modeling_tf_segformer.py

# coding=utf-8
# Copyright 2022 NVIDIA 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.
""" TensorFlow SegFormer model."""


from __future__ import annotations

import math
from typing import Optional, Tuple, Union

import tensorflow as tf

from ...activations_tf import get_tf_activation
from ...file_utils import (
    add_code_sample_docstrings,
    add_start_docstrings,
    add_start_docstrings_to_model_forward,
    replace_return_docstrings,
)
from ...modeling_tf_outputs import TFBaseModelOutput, TFSemanticSegmenterOutput, TFSequenceClassifierOutput
from ...modeling_tf_utils import TFPreTrainedModel, TFSequenceClassificationLoss, keras_serializable, unpack_inputs
from ...tf_utils import shape_list, stable_softmax
from ...utils import logging
from .configuration_segformer import SegformerConfig


logger = logging.get_logger(__name__)

# General docstring
_CONFIG_FOR_DOC = "SegformerConfig"

# Base docstring
_CHECKPOINT_FOR_DOC = "nvidia/mit-b0"
_EXPECTED_OUTPUT_SHAPE = [1, 256, 16, 16]

# Image classification docstring
_IMAGE_CLASS_CHECKPOINT = "nvidia/mit-b0"
_IMAGE_CLASS_EXPECTED_OUTPUT = "tabby, tabby cat"

TF_SEGFORMER_PRETRAINED_MODEL_ARCHIVE_LIST = [
    "nvidia/segformer-b0-finetuned-ade-512-512",
    # See all SegFormer models at https://huggingface.co/models?filter=segformer
]


# Copied from transformers.models.convnext.modeling_tf_convnext.TFConvNextDropPath with ConvNext->Segformer
class TFSegformerDropPath(tf.keras.layers.Layer):
    """Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks).
    References:
        (1) github.com:rwightman/pytorch-image-models
    """

    def __init__(self, drop_path, **kwargs):
        super().__init__(**kwargs)
        self.drop_path = drop_path

    def call(self, x, training=None):
        if training:
            keep_prob = 1 - self.drop_path
            shape = (tf.shape(x)[0],) + (1,) * (len(tf.shape(x)) - 1)
            random_tensor = keep_prob + tf.random.uniform(shape, 0, 1)
            random_tensor = tf.floor(random_tensor)
            return (x / keep_prob) * random_tensor
        return x


class TFSegformerOverlapPatchEmbeddings(tf.keras.layers.Layer):
    """Construct the overlapping patch embeddings."""

    def __init__(self, patch_size, stride, hidden_size, **kwargs):
        super().__init__(**kwargs)
        self.padding = tf.keras.layers.ZeroPadding2D(padding=patch_size // 2)
        self.proj = tf.keras.layers.Conv2D(
            filters=hidden_size, kernel_size=patch_size, strides=stride, padding="VALID", name="proj"
        )

        self.layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-05, name="layer_norm")

    def call(self, pixel_values: tf.Tensor) -> Tuple[tf.Tensor, int, int]:
        embeddings = self.proj(self.padding(pixel_values))
        height = shape_list(embeddings)[1]
        width = shape_list(embeddings)[2]
        hidden_dim = shape_list(embeddings)[3]
        # (batch_size, height, width, num_channels) -> (batch_size, height*width, num_channels)
        # this can be fed to a Transformer layer
        embeddings = tf.reshape(embeddings, (-1, height * width, hidden_dim))
        embeddings = self.layer_norm(embeddings)
        return embeddings, height, width


class TFSegformerEfficientSelfAttention(tf.keras.layers.Layer):
    """SegFormer's efficient self-attention mechanism. Employs the sequence reduction process introduced in the [PvT
    paper](https://arxiv.org/abs/2102.12122)."""

    def __init__(
        self,
        config: SegformerConfig,
        hidden_size: int,
        num_attention_heads: int,
        sequence_reduction_ratio: int,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.hidden_size = hidden_size
        self.num_attention_heads = num_attention_heads

        if self.hidden_size % self.num_attention_heads != 0:
            raise ValueError(
                f"The hidden size ({self.hidden_size}) is not a multiple of the number of attention "
                f"heads ({self.num_attention_heads})"
            )

        self.attention_head_size = self.hidden_size // self.num_attention_heads
        self.all_head_size = self.num_attention_heads * self.attention_head_size
        self.sqrt_att_head_size = math.sqrt(self.attention_head_size)

        self.query = tf.keras.layers.Dense(self.all_head_size, name="query")
        self.key = tf.keras.layers.Dense(self.all_head_size, name="key")
        self.value = tf.keras.layers.Dense(self.all_head_size, name="value")

        self.dropout = tf.keras.layers.Dropout(config.attention_probs_dropout_prob)

        self.sr_ratio = sequence_reduction_ratio
        if sequence_reduction_ratio > 1:
            self.sr = tf.keras.layers.Conv2D(
                filters=hidden_size, kernel_size=sequence_reduction_ratio, strides=sequence_reduction_ratio, name="sr"
            )
            self.layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-05, name="layer_norm")

    def transpose_for_scores(self, tensor: tf.Tensor) -> tf.Tensor:
        # Reshape from [batch_size, seq_length, all_head_size]
        # to [batch_size, seq_length, num_attention_heads, attention_head_size]
        batch_size = shape_list(tensor)[0]
        tensor = tf.reshape(tensor=tensor, shape=(batch_size, -1, self.num_attention_heads, self.attention_head_size))

        # Transpose the tensor from [batch_size, seq_length, num_attention_heads, attention_head_size]
        # to [batch_size, num_attention_heads, seq_length, attention_head_size]
        return tf.transpose(tensor, perm=[0, 2, 1, 3])

    def call(
        self,
        hidden_states: tf.Tensor,
        height: int,
        width: int,
        output_attentions: bool = False,
        training: bool = False,
    ) -> Union[tf.Tensor, Tuple[tf.Tensor, tf.Tensor]]:
        batch_size = shape_list(hidden_states)[0]
        num_channels = shape_list(hidden_states)[2]

        query_layer = self.transpose_for_scores(self.query(hidden_states))

        if self.sr_ratio > 1:
            # Reshape to (batch_size, height, width, num_channels)
            hidden_states = tf.reshape(hidden_states, (batch_size, height, width, num_channels))
            # Apply sequence reduction
            hidden_states = self.sr(hidden_states)
            # Reshape back to (batch_size, seq_len, num_channels)
            hidden_states = tf.reshape(hidden_states, (batch_size, -1, num_channels))
            hidden_states = self.layer_norm(hidden_states)

        key_layer = self.transpose_for_scores(self.key(hidden_states))
        value_layer = self.transpose_for_scores(self.value(hidden_states))

        # Take the dot product between "query" and "key" to get the raw attention scores.
        attention_scores = tf.matmul(query_layer, key_layer, transpose_b=True)

        scale = tf.cast(self.sqrt_att_head_size, dtype=attention_scores.dtype)
        attention_scores = tf.divide(attention_scores, scale)

        # Normalize the attention scores to probabilities.
        attention_probs = stable_softmax(logits=attention_scores, axis=-1)

        # This is actually dropping out entire tokens to attend to, which might
        # seem a bit unusual, but is taken from the original Transformer paper.
        attention_probs = self.dropout(attention_probs, training=training)

        context_layer = tf.matmul(attention_probs, value_layer)

        context_layer = tf.transpose(context_layer, perm=[0, 2, 1, 3])
        # (batch_size, seq_len_q, all_head_size)
        context_layer = tf.reshape(context_layer, (batch_size, -1, self.all_head_size))

        outputs = (context_layer, attention_probs) if output_attentions else (context_layer,)
        return outputs


class TFSegformerSelfOutput(tf.keras.layers.Layer):
    def __init__(self, config: SegformerConfig, hidden_size: int, **kwargs):
        super().__init__(**kwargs)
        self.dense = tf.keras.layers.Dense(hidden_size, name="dense")
        self.dropout = tf.keras.layers.Dropout(config.hidden_dropout_prob)

    def call(self, hidden_states: tf.Tensor, training: bool = False) -> tf.Tensor:
        hidden_states = self.dense(hidden_states)
        hidden_states = self.dropout(hidden_states, training=training)
        return hidden_states


class TFSegformerAttention(tf.keras.layers.Layer):
    def __init__(
        self,
        config: SegformerConfig,
        hidden_size: int,
        num_attention_heads: int,
        sequence_reduction_ratio: int,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.self = TFSegformerEfficientSelfAttention(
            config=config,
            hidden_size=hidden_size,
            num_attention_heads=num_attention_heads,
            sequence_reduction_ratio=sequence_reduction_ratio,
            name="self",
        )
        self.dense_output = TFSegformerSelfOutput(config, hidden_size=hidden_size, name="output")

    def call(
        self, hidden_states: tf.Tensor, height: int, width: int, output_attentions: bool = False
    ) -> Union[tf.Tensor, Tuple[tf.Tensor, tf.Tensor]]:
        self_outputs = self.self(hidden_states, height, width, output_attentions)

        attention_output = self.dense_output(self_outputs[0])
        outputs = (attention_output,) + self_outputs[1:]  # add attentions if we output them
        return outputs


class TFSegformerDWConv(tf.keras.layers.Layer):
    def __init__(self, dim: int = 768, **kwargs):
        super().__init__(**kwargs)
        self.depthwise_convolution = tf.keras.layers.Conv2D(
            filters=dim, kernel_size=3, strides=1, padding="same", groups=dim, name="dwconv"
        )

    def call(self, hidden_states: tf.Tensor, height: int, width: int) -> tf.Tensor:
        batch_size = shape_list(hidden_states)[0]
        num_channels = shape_list(hidden_states)[-1]
        hidden_states = tf.reshape(hidden_states, (batch_size, height, width, num_channels))
        hidden_states = self.depthwise_convolution(hidden_states)

        new_height = shape_list(hidden_states)[1]
        new_width = shape_list(hidden_states)[2]
        num_channels = shape_list(hidden_states)[3]
        hidden_states = tf.reshape(hidden_states, (batch_size, new_height * new_width, num_channels))
        return hidden_states


class TFSegformerMixFFN(tf.keras.layers.Layer):
    def __init__(
        self,
        config: SegformerConfig,
        in_features: int,
        hidden_features: int = None,
        out_features: int = None,
        **kwargs,
    ):
        super().__init__(**kwargs)
        out_features = out_features or in_features
        self.dense1 = tf.keras.layers.Dense(hidden_features, name="dense1")
        self.depthwise_convolution = TFSegformerDWConv(hidden_features, name="dwconv")
        if isinstance(config.hidden_act, str):
            self.intermediate_act_fn = get_tf_activation(config.hidden_act)
        else:
            self.intermediate_act_fn = config.hidden_act
        self.dense2 = tf.keras.layers.Dense(out_features, name="dense2")
        self.dropout = tf.keras.layers.Dropout(config.hidden_dropout_prob)

    def call(self, hidden_states: tf.Tensor, height: int, width: int, training: bool = False) -> tf.Tensor:
        hidden_states = self.dense1(hidden_states)
        hidden_states = self.depthwise_convolution(hidden_states, height, width)
        hidden_states = self.intermediate_act_fn(hidden_states)
        hidden_states = self.dropout(hidden_states, training=training)
        hidden_states = self.dense2(hidden_states)
        hidden_states = self.dropout(hidden_states, training=training)
        return hidden_states


class TFSegformerLayer(tf.keras.layers.Layer):
    """This corresponds to the Block class in the original implementation."""

    def __init__(
        self,
        config,
        hidden_size: int,
        num_attention_heads: int,
        drop_path: float,
        sequence_reduction_ratio: int,
        mlp_ratio: int,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.layer_norm_1 = tf.keras.layers.LayerNormalization(epsilon=1e-05, name="layer_norm_1")
        self.attention = TFSegformerAttention(
            config,
            hidden_size=hidden_size,
            num_attention_heads=num_attention_heads,
            sequence_reduction_ratio=sequence_reduction_ratio,
            name="attention",
        )
        self.drop_path = TFSegformerDropPath(drop_path) if drop_path > 0.0 else tf.keras.layers.Activation("linear")
        self.layer_norm_2 = tf.keras.layers.LayerNormalization(epsilon=1e-05, name="layer_norm_2")
        mlp_hidden_size = int(hidden_size * mlp_ratio)
        self.mlp = TFSegformerMixFFN(config, in_features=hidden_size, hidden_features=mlp_hidden_size, name="mlp")

    def call(
        self,
        hidden_states: tf.Tensor,
        height: int,
        width: int,
        output_attentions: bool = False,
        training: bool = False,
    ) -> Tuple:
        self_attention_outputs = self.attention(
            self.layer_norm_1(hidden_states),  # in Segformer, layernorm is applied before self-attention
            height,
            width,
            output_attentions=output_attentions,
            training=training,
        )

        attention_output = self_attention_outputs[0]
        outputs = self_attention_outputs[1:]  # add self attentions if we output attention weights

        # first residual connection (with stochastic depth)
        attention_output = self.drop_path(attention_output, training=training)
        hidden_states = attention_output + hidden_states
        mlp_output = self.mlp(self.layer_norm_2(hidden_states), height, width)

        # second residual connection (with stochastic depth)
        mlp_output = self.drop_path(mlp_output, training=training)
        layer_output = mlp_output + hidden_states

        outputs = (layer_output,) + outputs

        return outputs


class TFSegformerEncoder(tf.keras.layers.Layer):
    def __init__(self, config: SegformerConfig, **kwargs):
        super().__init__(**kwargs)
        self.config = config

        # stochastic depth decay rule
        drop_path_decays = [x.numpy() for x in tf.linspace(0.0, config.drop_path_rate, sum(config.depths))]

        # patch embeddings
        embeddings = []
        for i in range(config.num_encoder_blocks):
            embeddings.append(
                TFSegformerOverlapPatchEmbeddings(
                    patch_size=config.patch_sizes[i],
                    stride=config.strides[i],
                    hidden_size=config.hidden_sizes[i],
                    name=f"patch_embeddings.{i}",
                )
            )
        self.embeddings = embeddings

        # Transformer blocks
        blocks = []
        cur = 0
        for i in range(config.num_encoder_blocks):
            # each block consists of layers
            layers = []
            if i != 0:
                cur += config.depths[i - 1]
            for j in range(config.depths[i]):
                layers.append(
                    TFSegformerLayer(
                        config,
                        hidden_size=config.hidden_sizes[i],
                        num_attention_heads=config.num_attention_heads[i],
                        drop_path=drop_path_decays[cur + j],
                        sequence_reduction_ratio=config.sr_ratios[i],
                        mlp_ratio=config.mlp_ratios[i],
                        name=f"block.{i}.{j}",
                    )
                )
            blocks.append(layers)

        self.block = blocks

        # Layer norms
        self.layer_norms = [
            tf.keras.layers.LayerNormalization(epsilon=1e-05, name=f"layer_norm.{i}")
            for i in range(config.num_encoder_blocks)
        ]

    def call(
        self,
        pixel_values: tf.Tensor,
        output_attentions: Optional[bool] = False,
        output_hidden_states: Optional[bool] = False,
        return_dict: Optional[bool] = True,
        training: bool = False,
    ) -> Union[Tuple, TFBaseModelOutput]:
        all_hidden_states = () if output_hidden_states else None
        all_self_attentions = () if output_attentions else None

        batch_size = shape_list(pixel_values)[0]

        hidden_states = pixel_values
        for idx, x in enumerate(zip(self.embeddings, self.block, self.layer_norms)):
            embedding_layer, block_layer, norm_layer = x
            # first, obtain patch embeddings
            hidden_states, height, width = embedding_layer(hidden_states)

            # second, send embeddings through blocks
            # (each block consists of multiple layers i.e., list of layers)
            for i, blk in enumerate(block_layer):
                layer_outputs = blk(
                    hidden_states,
                    height,
                    width,
                    output_attentions,
                    training=training,
                )
                hidden_states = layer_outputs[0]
                if output_attentions:
                    all_self_attentions = all_self_attentions + (layer_outputs[1],)

            # third, apply layer norm
            hidden_states = norm_layer(hidden_states)

            # fourth, optionally reshape back to (batch_size, height, width, num_channels)
            if idx != len(self.embeddings) - 1 or (idx == len(self.embeddings) - 1 and self.config.reshape_last_stage):
                num_channels = shape_list(hidden_states)[-1]
                hidden_states = tf.reshape(hidden_states, (batch_size, height, width, num_channels))

            if output_hidden_states:
                all_hidden_states = all_hidden_states + (hidden_states,)

        if not return_dict:
            return tuple(v for v in [hidden_states, all_hidden_states, all_self_attentions] if v is not None)
        return TFBaseModelOutput(
            last_hidden_state=hidden_states, hidden_states=all_hidden_states, attentions=all_self_attentions
        )


@keras_serializable
class TFSegformerMainLayer(tf.keras.layers.Layer):
    config_class = SegformerConfig

    def __init__(self, config: SegformerConfig, **kwargs):
        super().__init__(**kwargs)

        self.config = config
        # hierarchical Transformer encoder
        self.encoder = TFSegformerEncoder(config, name="encoder")

    @unpack_inputs
    def call(
        self,
        pixel_values: tf.Tensor,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
        training: bool = False,
    ) -> Union[Tuple, TFBaseModelOutput]:
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        # When running on CPU, `tf.keras.layers.Conv2D` doesn't support `NCHW` format.
        # So change the input format from `NCHW` to `NHWC`.
        # shape = (batch_size, in_height, in_width, in_channels=num_channels)
        pixel_values = tf.transpose(pixel_values, perm=(0, 2, 3, 1))

        encoder_outputs = self.encoder(
            pixel_values,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
            training=training,
        )
        sequence_output = encoder_outputs[0]
        # Change to NCHW output format to have uniformity in the modules
        sequence_output = tf.transpose(sequence_output, perm=[0, 3, 1, 2])

        # Change the other hidden state outputs to NCHW as well
        if output_hidden_states:
            hidden_states = tuple([tf.transpose(h, perm=(0, 3, 1, 2)) for h in encoder_outputs[1]])

        if not return_dict:
            if tf.greater(len(encoder_outputs[1:]), 0):
                transposed_encoder_outputs = tuple(tf.transpose(v, perm=[0, 3, 1, 2]) for v in encoder_outputs[1:][0])
                return (sequence_output,) + (transposed_encoder_outputs,)
            else:
                return (sequence_output,) + encoder_outputs[1:]

        return TFBaseModelOutput(
            last_hidden_state=sequence_output,
            hidden_states=hidden_states if output_hidden_states else encoder_outputs.hidden_states,
            attentions=encoder_outputs.attentions,
        )


class TFSegformerPreTrainedModel(TFPreTrainedModel):
    """
    An abstract class to handle weights initialization and a simple interface for downloading and loading pretrained
    models.
    """

    config_class = SegformerConfig
    base_model_prefix = "segformer"
    main_input_name = "pixel_values"

    @property
    def input_signature(self):
        return {"pixel_values": tf.TensorSpec(shape=(None, self.config.num_channels, 512, 512), dtype=tf.float32)}


SEGFORMER_START_DOCSTRING = r"""
    This model inherits from [`TFPreTrainedModel`]. Check the superclass documentation for the generic methods the
    library implements for all its model (such as downloading or saving, resizing the input embeddings, pruning heads
    etc.)

    This model is also a [tf.keras.Model](https://www.tensorflow.org/api_docs/python/tf/keras/Model) subclass. Use it
    as a regular TF 2.0 Keras Model and refer to the TF 2.0 documentation for all matter related to general usage and
    behavior.

    Parameters:
        config ([`SegformerConfig`]): Model configuration class with all the parameters of the model.
            Initializing with a config file does not load the weights associated with the model, only the
            configuration. Check out the [`~TFPreTrainedModel.from_pretrained`] method to load the model weights.
"""

SEGFORMER_INPUTS_DOCSTRING = r"""

    Args:
        pixel_values (`np.ndarray`, `tf.Tensor`, `List[tf.Tensor]` ``Dict[str, tf.Tensor]` or `Dict[str, np.ndarray]` and each example must have the shape `(batch_size, num_channels, height, width)`):
            Pixel values. Pixel values can be obtained using [`AutoImageProcessor`]. See
            [`SegformerImageProcessor.__call__`] for details.

        output_attentions (`bool`, *optional*):
            Whether or not to return the attentions tensors of all attention layers. See `attentions` under returned
            tensors for more detail. This argument can be used only in eager mode, in graph mode the value in the
            config will be used instead.

        output_hidden_states (`bool`, *optional*):
            Whether or not to return the hidden states of all layers. See `hidden_states` under returned tensors for
            more detail. This argument can be used only in eager mode, in graph mode the value in the config will be
            used instead.

        return_dict (`bool`, *optional*):
            Whether or not to return a [`~utils.ModelOutput`] instead of a plain tuple. This argument can be used in
            eager mode, in graph mode the value will always be set to True.

        training (`bool`, *optional*, defaults to `False``):
            Whether or not to use the model in training mode (some modules like dropout modules have different
            behaviors between training and evaluation).
"""


@add_start_docstrings(
    "The bare SegFormer encoder (Mix-Transformer) outputting raw hidden-states without any specific head on top.",
    SEGFORMER_START_DOCSTRING,
)
class TFSegformerModel(TFSegformerPreTrainedModel):
    def __init__(self, config: SegformerConfig, *inputs, **kwargs):
        super().__init__(config, *inputs, **kwargs)
        self.config = config

        # hierarchical Transformer encoder
        self.segformer = TFSegformerMainLayer(config, name="segformer")

    @unpack_inputs
    @add_start_docstrings_to_model_forward(SEGFORMER_INPUTS_DOCSTRING.format("(batch_size, sequence_length)"))
    @add_code_sample_docstrings(
        checkpoint=_CHECKPOINT_FOR_DOC,
        output_type=TFBaseModelOutput,
        config_class=_CONFIG_FOR_DOC,
        modality="vision",
        expected_output=_EXPECTED_OUTPUT_SHAPE,
    )
    def call(
        self,
        pixel_values: tf.Tensor,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
        training: bool = False,
    ) -> Union[Tuple, TFBaseModelOutput]:
        outputs = self.segformer(
            pixel_values,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
            training=training,
        )
        return outputs


@add_start_docstrings(
    """
    SegFormer Model transformer with an image classification head on top (a linear layer on top of the final hidden
    states) e.g. for ImageNet.
    """,
    SEGFORMER_START_DOCSTRING,
)
class TFSegformerForImageClassification(TFSegformerPreTrainedModel, TFSequenceClassificationLoss):
    def __init__(self, config: SegformerConfig, *inputs, **kwargs):
        super().__init__(config, *inputs, **kwargs)

        self.num_labels = config.num_labels
        self.segformer = TFSegformerMainLayer(config, name="segformer")

        # Classifier head
        self.classifier = tf.keras.layers.Dense(config.num_labels, name="classifier")

    @unpack_inputs
    @add_start_docstrings_to_model_forward(SEGFORMER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @add_code_sample_docstrings(
        checkpoint=_IMAGE_CLASS_CHECKPOINT,
        output_type=TFSequenceClassifierOutput,
        config_class=_CONFIG_FOR_DOC,
        expected_output=_IMAGE_CLASS_EXPECTED_OUTPUT,
    )
    def call(
        self,
        pixel_values: tf.Tensor | None = None,
        labels: tf.Tensor | None = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, TFSequenceClassifierOutput]:
        outputs = self.segformer(
            pixel_values,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        sequence_output = outputs[0]

        # convert last hidden states to (batch_size, height*width, hidden_size)
        batch_size = shape_list(sequence_output)[0]
        sequence_output = tf.transpose(sequence_output, perm=[0, 2, 3, 1])
        sequence_output = tf.reshape(sequence_output, (batch_size, -1, self.config.hidden_sizes[-1]))

        # global average pooling
        sequence_output = tf.reduce_mean(sequence_output, axis=1)

        logits = self.classifier(sequence_output)

        loss = None if labels is None else self.hf_compute_loss(labels=labels, logits=logits)

        if not return_dict:
            output = (logits,) + outputs[1:]
            return ((loss,) + output) if loss is not None else output

        return TFSequenceClassifierOutput(
            loss=loss, logits=logits, hidden_states=outputs.hidden_states, attentions=outputs.attentions
        )


class TFSegformerMLP(tf.keras.layers.Layer):
    """
    Linear Embedding.
    """

    def __init__(self, config: SegformerConfig, **kwargs):
        super().__init__(**kwargs)
        self.proj = tf.keras.layers.Dense(config.decoder_hidden_size, name="proj")

    def call(self, hidden_states: tf.Tensor) -> tf.Tensor:
        height = shape_list(hidden_states)[1]
        width = shape_list(hidden_states)[2]
        hidden_dim = shape_list(hidden_states)[-1]
        hidden_states = tf.reshape(hidden_states, (-1, height * width, hidden_dim))
        hidden_states = self.proj(hidden_states)
        return hidden_states


class TFSegformerDecodeHead(TFSegformerPreTrainedModel):
    def __init__(self, config: SegformerConfig, **kwargs):
        super().__init__(config, **kwargs)
        # linear layers which will unify the channel dimension of each of the encoder blocks to the same config.decoder_hidden_size
        mlps = []
        for i in range(config.num_encoder_blocks):
            mlp = TFSegformerMLP(config, name=f"linear_c.{i}")
            mlps.append(mlp)
        self.mlps = mlps

        # the following 3 layers implement the ConvModule of the original implementation
        self.linear_fuse = tf.keras.layers.Conv2D(
            filters=config.decoder_hidden_size, kernel_size=1, use_bias=False, name="linear_fuse"
        )
        self.batch_norm = tf.keras.layers.BatchNormalization(epsilon=1e-5, momentum=0.9, name="batch_norm")
        self.activation = tf.keras.layers.Activation("relu")

        self.dropout = tf.keras.layers.Dropout(config.classifier_dropout_prob)
        self.classifier = tf.keras.layers.Conv2D(filters=config.num_labels, kernel_size=1, name="classifier")

        self.config = config

    def call(self, encoder_hidden_states: tf.Tensor, training: bool = False) -> tf.Tensor:
        all_hidden_states = ()
        for encoder_hidden_state, mlp in zip(encoder_hidden_states, self.mlps):
            if self.config.reshape_last_stage is False and len(shape_list(encoder_hidden_state)) == 3:
                height = tf.math.sqrt(tf.cast(shape_list(encoder_hidden_state)[1], tf.float32))
                height = width = tf.cast(height, tf.int32)
                channel_dim = shape_list(encoder_hidden_state)[-1]
                encoder_hidden_state = tf.reshape(encoder_hidden_state, (-1, height, width, channel_dim))

            # unify channel dimension
            encoder_hidden_state = tf.transpose(encoder_hidden_state, perm=[0, 2, 3, 1])
            height, width = shape_list(encoder_hidden_state)[1:3]
            encoder_hidden_state = mlp(encoder_hidden_state)
            channel_dim = shape_list(encoder_hidden_state)[-1]
            encoder_hidden_state = tf.reshape(encoder_hidden_state, (-1, height, width, channel_dim))

            # upsample
            temp_state = tf.transpose(encoder_hidden_states[0], perm=[0, 2, 3, 1])
            upsample_resolution = shape_list(temp_state)[1:-1]
            encoder_hidden_state = tf.image.resize(encoder_hidden_state, size=upsample_resolution, method="bilinear")
            all_hidden_states += (encoder_hidden_state,)

        hidden_states = self.linear_fuse(tf.concat(all_hidden_states[::-1], axis=-1))
        hidden_states = self.batch_norm(hidden_states, training=training)
        hidden_states = self.activation(hidden_states)
        hidden_states = self.dropout(hidden_states, training=training)

        # logits of shape (batch_size, height/4, width/4, num_labels)
        logits = self.classifier(hidden_states)

        return logits


@add_start_docstrings(
    """SegFormer Model transformer with an all-MLP decode head on top e.g. for ADE20k, CityScapes.""",
    SEGFORMER_START_DOCSTRING,
)
class TFSegformerForSemanticSegmentation(TFSegformerPreTrainedModel):
    def __init__(self, config: SegformerConfig, **kwargs):
        super().__init__(config, **kwargs)
        self.segformer = TFSegformerMainLayer(config, name="segformer")
        self.decode_head = TFSegformerDecodeHead(config, name="decode_head")

    def hf_compute_loss(self, logits, labels):
        # upsample logits to the images' original size
        # `labels` is of shape (batch_size, height, width)
        label_interp_shape = shape_list(labels)[1:]

        upsampled_logits = tf.image.resize(logits, size=label_interp_shape, method="bilinear")
        # compute weighted loss
        loss_fct = tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True, reduction="none")

        def masked_loss(real, pred):
            unmasked_loss = loss_fct(real, pred)
            mask = tf.cast(real != self.config.semantic_loss_ignore_index, dtype=unmasked_loss.dtype)
            masked_loss = unmasked_loss * mask
            # Reduction strategy in the similar spirit with
            # https://github.com/huggingface/transformers/blob/main/src/transformers/modeling_tf_utils.py#L210
            reduced_masked_loss = tf.reduce_sum(masked_loss) / tf.reduce_sum(mask)
            return tf.reshape(reduced_masked_loss, (1,))

        return masked_loss(labels, upsampled_logits)

    @unpack_inputs
    @add_start_docstrings_to_model_forward(SEGFORMER_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=TFSemanticSegmenterOutput, config_class=_CONFIG_FOR_DOC)
    def call(
        self,
        pixel_values: tf.Tensor,
        labels: tf.Tensor | None = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, TFSemanticSegmenterOutput]:
        r"""
        labels (`tf.Tensor` of shape `(batch_size, height, width)`, *optional*):
            Ground truth semantic segmentation maps for computing the loss. Indices should be in `[0, ...,
            config.num_labels - 1]`. If `config.num_labels > 1`, a (per-pixel) classification loss is computed
            (Cross-Entropy).

        Returns:

        Examples:

        ```python
        >>> from transformers import AutoImageProcessor, TFSegformerForSemanticSegmentation
        >>> from PIL import Image
        >>> import requests

        >>> url = "http://images.cocodataset.org/val2017/000000039769.jpg"
        >>> image = Image.open(requests.get(url, stream=True).raw)

        >>> image_processor = AutoImageProcessor.from_pretrained("nvidia/segformer-b0-finetuned-ade-512-512")
        >>> model = TFSegformerForSemanticSegmentation.from_pretrained("nvidia/segformer-b0-finetuned-ade-512-512")

        >>> inputs = image_processor(images=image, return_tensors="tf")
        >>> outputs = model(**inputs, training=False)
        >>> # logits are of shape (batch_size, num_labels, height/4, width/4)
        >>> logits = outputs.logits
        >>> list(logits.shape)
        [1, 150, 128, 128]
        ```"""
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )

        outputs = self.segformer(
            pixel_values,
            output_attentions=output_attentions,
            output_hidden_states=True,  # we need the intermediate hidden states
            return_dict=return_dict,
        )

        encoder_hidden_states = outputs.hidden_states if return_dict else outputs[1]

        logits = self.decode_head(encoder_hidden_states)

        loss = None
        if labels is not None:
            if not self.config.num_labels > 1:
                raise ValueError("The number of labels should be greater than one")
            else:
                loss = self.hf_compute_loss(logits=logits, labels=labels)

        # make logits of shape (batch_size, num_labels, height, width) to
        # keep them consistent across APIs
        logits = tf.transpose(logits, perm=[0, 3, 1, 2])

        if not return_dict:
            if output_hidden_states:
                output = (logits,) + outputs[1:]
            else:
                output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return TFSemanticSegmenterOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states if output_hidden_states else None,
            attentions=outputs.attentions,
        )