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maskformer_head.py
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# Copyright (c) OpenMMLab. All rights reserved.
from typing import List, Tuple
import torch
import torch.nn as nn
import torch.nn.functional as F
try:
from mmdet.models.dense_heads import MaskFormerHead as MMDET_MaskFormerHead
except ModuleNotFoundError:
MMDET_MaskFormerHead = None
from mmengine.structures import InstanceData
from torch import Tensor
from mmseg.registry import MODELS
from mmseg.structures.seg_data_sample import SegDataSample
from mmseg.utils import ConfigType, SampleList
@MODELS.register_module()
class MaskFormerHead(MMDET_MaskFormerHead):
"""Implements the MaskFormer head.
See `Per-Pixel Classification is Not All You Need for Semantic Segmentation
<https://arxiv.org/pdf/2107.06278>`_ for details.
Args:
num_classes (int): Number of classes. Default: 150.
align_corners (bool): align_corners argument of F.interpolate.
Default: False.
ignore_index (int): The label index to be ignored. Default: 255.
"""
def __init__(self,
num_classes: int = 150,
align_corners: bool = False,
ignore_index: int = 255,
**kwargs) -> None:
super().__init__(**kwargs)
self.out_channels = kwargs['out_channels']
self.align_corners = True
self.num_classes = num_classes
self.align_corners = align_corners
self.out_channels = num_classes
self.ignore_index = ignore_index
feat_channels = kwargs['feat_channels']
self.cls_embed = nn.Linear(feat_channels, self.num_classes + 1)
def _seg_data_to_instance_data(self, batch_data_samples: SampleList):
"""Perform forward propagation to convert paradigm from MMSegmentation
to MMDetection to ensure ``MMDET_MaskFormerHead`` could be called
normally. Specifically, ``batch_gt_instances`` would be added.
Args:
batch_data_samples (List[:obj:`SegDataSample`]): The Data
Samples. It usually includes information such as
`gt_sem_seg`.
Returns:
tuple[Tensor]: A tuple contains two lists.
- batch_gt_instances (list[:obj:`InstanceData`]): Batch of
gt_instance. It usually includes ``labels``, each is
unique ground truth label id of images, with
shape (num_gt, ) and ``masks``, each is ground truth
masks of each instances of a image, shape (num_gt, h, w).
- batch_img_metas (list[dict]): List of image meta information.
"""
batch_img_metas = []
batch_gt_instances = []
for data_sample in batch_data_samples:
# Add `batch_input_shape` in metainfo of data_sample, which would
# be used in MaskFormerHead of MMDetection.
metainfo = data_sample.metainfo
metainfo['batch_input_shape'] = metainfo['img_shape']
data_sample.set_metainfo(metainfo)
batch_img_metas.append(data_sample.metainfo)
gt_sem_seg = data_sample.gt_sem_seg.data
classes = torch.unique(
gt_sem_seg,
sorted=False,
return_inverse=False,
return_counts=False)
# remove ignored region
gt_labels = classes[classes != self.ignore_index]
masks = []
for class_id in gt_labels:
masks.append(gt_sem_seg == class_id)
if len(masks) == 0:
gt_masks = torch.zeros((0, gt_sem_seg.shape[-2],
gt_sem_seg.shape[-1])).to(gt_sem_seg)
else:
gt_masks = torch.stack(masks).squeeze(1)
instance_data = InstanceData(
labels=gt_labels, masks=gt_masks.long())
batch_gt_instances.append(instance_data)
return batch_gt_instances, batch_img_metas
def loss(self, x: Tuple[Tensor], batch_data_samples: SampleList,
train_cfg: ConfigType) -> dict:
"""Perform forward propagation and loss calculation of the decoder head
on the features of the upstream network.
Args:
x (tuple[Tensor]): Multi-level features from the upstream
network, each is a 4D-tensor.
batch_data_samples (List[:obj:`SegDataSample`]): The Data
Samples. It usually includes information such as
`gt_sem_seg`.
train_cfg (ConfigType): Training config.
Returns:
dict[str, Tensor]: a dictionary of loss components.
"""
# batch SegDataSample to InstanceDataSample
batch_gt_instances, batch_img_metas = self._seg_data_to_instance_data(
batch_data_samples)
# forward
all_cls_scores, all_mask_preds = self(x, batch_data_samples)
# loss
losses = self.loss_by_feat(all_cls_scores, all_mask_preds,
batch_gt_instances, batch_img_metas)
return losses
def predict(self, x: Tuple[Tensor], batch_img_metas: List[dict],
test_cfg: ConfigType) -> Tuple[Tensor]:
"""Test without augmentaton.
Args:
x (tuple[Tensor]): Multi-level features from the
upstream network, each is a 4D-tensor.
batch_img_metas (List[:obj:`SegDataSample`]): The Data
Samples. It usually includes information such as
`gt_sem_seg`.
test_cfg (ConfigType): Test config.
Returns:
Tensor: A tensor of segmentation mask.
"""
batch_data_samples = []
for metainfo in batch_img_metas:
metainfo['batch_input_shape'] = metainfo['img_shape']
batch_data_samples.append(SegDataSample(metainfo=metainfo))
# Forward function of MaskFormerHead from MMDetection needs
# 'batch_data_samples' as inputs, which is image shape actually.
all_cls_scores, all_mask_preds = self(x, batch_data_samples)
mask_cls_results = all_cls_scores[-1]
mask_pred_results = all_mask_preds[-1]
# upsample masks
img_shape = batch_img_metas[0]['batch_input_shape']
mask_pred_results = F.interpolate(
mask_pred_results,
size=img_shape,
mode='bilinear',
align_corners=False)
# semantic inference
cls_score = F.softmax(mask_cls_results, dim=-1)[..., :-1]
mask_pred = mask_pred_results.sigmoid()
seg_logits = torch.einsum('bqc,bqhw->bchw', cls_score, mask_pred)
return seg_logits