src/lerobot/policies/normalize.py

#!/usr/bin/env python

# Copyright 2024 The HuggingFace Inc. 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 numpy as np
import torch
from torch import Tensor, nn

from lerobot.configs.types import FeatureType, NormalizationMode, PolicyFeature


def create_stats_buffers(
    features: dict[str, PolicyFeature],
    norm_map: dict[str, NormalizationMode],
    stats: dict[str, dict[str, Tensor]] | None = None,
) -> dict[str, dict[str, nn.ParameterDict]]:
    """
    Create buffers per modality (e.g. "observation.image", "action") containing their mean, std, min, max
    statistics.

    Args: (see Normalize and Unnormalize)

    Returns:
        dict: A dictionary where keys are modalities and values are `nn.ParameterDict` containing
            `nn.Parameters` set to `requires_grad=False`, suitable to not be updated during backpropagation.
    """
    stats_buffers = {}

    for key, ft in features.items():
        norm_mode = norm_map.get(ft.type, NormalizationMode.IDENTITY)
        if norm_mode is NormalizationMode.IDENTITY:
            continue

        assert isinstance(norm_mode, NormalizationMode)

        shape = tuple(ft.shape)

        if ft.type is FeatureType.VISUAL:
            # sanity checks
            assert len(shape) == 3, f"number of dimensions of {key} != 3 ({shape=}"
            c, h, w = shape
            assert c < h and c < w, f"{key} is not channel first ({shape=})"
            # override image shape to be invariant to height and width
            shape = (c, 1, 1)

        # Note: we initialize mean, std, min, max to infinity. They should be overwritten
        # downstream by `stats` or `policy.load_state_dict`, as expected. During forward,
        # we assert they are not infinity anymore.

        buffer = {}
        if norm_mode is NormalizationMode.MEAN_STD:
            mean = torch.ones(shape, dtype=torch.float32) * torch.inf
            std = torch.ones(shape, dtype=torch.float32) * torch.inf
            buffer = nn.ParameterDict(
                {
                    "mean": nn.Parameter(mean, requires_grad=False),
                    "std": nn.Parameter(std, requires_grad=False),
                }
            )
        elif norm_mode is NormalizationMode.MIN_MAX:
            min = torch.ones(shape, dtype=torch.float32) * torch.inf
            max = torch.ones(shape, dtype=torch.float32) * torch.inf
            buffer = nn.ParameterDict(
                {
                    "min": nn.Parameter(min, requires_grad=False),
                    "max": nn.Parameter(max, requires_grad=False),
                }
            )

        # TODO(aliberts, rcadene): harmonize this to only use one framework (np or torch)
        if stats:
            if isinstance(stats[key]["mean"], np.ndarray):
                if norm_mode is NormalizationMode.MEAN_STD:
                    buffer["mean"].data = torch.from_numpy(stats[key]["mean"]).to(dtype=torch.float32)
                    buffer["std"].data = torch.from_numpy(stats[key]["std"]).to(dtype=torch.float32)
                elif norm_mode is NormalizationMode.MIN_MAX:
                    buffer["min"].data = torch.from_numpy(stats[key]["min"]).to(dtype=torch.float32)
                    buffer["max"].data = torch.from_numpy(stats[key]["max"]).to(dtype=torch.float32)
            elif isinstance(stats[key]["mean"], torch.Tensor):
                # Note: The clone is needed to make sure that the logic in save_pretrained doesn't see duplicated
                # tensors anywhere (for example, when we use the same stats for normalization and
                # unnormalization). See the logic here
                # https://github.com/huggingface/safetensors/blob/079781fd0dc455ba0fe851e2b4507c33d0c0d407/bindings/python/py_src/safetensors/torch.py#L97.
                if norm_mode is NormalizationMode.MEAN_STD:
                    buffer["mean"].data = stats[key]["mean"].clone().to(dtype=torch.float32)
                    buffer["std"].data = stats[key]["std"].clone().to(dtype=torch.float32)
                elif norm_mode is NormalizationMode.MIN_MAX:
                    buffer["min"].data = stats[key]["min"].clone().to(dtype=torch.float32)
                    buffer["max"].data = stats[key]["max"].clone().to(dtype=torch.float32)
            else:
                type_ = type(stats[key]["mean"])
                raise ValueError(f"np.ndarray or torch.Tensor expected, but type is '{type_}' instead.")

        stats_buffers[key] = buffer
    return stats_buffers


def _no_stats_error_str(name: str) -> str:
    return (
        f"`{name}` is infinity. You should either initialize with `stats` as an argument, or use a "
        "pretrained model."
    )


class Normalize(nn.Module):
    """Normalizes data (e.g. "observation.image") for more stable and faster convergence during training."""

    def __init__(
        self,
        features: dict[str, PolicyFeature],
        norm_map: dict[str, NormalizationMode],
        stats: dict[str, dict[str, Tensor]] | None = None,
    ):
        """
        Args:
            shapes (dict): A dictionary where keys are input modalities (e.g. "observation.image") and values
            are their shapes (e.g. `[3,96,96]`]). These shapes are used to create the tensor buffer containing
            mean, std, min, max statistics. If the provided `shapes` contain keys related to images, the shape
            is adjusted to be invariant to height and width, assuming a channel-first (c, h, w) format.
            modes (dict): A dictionary where keys are output modalities (e.g. "observation.image") and values
                are their normalization modes among:
                    - "mean_std": subtract the mean and divide by standard deviation.
                    - "min_max": map to [-1, 1] range.
            stats (dict, optional): A dictionary where keys are output modalities (e.g. "observation.image")
                and values are dictionaries of statistic types and their values (e.g.
                `{"mean": torch.randn(3,1,1)}, "std": torch.randn(3,1,1)}`). If provided, as expected for
                training the model for the first time, these statistics will overwrite the default buffers. If
                not provided, as expected for finetuning or evaluation, the default buffers should to be
                overwritten by a call to `policy.load_state_dict(state_dict)`. That way, initializing the
                dataset is not needed to get the stats, since they are already in the policy state_dict.
        """
        super().__init__()
        self.features = features
        self.norm_map = norm_map
        self.stats = stats
        stats_buffers = create_stats_buffers(features, norm_map, stats)
        for key, buffer in stats_buffers.items():
            setattr(self, "buffer_" + key.replace(".", "_"), buffer)

    # TODO(rcadene): should we remove torch.no_grad?
    @torch.no_grad()
    def forward(self, batch: dict[str, Tensor]) -> dict[str, Tensor]:
        # TODO: Remove this shallow copy
        batch = dict(batch)  # shallow copy avoids mutating the input batch
        for key, ft in self.features.items():
            if key not in batch:
                # FIXME(aliberts, rcadene): This might lead to silent fail!
                continue

            norm_mode = self.norm_map.get(ft.type, NormalizationMode.IDENTITY)
            if norm_mode is NormalizationMode.IDENTITY:
                continue

            buffer = getattr(self, "buffer_" + key.replace(".", "_"))

            if norm_mode is NormalizationMode.MEAN_STD:
                mean = buffer["mean"]
                std = buffer["std"]
                assert not torch.isinf(mean).any(), _no_stats_error_str("mean")
                assert not torch.isinf(std).any(), _no_stats_error_str("std")
                batch[key] = (batch[key] - mean) / (std + 1e-8)
            elif norm_mode is NormalizationMode.MIN_MAX:
                min = buffer["min"]
                max = buffer["max"]
                assert not torch.isinf(min).any(), _no_stats_error_str("min")
                assert not torch.isinf(max).any(), _no_stats_error_str("max")
                # normalize to [0,1]
                batch[key] = (batch[key] - min) / (max - min + 1e-8)
                # normalize to [-1, 1]
                batch[key] = batch[key] * 2 - 1
            else:
                raise ValueError(norm_mode)
        return batch


class Unnormalize(nn.Module):
    """
    Similar to `Normalize` but unnormalizes output data (e.g. `{"action": torch.randn(b,c)}`) in their
    original range used by the environment.
    """

    def __init__(
        self,
        features: dict[str, PolicyFeature],
        norm_map: dict[str, NormalizationMode],
        stats: dict[str, dict[str, Tensor]] | None = None,
    ):
        """
        Args:
            shapes (dict): A dictionary where keys are input modalities (e.g. "observation.image") and values
            are their shapes (e.g. `[3,96,96]`]). These shapes are used to create the tensor buffer containing
            mean, std, min, max statistics. If the provided `shapes` contain keys related to images, the shape
            is adjusted to be invariant to height and width, assuming a channel-first (c, h, w) format.
            modes (dict): A dictionary where keys are output modalities (e.g. "observation.image") and values
                are their normalization modes among:
                    - "mean_std": subtract the mean and divide by standard deviation.
                    - "min_max": map to [-1, 1] range.
            stats (dict, optional): A dictionary where keys are output modalities (e.g. "observation.image")
                and values are dictionaries of statistic types and their values (e.g.
                `{"mean": torch.randn(3,1,1)}, "std": torch.randn(3,1,1)}`). If provided, as expected for
                training the model for the first time, these statistics will overwrite the default buffers. If
                not provided, as expected for finetuning or evaluation, the default buffers should to be
                overwritten by a call to `policy.load_state_dict(state_dict)`. That way, initializing the
                dataset is not needed to get the stats, since they are already in the policy state_dict.
        """
        super().__init__()
        self.features = features
        self.norm_map = norm_map
        self.stats = stats
        # `self.buffer_observation_state["mean"]` contains `torch.tensor(state_dim)`
        stats_buffers = create_stats_buffers(features, norm_map, stats)
        for key, buffer in stats_buffers.items():
            setattr(self, "buffer_" + key.replace(".", "_"), buffer)

    # TODO(rcadene): should we remove torch.no_grad?
    @torch.no_grad()
    def forward(self, batch: dict[str, Tensor]) -> dict[str, Tensor]:
        batch = dict(batch)  # shallow copy avoids mutating the input batch
        for key, ft in self.features.items():
            if key not in batch:
                continue

            norm_mode = self.norm_map.get(ft.type, NormalizationMode.IDENTITY)
            if norm_mode is NormalizationMode.IDENTITY:
                continue

            buffer = getattr(self, "buffer_" + key.replace(".", "_"))

            if norm_mode is NormalizationMode.MEAN_STD:
                mean = buffer["mean"]
                std = buffer["std"]
                assert not torch.isinf(mean).any(), _no_stats_error_str("mean")
                assert not torch.isinf(std).any(), _no_stats_error_str("std")
                batch[key] = batch[key] * std + mean
            elif norm_mode is NormalizationMode.MIN_MAX:
                min = buffer["min"]
                max = buffer["max"]
                assert not torch.isinf(min).any(), _no_stats_error_str("min")
                assert not torch.isinf(max).any(), _no_stats_error_str("max")
                batch[key] = (batch[key] + 1) / 2
                batch[key] = batch[key] * (max - min) + min
            else:
                raise ValueError(norm_mode)
        return batch


# TODO (azouitine): We should replace all normalization on the policies with register_buffer normalization
#       and remove the `Normalize` and `Unnormalize` classes.
def _initialize_stats_buffers(
    module: nn.Module,
    features: dict[str, PolicyFeature],
    norm_map: dict[str, NormalizationMode],
    stats: dict[str, dict[str, Tensor]] | None = None,
) -> None:
    """Register statistics buffers (mean/std or min/max) on the given *module*.

    The logic matches the previous constructors of `NormalizeBuffer` and `UnnormalizeBuffer`,
    but is factored out so it can be reused by both classes and stay in sync.
    """
    for key, ft in features.items():
        norm_mode = norm_map.get(ft.type, NormalizationMode.IDENTITY)
        if norm_mode is NormalizationMode.IDENTITY:
            continue

        shape: tuple[int, ...] = tuple(ft.shape)
        if ft.type is FeatureType.VISUAL:
            # reduce spatial dimensions, keep channel dimension only
            c, *_ = shape
            shape = (c, 1, 1)

        prefix = key.replace(".", "_")

        if norm_mode is NormalizationMode.MEAN_STD:
            mean = torch.full(shape, torch.inf, dtype=torch.float32)
            std = torch.full(shape, torch.inf, dtype=torch.float32)

            if stats and key in stats and "mean" in stats[key] and "std" in stats[key]:
                mean_data = stats[key]["mean"]
                std_data = stats[key]["std"]
                if isinstance(mean_data, torch.Tensor):
                    # Note: The clone is needed to make sure that the logic in save_pretrained doesn't see duplicated
                    # tensors anywhere (for example, when we use the same stats for normalization and
                    # unnormalization). See the logic here
                    # https://github.com/huggingface/safetensors/blob/079781fd0dc455ba0fe851e2b4507c33d0c0d407/bindings/python/py_src/safetensors/torch.py#L97.
                    mean = mean_data.clone().to(dtype=torch.float32)
                    std = std_data.clone().to(dtype=torch.float32)
                else:
                    raise ValueError(f"Unsupported stats type for key '{key}' (expected ndarray or Tensor).")

            module.register_buffer(f"{prefix}_mean", mean)
            module.register_buffer(f"{prefix}_std", std)
            continue

        if norm_mode is NormalizationMode.MIN_MAX:
            min_val = torch.full(shape, torch.inf, dtype=torch.float32)
            max_val = torch.full(shape, torch.inf, dtype=torch.float32)

            if stats and key in stats and "min" in stats[key] and "max" in stats[key]:
                min_data = stats[key]["min"]
                max_data = stats[key]["max"]
                if isinstance(min_data, torch.Tensor):
                    min_val = min_data.clone().to(dtype=torch.float32)
                    max_val = max_data.clone().to(dtype=torch.float32)
                else:
                    raise ValueError(f"Unsupported stats type for key '{key}' (expected ndarray or Tensor).")

            module.register_buffer(f"{prefix}_min", min_val)
            module.register_buffer(f"{prefix}_max", max_val)
            continue

        raise ValueError(norm_mode)


class NormalizeBuffer(nn.Module):
    """Same as `Normalize` but statistics are stored as registered buffers rather than parameters."""

    def __init__(
        self,
        features: dict[str, PolicyFeature],
        norm_map: dict[str, NormalizationMode],
        stats: dict[str, dict[str, Tensor]] | None = None,
    ):
        super().__init__()
        self.features = features
        self.norm_map = norm_map

        _initialize_stats_buffers(self, features, norm_map, stats)

    def forward(self, batch: dict[str, Tensor]) -> dict[str, Tensor]:
        batch = dict(batch)
        for key, ft in self.features.items():
            if key not in batch:
                continue

            norm_mode = self.norm_map.get(ft.type, NormalizationMode.IDENTITY)
            if norm_mode is NormalizationMode.IDENTITY:
                continue

            prefix = key.replace(".", "_")

            if norm_mode is NormalizationMode.MEAN_STD:
                mean = getattr(self, f"{prefix}_mean")
                std = getattr(self, f"{prefix}_std")
                assert not torch.isinf(mean).any(), _no_stats_error_str("mean")
                assert not torch.isinf(std).any(), _no_stats_error_str("std")
                batch[key] = (batch[key] - mean) / (std + 1e-8)
                continue

            if norm_mode is NormalizationMode.MIN_MAX:
                min_val = getattr(self, f"{prefix}_min")
                max_val = getattr(self, f"{prefix}_max")
                assert not torch.isinf(min_val).any(), _no_stats_error_str("min")
                assert not torch.isinf(max_val).any(), _no_stats_error_str("max")
                batch[key] = (batch[key] - min_val) / (max_val - min_val + 1e-8)
                batch[key] = batch[key] * 2 - 1
                continue

            raise ValueError(norm_mode)

        return batch


class UnnormalizeBuffer(nn.Module):
    """Inverse operation of `NormalizeBuffer`. Uses registered buffers for statistics."""

    def __init__(
        self,
        features: dict[str, PolicyFeature],
        norm_map: dict[str, NormalizationMode],
        stats: dict[str, dict[str, Tensor]] | None = None,
    ):
        super().__init__()
        self.features = features
        self.norm_map = norm_map

        _initialize_stats_buffers(self, features, norm_map, stats)

    def forward(self, batch: dict[str, Tensor]) -> dict[str, Tensor]:
        # batch = dict(batch)
        for key, ft in self.features.items():
            if key not in batch:
                continue

            norm_mode = self.norm_map.get(ft.type, NormalizationMode.IDENTITY)
            if norm_mode is NormalizationMode.IDENTITY:
                continue

            prefix = key.replace(".", "_")

            if norm_mode is NormalizationMode.MEAN_STD:
                mean = getattr(self, f"{prefix}_mean")
                std = getattr(self, f"{prefix}_std")
                assert not torch.isinf(mean).any(), _no_stats_error_str("mean")
                assert not torch.isinf(std).any(), _no_stats_error_str("std")
                batch[key] = batch[key] * std + mean
                continue

            if norm_mode is NormalizationMode.MIN_MAX:
                min_val = getattr(self, f"{prefix}_min")
                max_val = getattr(self, f"{prefix}_max")
                assert not torch.isinf(min_val).any(), _no_stats_error_str("min")
                assert not torch.isinf(max_val).any(), _no_stats_error_str("max")
                batch[key] = (batch[key] + 1) / 2
                batch[key] = batch[key] * (max_val - min_val) + min_val
                continue

            raise ValueError(norm_mode)

        return batch