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# Copyright (c) Facebook, Inc. and its affiliates.
# Copyright (c) Meta Platforms, Inc. All Rights Reserved
from typing import Tuple
import torch
from torch import nn
from torch.nn import functional as F
from detectron2.config import configurable
from detectron2.data import MetadataCatalog
from detectron2.modeling import META_ARCH_REGISTRY, build_backbone, build_sem_seg_head
from detectron2.modeling.backbone import Backbone
from detectron2.modeling.postprocessing import sem_seg_postprocess
from detectron2.structures import ImageList
from .modeling.criterion import SetCriterion
from .modeling.matcher import HungarianMatcher
@META_ARCH_REGISTRY.register()
class MaskFormer(nn.Module):
"""
Main class for mask classification semantic segmentation architectures.
"""
@configurable
def __init__(
self,
*,
backbone: Backbone,
sem_seg_head: nn.Module,
criterion: nn.Module,
num_queries: int,
panoptic_on: bool,
object_mask_threshold: float,
overlap_threshold: float,
metadata,
size_divisibility: int,
sem_seg_postprocess_before_inference: bool,
pixel_mean: Tuple[float],
pixel_std: Tuple[float],
):
"""
Args:
backbone: a backbone module, must follow detectron2's backbone interface
sem_seg_head: a module that predicts semantic segmentation from backbone features
criterion: a module that defines the loss
num_queries: int, number of queries
panoptic_on: bool, whether to output panoptic segmentation prediction
object_mask_threshold: float, threshold to filter query based on classification score
for panoptic segmentation inference
overlap_threshold: overlap threshold used in general inference for panoptic segmentation
metadata: dataset meta, get `thing` and `stuff` category names for panoptic
segmentation inference
size_divisibility: Some backbones require the input height and width to be divisible by a
specific integer. We can use this to override such requirement.
sem_seg_postprocess_before_inference: whether to resize the prediction back
to original input size before semantic segmentation inference or after.
For high-resolution dataset like Mapillary, resizing predictions before
inference will cause OOM error.
pixel_mean, pixel_std: list or tuple with #channels element, representing
the per-channel mean and std to be used to normalize the input image
"""
super().__init__()
self.backbone = backbone
self.sem_seg_head = sem_seg_head
self.criterion = criterion
self.num_queries = num_queries
self.overlap_threshold = overlap_threshold
self.panoptic_on = panoptic_on
self.object_mask_threshold = object_mask_threshold
self.metadata = metadata
if size_divisibility < 0:
# use backbone size_divisibility if not set
size_divisibility = self.backbone.size_divisibility
self.size_divisibility = size_divisibility
self.sem_seg_postprocess_before_inference = sem_seg_postprocess_before_inference
self.register_buffer(
"pixel_mean", torch.Tensor(pixel_mean).view(-1, 1, 1), False
)
self.register_buffer("pixel_std", torch.Tensor(pixel_std).view(-1, 1, 1), False)
@classmethod
def from_config(cls, cfg):
backbone = build_backbone(cfg)
sem_seg_head = build_sem_seg_head(cfg, backbone.output_shape())
# Loss parameters:
deep_supervision = cfg.MODEL.MASK_FORMER.DEEP_SUPERVISION
no_object_weight = cfg.MODEL.MASK_FORMER.NO_OBJECT_WEIGHT
dice_weight = cfg.MODEL.MASK_FORMER.DICE_WEIGHT
mask_weight = cfg.MODEL.MASK_FORMER.MASK_WEIGHT
# building criterion
matcher = HungarianMatcher(
cost_class=1,
cost_mask=mask_weight,
cost_dice=dice_weight,
)
weight_dict = {"loss_ce": 1, "loss_mask": mask_weight, "loss_dice": dice_weight}
if deep_supervision:
dec_layers = cfg.MODEL.MASK_FORMER.DEC_LAYERS
aux_weight_dict = {}
for i in range(dec_layers - 1):
aux_weight_dict.update({k + f"_{i}": v for k, v in weight_dict.items()})
weight_dict.update(aux_weight_dict)
losses = ["labels", "masks"]
criterion = SetCriterion(
sem_seg_head.num_classes,
matcher=matcher,
weight_dict=weight_dict,
eos_coef=no_object_weight,
losses=losses,
)
return {
"backbone": backbone,
"sem_seg_head": sem_seg_head,
"criterion": criterion,
"num_queries": cfg.MODEL.MASK_FORMER.NUM_OBJECT_QUERIES,
"panoptic_on": cfg.MODEL.MASK_FORMER.TEST.PANOPTIC_ON,
"object_mask_threshold": cfg.MODEL.MASK_FORMER.TEST.OBJECT_MASK_THRESHOLD,
"overlap_threshold": cfg.MODEL.MASK_FORMER.TEST.OVERLAP_THRESHOLD,
"metadata": MetadataCatalog.get(cfg.DATASETS.TRAIN[0]),
"size_divisibility": cfg.MODEL.MASK_FORMER.SIZE_DIVISIBILITY,
"sem_seg_postprocess_before_inference": (
cfg.MODEL.MASK_FORMER.TEST.SEM_SEG_POSTPROCESSING_BEFORE_INFERENCE
or cfg.MODEL.MASK_FORMER.TEST.PANOPTIC_ON
),
"pixel_mean": cfg.MODEL.PIXEL_MEAN,
"pixel_std": cfg.MODEL.PIXEL_STD,
}
@property
def device(self):
return self.pixel_mean.device
def forward(self, batched_inputs):
"""
Args:
batched_inputs: a list, batched outputs of :class:`DatasetMapper`.
Each item in the list contains the inputs for one image.
For now, each item in the list is a dict that contains:
* "image": Tensor, image in (C, H, W) format.
* "instances": per-region ground truth
* Other information that's included in the original dicts, such as:
"height", "width" (int): the output resolution of the model (may be different
from input resolution), used in inference.
Returns:
list[dict]:
each dict has the results for one image. The dict contains the following keys:
* "sem_seg":
A Tensor that represents the
per-pixel segmentation prediced by the head.
The prediction has shape KxHxW that represents the logits of
each class for each pixel.
* "panoptic_seg":
A tuple that represent panoptic output
panoptic_seg (Tensor): of shape (height, width) where the values are ids for each segment.
segments_info (list[dict]): Describe each segment in `panoptic_seg`.
Each dict contains keys "id", "category_id", "isthing".
"""
images = [x["image"].to(self.device) for x in batched_inputs]
images = [(x - self.pixel_mean) / self.pixel_std for x in images]
images = ImageList.from_tensors(images, self.size_divisibility)
features = self.backbone(images.tensor)
outputs = self.sem_seg_head(features)
if self.training:
# mask classification target
if "instances" in batched_inputs[0]:
gt_instances = [x["instances"].to(self.device) for x in batched_inputs]
targets = self.prepare_targets(gt_instances, images)
else:
targets = None
# bipartite matching-based loss
losses = self.criterion(outputs, targets)
for k in list(losses.keys()):
if k in self.criterion.weight_dict:
losses[k] *= self.criterion.weight_dict[k]
else:
# remove this loss if not specified in `weight_dict`
losses.pop(k)
return losses
else:
mask_cls_results = outputs["pred_logits"]
mask_pred_results = outputs["pred_masks"]
# upsample masks
mask_pred_results = F.interpolate(
mask_pred_results,
size=(images.tensor.shape[-2], images.tensor.shape[-1]),
mode="bilinear",
align_corners=False,
)
processed_results = []
for mask_cls_result, mask_pred_result, input_per_image, image_size in zip(
mask_cls_results, mask_pred_results, batched_inputs, images.image_sizes
):
height = input_per_image.get("height", image_size[0])
width = input_per_image.get("width", image_size[1])
if self.sem_seg_postprocess_before_inference:
mask_pred_result = sem_seg_postprocess(
mask_pred_result, image_size, height, width
)
# semantic segmentation inference
r = self.semantic_inference(mask_cls_result, mask_pred_result)
if not self.sem_seg_postprocess_before_inference:
r = sem_seg_postprocess(r, image_size, height, width)
processed_results.append({"sem_seg": r})
# panoptic segmentation inference
if self.panoptic_on:
panoptic_r = self.panoptic_inference(
mask_cls_result, mask_pred_result
)
processed_results[-1]["panoptic_seg"] = panoptic_r
return processed_results
def prepare_targets(self, targets, images):
h, w = images.tensor.shape[-2:]
new_targets = []
for targets_per_image in targets:
# pad gt
gt_masks = targets_per_image.gt_masks
padded_masks = torch.zeros(
(gt_masks.shape[0], h, w), dtype=gt_masks.dtype, device=gt_masks.device
)
padded_masks[:, : gt_masks.shape[1], : gt_masks.shape[2]] = gt_masks
new_targets.append(
{
"labels": targets_per_image.gt_classes,
"masks": padded_masks,
}
)
return new_targets
def semantic_inference(self, mask_cls, mask_pred):
mask_cls = F.softmax(mask_cls, dim=-1)[..., :-1]
mask_pred = mask_pred.sigmoid()
semseg = torch.einsum("qc,qhw->chw", mask_cls, mask_pred)
return semseg
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