio = torch.norm(diff, dim=dim, keepdim=True) / torch.norm(pred_uncond, dim=dim, keepdim=True)
+    guidance_scale_final = (
+        guidance_scale * torch.exp(-alpha * ratio)
+        if use_original_formulation
+        else 1.0 + (guidance_scale - 1.0) * torch.exp(-alpha * ratio)
+    )
+    pred = pred_cond if use_original_formulation else pred_uncond
+    pred = pred + guidance_scale_final * diff
+
+    return pred