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# 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 flax
import flax.linen as nn
import jax
import jax.numpy as jnp
from flax.core.frozen_dict import FrozenDict
from ...configuration_utils import ConfigMixin, flax_register_to_config
from ...utils import BaseOutput, logging
from ..embeddings_flax import FlaxTimestepEmbedding, FlaxTimesteps
from ..modeling_flax_utils import FlaxModelMixin
from .unet_2d_blocks_flax import (
FlaxCrossAttnDownBlock2D,
FlaxCrossAttnUpBlock2D,
FlaxDownBlock2D,
FlaxUNetMidBlock2DCrossAttn,
FlaxUpBlock2D,
)
logger = logging.get_logger(__name__)
@flax.struct.dataclass
class FlaxUNet2DConditionOutput(BaseOutput):
"""
The output of [`FlaxUNet2DConditionModel`].
Args:
sample (`jnp.ndarray` of shape `(batch_size, num_channels, height, width)`):
The hidden states output conditioned on `encoder_hidden_states` input. Output of last layer of model.
"""
sample: jnp.ndarray
@flax_register_to_config
class FlaxUNet2DConditionModel(nn.Module, FlaxModelMixin, ConfigMixin):
r"""
A conditional 2D UNet model that takes a noisy sample, conditional state, and a timestep and returns a sample
shaped output.
This model inherits from [`FlaxModelMixin`]. Check the superclass documentation for it's generic methods
implemented for all models (such as downloading or saving).
This model is also a Flax Linen [flax.linen.Module](https://flax.readthedocs.io/en/latest/flax.linen.html#module)
subclass. Use it as a regular Flax Linen module and refer to the Flax documentation for all matters related to its
general usage and behavior.
Inherent JAX features such as the following are supported:
- [Just-In-Time (JIT) compilation](https://jax.readthedocs.io/en/latest/jax.html#just-in-time-compilation-jit)
- [Automatic Differentiation](https://jax.readthedocs.io/en/latest/jax.html#automatic-differentiation)
- [Vectorization](https://jax.readthedocs.io/en/latest/jax.html#vectorization-vmap)
- [Parallelization](https://jax.readthedocs.io/en/latest/jax.html#parallelization-pmap)
Parameters:
sample_size (`int`, *optional*):
The size of the input sample.
in_channels (`int`, *optional*, defaults to 4):
The number of channels in the input sample.
out_channels (`int`, *optional*, defaults to 4):
The number of channels in the output.
down_block_types (`tuple[str]`, *optional*, defaults to `("FlaxCrossAttnDownBlock2D", "FlaxCrossAttnDownBlock2D", "FlaxCrossAttnDownBlock2D", "FlaxDownBlock2D")`):
The tuple of downsample blocks to use.
up_block_types (`tuple[str]`, *optional*, defaults to `("FlaxUpBlock2D", "FlaxCrossAttnUpBlock2D", "FlaxCrossAttnUpBlock2D", "FlaxCrossAttnUpBlock2D")`):
The tuple of upsample blocks to use.
mid_block_type (`str`, *optional*, defaults to `"UNetMidBlock2DCrossAttn"`):
Block type for middle of UNet, it can be one of `UNetMidBlock2DCrossAttn`. If `None`, the mid block layer
is skipped.
block_out_channels (`tuple[int]`, *optional*, defaults to `(320, 640, 1280, 1280)`):
The tuple of output channels for each block.
layers_per_block (`int`, *optional*, defaults to 2):
The number of layers per block.
attention_head_dim (`int` or `tuple[int]`, *optional*, defaults to 8):
The dimension of the attention heads.
num_attention_heads (`int` or `tuple[int]`, *optional*):
The number of attention heads.
cross_attention_dim (`int`, *optional*, defaults to 768):
The dimension of the cross attention features.
dropout (`float`, *optional*, defaults to 0):
Dropout probability for down, up and bottleneck blocks.
flip_sin_to_cos (`bool`, *optional*, defaults to `True`):
Whether to flip the sin to cos in the time embedding.
freq_shift (`int`, *optional*, defaults to 0): The frequency shift to apply to the time embedding.
use_memory_efficient_attention (`bool`, *optional*, defaults to `False`):
Enable memory efficient attention as described [here](https://huggingface.co/papers/2112.05682).
split_head_dim (`bool`, *optional*, defaults to `False`):
Whether to split the head dimension into a new axis for the self-attention computation. In most cases,
enabling this flag should speed up the computation for Stable Diffusion 2.x and Stable Diffusion XL.
"""
sample_size: int = 32
in_channels: int = 4
out_channels: int = 4
down_block_types: tuple[str, ...] = (
"CrossAttnDownBlock2D",
"CrossAttnDownBlock2D",
"CrossAttnDownBlock2D",
"DownBlock2D",
)
up_block_types: tuple[str, ...] = ("UpBlock2D", "CrossAttnUpBlock2D", "CrossAttnUpBlock2D", "CrossAttnUpBlock2D")
mid_block_type: str | None = "UNetMidBlock2DCrossAttn"
only_cross_attention: bool | tuple[bool] = False
block_out_channels: tuple[int, ...] = (320, 640, 1280, 1280)
layers_per_block: int = 2
attention_head_dim: int | tuple[int, ...] = 8
num_attention_heads: int | tuple[int, ...] | None = None
cross_attention_dim: int = 1280
dropout: float = 0.0
use_linear_projection: bool = False
dtype: jnp.dtype = jnp.float32
flip_sin_to_cos: bool = True
freq_shift: int = 0
use_memory_efficient_attention: bool = False
split_head_dim: bool = False
transformer_layers_per_block: int | tuple[int, ...] = 1
addition_embed_type: str | None = None
addition_time_embed_dim: int | None = None
addition_embed_type_num_heads: int = 64
projection_class_embeddings_input_dim: int | None = None
def init_weights(self, rng: jax.Array) -> FrozenDict:
# init input tensors
sample_shape = (1, self.in_channels, self.sample_size, self.sample_size)
sample = jnp.zeros(sample_shape, dtype=jnp.float32)
timesteps = jnp.ones((1,), dtype=jnp.int32)
encoder_hidden_states = jnp.zeros((1, 1, self.cross_attention_dim), dtype=jnp.float32)
params_rng, dropout_rng = jax.random.split(rng)
rngs = {"params": params_rng, "dropout": dropout_rng}
added_cond_kwargs = None
if self.addition_embed_type == "text_time":
# we retrieve the expected `text_embeds_dim` by first checking if the architecture is a refiner
# or non-refiner architecture and then by "reverse-computing" from `projection_class_embeddings_input_dim`
is_refiner = (
5 * self.config.addition_time_embed_dim + self.config.cross_attention_dim
== self.config.projection_class_embeddings_input_dim
)
num_micro_conditions = 5 if is_refiner else 6
text_embeds_dim = self.config.projection_class_embeddings_input_dim - (
num_micro_conditions * self.config.addition_time_embed_dim
)
time_ids_channels = self.projection_class_embeddings_input_dim - text_embeds_dim
time_ids_dims = time_ids_channels // self.addition_time_embed_dim
added_cond_kwargs = {
"text_embeds": jnp.zeros((1, text_embeds_dim), dtype=jnp.float32),
"time_ids": jnp.zeros((1, time_ids_dims), dtype=jnp.float32),
}
return self.init(rngs, sample, timesteps, encoder_hidden_states, added_cond_kwargs)["params"]
def setup(self) -> None:
logger.warning(
"Flax classes are deprecated and will be removed in Diffusers v1.0.0. We "
"recommend migrating to PyTorch classes or pinning your version of Diffusers."
)
block_out_channels = self.block_out_channels
time_embed_dim = block_out_channels[0] * 4
if self.num_attention_heads is not None:
raise ValueError(
"At the moment it is not possible to define the number of attention heads via `num_attention_heads` because of a naming issue as described in https://github.com/huggingface/diffusers/issues/2011#issuecomment-1547958131. Passing `num_attention_heads` will only be supported in diffusers v0.19."
)
# If `num_attention_heads` is not defined (which is the case for most models)
# it will default to `attention_head_dim`. This looks weird upon first reading it and it is.
# The reason for this behavior is to correct for incorrectly named variables that were introduced
# when this library was created. The incorrect naming was only discovered much later in https://github.com/huggingface/diffusers/issues/2011#issuecomment-1547958131
# Changing `attention_head_dim` to `num_attention_heads` for 40,000+ configurations is too backwards breaking
# which is why we correct for the naming here.
num_attention_heads = self.num_attention_heads or self.attention_head_dim
# input
self.conv_in = nn.Conv(
block_out_channels[0],
kernel_size=(3, 3),
strides=(1, 1),
padding=((1, 1), (1, 1)),
dtype=self.dtype,
)
# time
self.time_proj = FlaxTimesteps(
block_out_channels[0], flip_sin_to_cos=self.flip_sin_to_cos, freq_shift=self.config.freq_shift
)
self.time_embedding = FlaxTimestepEmbedding(time_embed_dim, dtype=self.dtype)
only_cross_attention = self.only_cross_attention
if isinstance(only_cross_attention, bool):
only_cross_attention = (only_cross_attention,) * len(self.down_block_types)
if isinstance(num_attention_heads, int):
num_attention_heads = (num_attention_heads,) * len(self.down_block_types)
# transformer layers per block
transformer_layers_per_block = self.transformer_layers_per_block
if isinstance(transformer_layers_per_block, int):
transformer_layers_per_block = [transformer_layers_per_block] * len(self.down_block_types)
# addition embed types
if self.addition_embed_type is None:
self.add_embedding = None
elif self.addition_embed_type == "text_time":
if self.addition_time_embed_dim is None:
raise ValueError(
f"addition_embed_type {self.addition_embed_type} requires `addition_time_embed_dim` to not be None"
)
self.add_time_proj = FlaxTimesteps(self.addition_time_embed_dim, self.flip_sin_to_cos, self.freq_shift)
self.add_embedding = FlaxTimestepEmbedding(time_embed_dim, dtype=self.dtype)
else:
raise ValueError(f"addition_embed_type: {self.addition_embed_type} must be None or `text_time`.")
# down
down_blocks = []
output_channel = block_out_channels[0]
for i, down_block_type in enumerate(self.down_block_types):
input_channel = output_channel
output_channel = block_out_channels[i]
is_final_block = i == len(block_out_channels) - 1
if down_block_type == "CrossAttnDownBlock2D":
down_block = FlaxCrossAttnDownBlock2D(
in_channels=input_channel,
out_channels=output_channel,
dropout=self.dropout,
num_layers=self.layers_per_block,
transformer_layers_per_block=transformer_layers_per_block[i],
num_attention_heads=num_attention_heads[i],
add_downsample=not is_final_block,
use_linear_projection=self.use_linear_projection,
only_cross_attention=only_cross_attention[i],
use_memory_efficient_attention=self.use_memory_efficient_attention,
split_head_dim=self.split_head_dim,
dtype=self.dtype,
)
else:
down_block = FlaxDownBlock2D(
in_channels=input_channel,
out_channels=output_channel,
dropout=self.dropout,
num_layers=self.layers_per_block,
add_downsample=not is_final_block,
dtype=self.dtype,
)
down_blocks.append(down_block)
self.down_blocks = down_blocks
# mid
if self.config.mid_block_type == "UNetMidBlock2DCrossAttn":
self.mid_block = FlaxUNetMidBlock2DCrossAttn(
in_channels=block_out_channels[-1],
dropout=self.dropout,
num_attention_heads=num_attention_heads[-1],
transformer_layers_per_block=transformer_layers_per_block[-1],
use_linear_projection=self.use_linear_projection,
use_memory_efficient_attention=self.use_memory_efficient_attention,
split_head_dim=self.split_head_dim,
dtype=self.dtype,
)
elif self.config.mid_block_type is None:
self.mid_block = None
else:
raise ValueError(f"Unexpected mid_block_type {self.config.mid_block_type}")
# up
up_blocks = []
reversed_block_out_channels = list(reversed(block_out_channels))
reversed_num_attention_heads = list(reversed(num_attention_heads))
only_cross_attention = list(reversed(only_cross_attention))
output_channel = reversed_block_out_channels[0]
reversed_transformer_layers_per_block = list(reversed(transformer_layers_per_block))
for i, up_block_type in enumerate(self.up_block_types):
prev_output_channel = output_channel
output_channel = reversed_block_out_channels[i]
input_channel = reversed_block_out_channels[min(i + 1, len(block_out_channels) - 1)]
is_final_block = i == len(block_out_channels) - 1
if up_block_type == "CrossAttnUpBlock2D":
up_block = FlaxCrossAttnUpBlock2D(
in_channels=input_channel,
out_channels=output_channel,
prev_output_channel=prev_output_channel,
num_layers=self.layers_per_block + 1,
transformer_layers_per_block=reversed_transformer_layers_per_block[i],
num_attention_heads=reversed_num_attention_heads[i],
add_upsample=not is_final_block,
dropout=self.dropout,
use_linear_projection=self.use_linear_projection,
only_cross_attention=only_cross_attention[i],
use_memory_efficient_attention=self.use_memory_efficient_attention,
split_head_dim=self.split_head_dim,
dtype=self.dtype,
)
else:
up_block = FlaxUpBlock2D(
in_channels=input_channel,
out_channels=output_channel,
prev_output_channel=prev_output_channel,
num_layers=self.layers_per_block + 1,
add_upsample=not is_final_block,
dropout=self.dropout,
dtype=self.dtype,
)
up_blocks.append(up_block)
prev_output_channel = output_channel
self.up_blocks = up_blocks
# out
self.conv_norm_out = nn.GroupNorm(num_groups=32, epsilon=1e-5)
self.conv_out = nn.Conv(
self.out_channels,
kernel_size=(3, 3),
strides=(1, 1),
padding=((1, 1), (1, 1)),
dtype=self.dtype,
)
def __call__(
self,
sample: jnp.ndarray,
timesteps: jnp.ndarray | float | int,
encoder_hidden_states: jnp.ndarray,
added_cond_kwargs: dict | FrozenDict | None = None,
down_block_additional_residuals: tuple[jnp.ndarray, ...] | None = None,
mid_block_additional_residual: jnp.ndarray | None = None,
return_dict: bool = True,
train: bool = False,
) -> FlaxUNet2DConditionOutput | tuple[jnp.ndarray]:
r"""
Args:
sample (`jnp.ndarray`): (batch, channel, height, width) noisy inputs tensor
timestep (`jnp.ndarray` or `float` or `int`): timesteps
encoder_hidden_states (`jnp.ndarray`): (batch_size, sequence_length, hidden_size) encoder hidden states
added_cond_kwargs: (`dict`, *optional*):
A kwargs dictionary containing additional embeddings that if specified are added to the embeddings that
are passed along to the UNet blocks.
down_block_additional_residuals: (`tuple` of `torch.Tensor`, *optional*):
A tuple of tensors that if specified are added to the residuals of down unet blocks.
mid_block_additional_residual: (`torch.Tensor`, *optional*):
A tensor that if specified is added to the residual of the middle unet block.
return_dict (`bool`, *optional*, defaults to `True`):
Whether or not to return a [`models.unets.unet_2d_condition_flax.FlaxUNet2DConditionOutput`] instead of
a plain tuple.
train (`bool`, *optional*, defaults to `False`):
Use deterministic functions and disable dropout when not training.
Returns:
[`~models.unets.unet_2d_condition_flax.FlaxUNet2DConditionOutput`] or `tuple`:
[`~models.unets.unet_2d_condition_flax.FlaxUNet2DConditionOutput`] if `return_dict` is True, otherwise a
`tuple`. When returning a tuple, the first element is the sample tensor.
"""
# 1. time
if not isinstance(timesteps, jnp.ndarray):
timesteps = jnp.array([timesteps], dtype=jnp.int32)
elif isinstance(timesteps, jnp.ndarray) and len(timesteps.shape) == 0:
timesteps = timesteps.astype(dtype=jnp.float32)
timesteps = jnp.expand_dims(timesteps, 0)
t_emb = self.time_proj(timesteps)
t_emb = self.time_embedding(t_emb)
# additional embeddings
aug_emb = None
if self.addition_embed_type == "text_time":
if added_cond_kwargs is None:
raise ValueError(
f"Need to provide argument `added_cond_kwargs` for {self.__class__} when using `addition_embed_type={self.addition_embed_type}`"
)
text_embeds = added_cond_kwargs.get("text_embeds")
if text_embeds is None:
raise ValueError(
f"{self.__class__} has the config param `addition_embed_type` set to 'text_time' which requires the keyword argument `text_embeds` to be passed in `added_cond_kwargs`"
)
time_ids = added_cond_kwargs.get("time_ids")
if time_ids is None:
raise ValueError(
f"{self.__class__} has the config param `addition_embed_type` set to 'text_time' which requires the keyword argument `time_ids` to be passed in `added_cond_kwargs`"
)
# compute time embeds
time_embeds = self.add_time_proj(jnp.ravel(time_ids)) # (1, 6) => (6,) => (6, 256)
time_embeds = jnp.reshape(time_embeds, (text_embeds.shape[0], -1))
add_embeds = jnp.concatenate([text_embeds, time_embeds], axis=-1)
aug_emb = self.add_embedding(add_embeds)
t_emb = t_emb + aug_emb if aug_emb is not None else t_emb
# 2. pre-process
sample = jnp.transpose(sample, (0, 2, 3, 1))
sample = self.conv_in(sample)
# 3. down
down_block_res_samples = (sample,)
for down_block in self.down_blocks:
if isinstance(down_block, FlaxCrossAttnDownBlock2D):
sample, res_samples = down_block(sample, t_emb, encoder_hidden_states, deterministic=not train)
else:
sample, res_samples = down_block(sample, t_emb, deterministic=not train)
down_block_res_samples += res_samples
if down_block_additional_residuals is not None:
new_down_block_res_samples = ()
for down_block_res_sample, down_block_additional_residual in zip(
down_block_res_samples, down_block_additional_residuals
):
down_block_res_sample += down_block_additional_residual
new_down_block_res_samples += (down_block_res_sample,)
down_block_res_samples = new_down_block_res_samples
# 4. mid
if self.mid_block is not None:
sample = self.mid_block(sample, t_emb, encoder_hidden_states, deterministic=not train)
if mid_block_additional_residual is not None:
sample += mid_block_additional_residual
# 5. up
for up_block in self.up_blocks:
res_samples = down_block_res_samples[-(self.layers_per_block + 1) :]
down_block_res_samples = down_block_res_samples[: -(self.layers_per_block + 1)]
if isinstance(up_block, FlaxCrossAttnUpBlock2D):
sample = up_block(
sample,
temb=t_emb,
encoder_hidden_states=encoder_hidden_states,
res_hidden_states_tuple=res_samples,
deterministic=not train,
)
else:
sample = up_block(sample, temb=t_emb, res_hidden_states_tuple=res_samples, deterministic=not train)
# 6. post-process
sample = self.conv_norm_out(sample)
sample = nn.silu(sample)
sample = self.conv_out(sample)
sample = jnp.transpose(sample, (0, 3, 1, 2))
if not return_dict:
return (sample,)
return FlaxUNet2DConditionOutput(sample=sample)
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