从DETR到Mask2former(2): 损失函数loss function

DETR的损失函数包括几个部分，如果只看论文或者代码，比较难理解，最好是可以打断点调试，对照着论文看。但是现在DETR模型都已经被集成进各种框架中，很难进入内部打断掉调试。与此同时，数据的label的前处理也比较麻烦。本文中提供的代码做好了数据标签的预处理，可以在中间打断点调试，观察每部分损失函数究竟是如何计算的。

首先，从hugging face的transformers库中拿出detr segmentation的model，并准备数据，数据是coco dataset数据集的panoptic，根据coco的json文件和mask图片，制作label：

from transformers import DetrConfig, DetrForSegmentation

model = DetrForSegmentation.from_pretrained("facebook/detr-resnet-50-panoptic")
state_dict = model.state_dict()
# Remove class weights
del state_dict["detr.class_labels_classifier.weight"]
del state_dict["detr.class_labels_classifier.bias"]
# define new model with custom class classifier
config = DetrConfig.from_pretrained("facebook/detr-resnet-50-panoptic", num_labels=250)
model.load_state_dict(state_dict, strict=False)
model.to("cuda")


# print(model.config)

import torch
import json
from pathlib import Path
from PIL import Image
from transformers import DetrFeatureExtractor
import numpy as np
import matplotlib.pyplot as plt


class CocoPanoptic(torch.utils.data.Dataset):
    def __init__(self, img_folder, ann_folder, ann_file, feature_extractor):
        with open(ann_file, 'r') as f:
            self.coco = json.load(f)

        # sort 'images' field so that they are aligned with 'annotations'
        # i.e., in alphabetical order
        self.coco['images'] = sorted(self.coco['images'], key=lambda x: x['id'])
        # sanity check
        if "annotations" in self.coco:
            for img, ann in zip(self.coco['images'], self.coco['annotations']):
                assert img['file_name'][:-4] == ann['file_name'][:-4]

        self.img_folder = img_folder
        self.ann_folder = Path(ann_folder)
        self.ann_file = ann_file
        self.feature_extractor = feature_extractor

    def __getitem__(self, idx):
        ann_info = self.coco['annotations'][idx] if "annotations" in self.coco else self.coco['images'][idx]
        img_path = Path(self.img_folder) / ann_info['file_name'].replace('.png', '.jpg')

        img = Image.open(img_path).convert('RGB')
        width = 400
        height = 600
        img = img.resize((width, height))
        
        # preprocess image and target (converting target to DETR format, resizing + normalization of both image and target)
        encoding = self.feature_extractor(images=img, annotations=ann_info, masks_path=self.ann_folder, return_tensors="pt")
        pixel_values = encoding["pixel_values"].squeeze() # remove batch dimension
        target = encoding["labels"][0] # remove batch dimension

        return pixel_values, target

    def __len__(self):
        return len(self.coco['images'])


# we reduce the size and max_size to be able to fit the batches in GPU memory
feature_extractor = DetrFeatureExtractor.from_pretrained("facebook/detr-resnet-50-panoptic", size=500, max_size=600)

dataset = CocoPanoptic(img_folder='/home/robotics/Downloads/coco2017/val2017',
                             ann_folder='/home/robotics/Downloads/coco2017/Mask/panoptic mask/panoptic_val2017',     # mask folder path
                             ann_file='/home/robotics/Downloads/coco2017/annotations/panoptic_val2017.json',
                             feature_extractor=feature_extractor)

# let's split it up into very tiny training and validation sets using random indices
np.random.seed(42)
indices = np.random.randint(low=0, high=len(dataset), size=50)
train_dataset = torch.utils.data.Subset(dataset, indices[:40])
val_dataset = torch.utils.data.Subset(dataset, indices[40:])

pixel_values, target = train_dataset[2]
print(pixel_values.shape)
print(target.keys())
# label_masks = target["masks"]
# boxes = target["boxes"]
# labels = target["class_labels"]

from torch.utils.data import DataLoader


def collate_fn(batch):
    pixel_values = [item[0] for item in batch]
    encoded_input = feature_extractor.pad(pixel_values, return_tensors="pt")
    labels = [item[1] for item in batch]
    batch = {}
    batch['pixel_values'] = encoded_input['pixel_values']
    batch['pixel_mask'] = encoded_input['pixel_mask']
    batch['labels'] = labels
    return batch


train_dataloader = DataLoader(train_dataset, collate_fn=collate_fn, batch_size=2, shuffle=True)
val_dataloader = DataLoader(val_dataset, collate_fn=collate_fn, batch_size=1)

# for idx, batch in enumerate(train_dataloader):
#     pixel_values = batch["pixel_values"].to("cuda")
#     pixel_mask = batch["pixel_mask"].to("cuda")
#     labels = [{k: v.to("cuda") for k, v in t.items()} for t in batch["labels"]]
#
#     outputs = model(pixel_values=pixel_values, pixel_mask=pixel_mask, labels=labels)
#
#     loss = outputs.loss
#     loss_dict = outputs.loss_dict
#
#     print("done")

然后再创建一个py文件，写入下面的代码，就可以打断点观察loss的计算了：

import torch.nn as nn
from collections import OrderedDict
import importlib.util
import torch
from torch import Tensor
from scipy.optimize import linear_sum_assignment
from typing import Dict, List, Optional, Tuple


# docstyle-ignore
SCIPY_IMPORT_ERROR = """
{0} requires the scipy library but it was not found in your environment. You can install it with pip:
`pip install scipy`
"""
def is_scipy_available():
    return importlib.util.find_spec("scipy") is not None

BACKENDS_MAPPING = OrderedDict(
    [
        ("scipy", (is_scipy_available, SCIPY_IMPORT_ERROR)),
    ]
)


def requires_backends(obj, backends):
    if not isinstance(backends, (list, tuple)):
        backends = [backends]

    name = obj.__name__ if hasattr(obj, "__name__") else obj.__class__.__name__
    checks = (BACKENDS_MAPPING[backend] for backend in backends)
    failed = [msg.format(name) for available, msg in checks if not available()]
    if failed:
        raise ImportError("".join(failed))


def _upcast(t: Tensor) -> Tensor:
    # Protects from numerical overflows in multiplications by upcasting to the equivalent higher type
    if t.is_floating_point():
        return t if t.dtype in (torch.float32, torch.float64) else t.float()
    else:
        return t if t.dtype in (torch.int32, torch.int64) else t.int()
    

def box_area(boxes: Tensor) -> Tensor:
    """
    Computes the area of a set of bounding boxes, which are specified by its (x1, y1, x2, y2) coordinates.

    Args:
        boxes (`torch.FloatTensor` of shape `(number_of_boxes, 4)`):
            Boxes for which the area will be computed. They are expected to be in (x1, y1, x2, y2) format with `0 <= x1
            < x2` and `0 <= y1 < y2`.

    Returns:
        `torch.FloatTensor`: a tensor containing the area for each box.
    """
    boxes = _upcast(boxes)
    return (boxes[:, 2] - boxes[:, 0]) * (boxes[:, 3] - boxes[:, 1])


def box_iou(boxes1, boxes2):
    area1 = box_area(boxes1)
    area2 = box_area(boxes2)

    left_top = torch.max(boxes1[:, None, :2], boxes2[:, :2])  # [N,M,2]
    right_bottom = torch.min(boxes1[:, None, 2:], boxes2[:, 2:])  # [N,M,2]

    width_height = (right_bottom - left_top).clamp(min=0)  # [N,M,2]
    inter = width_height[:, :, 0] * width_height[:, :, 1]  # [N,M]

    union = area1[:, None] + area2 - inter

    iou = inter / union
    return iou, union


def generalized_box_iou(boxes1, boxes2):
    """
    Generalized IoU from https://giou.stanford.edu/. The boxes should be in [x0, y0, x1, y1] (corner) format.

    Returns:
        `torch.FloatTensor`: a [N, M] pairwise matrix, where N = len(boxes1) and M = len(boxes2)
    """
    # degenerate boxes gives inf / nan results
    # so do an early check
    assert (boxes1[:, 2:] >= boxes1[:, :2]).all()
    assert (boxes2[:, 2:] >= boxes2[:, :2]).all()
    iou, union = box_iou(boxes1, boxes2)

    lt = torch.min(boxes1[:, None, :2], boxes2[:, :2])
    rb = torch.max(boxes1[:, None, 2:], boxes2[:, 2:])

    wh = (rb - lt).clamp(min=0)  # [N,M,2]
    area = wh[:, :, 0] * wh[:, :, 1]

    return iou - (area - union) / area

def center_to_corners_format(x):
    """
    Converts a PyTorch tensor of bounding boxes of center format (center_x, center_y, width, height) to corners format
    (x_0, y_0, x_1, y_1).
    """
    x_c, y_c, w, h = x.unbind(-1)
    b = [(x_c - 0.5 * w), (y_c - 0.5 * h), (x_c + 0.5 * w), (y_c + 0.5 * h)]
    return torch.stack(b, dim=-1)


class DetrHungarianMatcher(nn.Module):
    """
    This class computes an assignment between the targets and the predictions of the network.

    For efficiency reasons, the targets don't include the no_object. Because of this, in general, there are more
    predictions than targets. In this case, we do a 1-to-1 matching of the best predictions, while the others are
    un-matched (and thus treated as non-objects).

    Args:
        class_cost:
            The relative weight of the classification error in the matching cost.
        bbox_cost:
            The relative weight of the L1 error of the bounding box coordinates in the matching cost.
        giou_cost:
            The relative weight of the giou loss of the bounding box in the matching cost.
    """

    def __init__(self, class_cost: float = 1, bbox_cost: float = 1, giou_cost: float = 1):
        super().__init__()
        requires_backends(self, ["scipy"])

        self.class_cost = class_cost
        self.bbox_cost = bbox_cost
        self.giou_cost = giou_cost
        if class_cost == 0 or bbox_cost == 0 or giou_cost == 0:
            raise ValueError("All costs of the Matcher can't be 0")

    @torch.no_grad()
    def forward(self, outputs, targets):
        """
        Args:
            outputs (`dict`):
                A dictionary that contains at least these entries:
                * "logits": Tensor of dim [batch_size, num_queries, num_classes] with the classification logits
                * "pred_boxes": Tensor of dim [batch_size, num_queries, 4] with the predicted box coordinates.
            targets (`List[dict]`):
                A list of targets (len(targets) = batch_size), where each target is a dict containing:
                * "class_labels": Tensor of dim [num_target_boxes] (where num_target_boxes is the number of
                  ground-truth
                 objects in the target) containing the class labels
                * "boxes": Tensor of dim [num_target_boxes, 4] containing the target box coordinates.

        Returns:
            `List[Tuple]`: A list of size `batch_size`, containing tuples of (index_i, index_j) where:
            - index_i is the indices of the selected predictions (in order)
            - index_j is the indices of the corresponding selected targets (in order)
            For each batch element, it holds: len(index_i) = len(index_j) = min(num_queries, num_target_boxes)
        """
        batch_size, num_queries = outputs["logits"].shape[:2]

        # We flatten to compute the cost matrices in a batch
        out_prob = outputs["logits"].flatten(0, 1).softmax(-1)  # [batch_size * num_queries, num_classes]
        out_bbox = outputs["pred_boxes"].flatten(0, 1)  # [batch_size * num_queries, 4]

        # Also concat the target labels and boxes
        tgt_ids = torch.cat([v["class_labels"] for v in targets])
        tgt_bbox = torch.cat([v["boxes"] for v in targets])

        # Compute the classification cost. Contrary to the loss, we don't use the NLL,
        # but approximate it in 1 - proba[target class].
        # The 1 is a constant that doesn't change the matching, it can be ommitted.
        class_cost = -out_prob[:, tgt_ids]

        # Compute the L1 cost between boxes
        bbox_cost = torch.cdist(out_bbox, tgt_bbox, p=1)

        # Compute the giou cost between boxes
        giou_cost = -generalized_box_iou(center_to_corners_format(out_bbox), center_to_corners_format(tgt_bbox))

        # Final cost matrix
        cost_matrix = self.bbox_cost * bbox_cost + self.class_cost * class_cost + self.giou_cost * giou_cost
        cost_matrix = cost_matrix.view(batch_size, num_queries, -1).cpu()

        sizes = [len(v["boxes"]) for v in targets]
        indices = [linear_sum_assignment(c[i]) for i, c in enumerate(cost_matrix.split(sizes, -1))]
        return [(torch.as_tensor(i, dtype=torch.int64), torch.as_tensor(j, dtype=torch.int64)) for i, j in indices]


def _max_by_axis(the_list):
    # type: (List[List[int]]) -> List[int]
    maxes = the_list[0]
    for sublist in the_list[1:]:
        for index, item in enumerate(sublist):
            maxes[index] = max(maxes[index], item)
    return maxes


class NestedTensor(object):
    def __init__(self, tensors, mask: Optional[Tensor]):
        self.tensors = tensors
        self.mask = mask

    def to(self, device):
        cast_tensor = self.tensors.to(device)
        mask = self.mask
        if mask is not None:
            cast_mask = mask.to(device)
        else:
            cast_mask = None
        return NestedTensor(cast_tensor, cast_mask)

    def decompose(self):
        return self.tensors, self.mask

    def __repr__(self):
        return str(self.tensors)


def nested_tensor_from_tensor_list(tensor_list: List[Tensor]):
    if tensor_list[0].ndim == 3:
        max_size = _max_by_axis([list(img.shape) for img in tensor_list])
        batch_shape = [len(tensor_list)] + max_size
        b, c, h, w = batch_shape
        dtype = tensor_list[0].dtype
        device = tensor_list[0].device
        tensor = torch.zeros(batch_shape, dtype=dtype, device=device)
        mask = torch.ones((b, h, w), dtype=torch.bool, device=device)
        for img, pad_img, m in zip(tensor_list, tensor, mask):
            pad_img[: img.shape[0], : img.shape[1], : img.shape[2]].copy_(img)
            m[: img.shape[1], : img.shape[2]] = False
    else:
        raise ValueError("Only 3-dimensional tensors are supported")
    return NestedTensor(tensor, mask)


def sigmoid_focal_loss(inputs, targets, num_boxes, alpha: float = 0.25, gamma: float = 2):
    """
    Loss used in RetinaNet for dense detection: https://arxiv.org/abs/1708.02002.

    Args:
        inputs: A float tensor of arbitrary shape.
                The predictions for each example.
        targets: A float tensor with the same shape as inputs. Stores the binary
                 classification label for each element in inputs (0 for the negative class and 1 for the positive
                 class).
        alpha: (optional) Weighting factor in range (0,1) to balance
                positive vs negative examples. Default = -1 (no weighting).
        gamma: Exponent of the modulating factor (1 - p_t) to
               balance easy vs hard examples.

    Returns:
        Loss tensor
    """
    prob = inputs.sigmoid()
    ce_loss = nn.functional.binary_cross_entropy_with_logits(inputs, targets, reduction="none")
    p_t = prob * targets + (1 - prob) * (1 - targets)
    loss = ce_loss * ((1 - p_t) ** gamma)

    if alpha >= 0:
        alpha_t = alpha * targets + (1 - alpha) * (1 - targets)
        loss = alpha_t * loss

    return loss.mean(1).sum() / num_boxes


def dice_loss(inputs, targets, num_boxes):
    """
    Compute the DICE loss, similar to generalized IOU for masks

    Args:
        inputs: A float tensor of arbitrary shape.
                The predictions for each example.
        targets: A float tensor with the same shape as inputs. Stores the binary
                 classification label for each element in inputs (0 for the negative class and 1 for the positive
                 class).
    """
    inputs = inputs.sigmoid()
    inputs = inputs.flatten(1)
    numerator = 2 * (inputs * targets).sum(1)
    denominator = inputs.sum(-1) + targets.sum(-1)
    loss = 1 - (numerator + 1) / (denominator + 1)
    return loss.sum() / num_boxes


class DetrLoss(nn.Module):
    """
    This class computes the losses for DetrForObjectDetection/DetrForSegmentation. The process happens in two steps: 1)
    we compute hungarian assignment between ground truth boxes and the outputs of the model 2) we supervise each pair
    of matched ground-truth / prediction (supervise class and box).

    A note on the `num_classes` argument (copied from original repo in detr.py): "the naming of the `num_classes`
    parameter of the criterion is somewhat misleading. It indeed corresponds to `max_obj_id` + 1, where `max_obj_id` is
    the maximum id for a class in your dataset. For example, COCO has a `max_obj_id` of 90, so we pass `num_classes` to
    be 91. As another example, for a dataset that has a single class with `id` 1, you should pass `num_classes` to be 2
    (`max_obj_id` + 1). For more details on this, check the following discussion
    https://github.com/facebookresearch/detr/issues/108#issuecomment-650269223"


    Args:
        matcher (`DetrHungarianMatcher`):
            Module able to compute a matching between targets and proposals.
        num_classes (`int`):
            Number of object categories, omitting the special no-object category.
        eos_coef (`float`):
            Relative classification weight applied to the no-object category.
        losses (`List[str]`):
            List of all the losses to be applied. See `get_loss` for a list of all available losses.
    """

    def __init__(self, matcher, num_classes, eos_coef, losses):
        super().__init__()
        self.matcher = matcher
        self.num_classes = num_classes
        self.eos_coef = eos_coef
        self.losses = losses
        empty_weight = torch.ones(self.num_classes + 1)
        empty_weight[-1] = self.eos_coef
        self.register_buffer("empty_weight", empty_weight)

    # removed logging parameter, which was part of the original implementation
    def loss_labels(self, outputs, targets, indices, num_boxes):
        """
        Classification loss (NLL) targets dicts must contain the key "class_labels" containing a tensor of dim
        [nb_target_boxes]
        """
        if "logits" not in outputs:
            raise KeyError("No logits were found in the outputs")
        src_logits = outputs["logits"]

        idx = self._get_src_permutation_idx(indices)
        target_classes_o = torch.cat([t["class_labels"][J] for t, (_, J) in zip(targets, indices)])
        target_classes = torch.full(
            src_logits.shape[:2], self.num_classes, dtype=torch.int64, device=src_logits.device
        )
        target_classes[idx] = target_classes_o

        loss_ce = nn.functional.cross_entropy(src_logits.transpose(1, 2), target_classes, self.empty_weight)
        losses = {"loss_ce": loss_ce}

        return losses

    @torch.no_grad()
    def loss_cardinality(self, outputs, targets, indices, num_boxes):
        """
        Compute the cardinality error, i.e. the absolute error in the number of predicted non-empty boxes.

        This is not really a loss, it is intended for logging purposes only. It doesn't propagate gradients.
        """
        logits = outputs["logits"]
        device = logits.device
        tgt_lengths = torch.as_tensor([len(v["class_labels"]) for v in targets], device=device)
        # Count the number of predictions that are NOT "no-object" (which is the last class)
        card_pred = (logits.argmax(-1) != logits.shape[-1] - 1).sum(1)
        card_err = nn.functional.l1_loss(card_pred.float(), tgt_lengths.float())
        losses = {"cardinality_error": card_err}
        return losses

    def loss_boxes(self, outputs, targets, indices, num_boxes):
        """
        Compute the losses related to the bounding boxes, the L1 regression loss and the GIoU loss.

        Targets dicts must contain the key "boxes" containing a tensor of dim [nb_target_boxes, 4]. The target boxes
        are expected in format (center_x, center_y, w, h), normalized by the image size.
        """
        if "pred_boxes" not in outputs:
            raise KeyError("No predicted boxes found in outputs")
        idx = self._get_src_permutation_idx(indices)
        src_boxes = outputs["pred_boxes"][idx]
        target_boxes = torch.cat([t["boxes"][i] for t, (_, i) in zip(targets, indices)], dim=0)

        loss_bbox = nn.functional.l1_loss(src_boxes, target_boxes, reduction="none")

        losses = {}
        losses["loss_bbox"] = loss_bbox.sum() / num_boxes

        loss_giou = 1 - torch.diag(
            generalized_box_iou(center_to_corners_format(src_boxes), center_to_corners_format(target_boxes))
        )
        losses["loss_giou"] = loss_giou.sum() / num_boxes
        return losses

    def loss_masks(self, outputs, targets, indices, num_boxes):
        """
        Compute the losses related to the masks: the focal loss and the dice loss.

        Targets dicts must contain the key "masks" containing a tensor of dim [nb_target_boxes, h, w].
        """
        if "pred_masks" not in outputs:
            raise KeyError("No predicted masks found in outputs")

        src_idx = self._get_src_permutation_idx(indices)
        tgt_idx = self._get_tgt_permutation_idx(indices)
        src_masks = outputs["pred_masks"]
        src_masks = src_masks[src_idx]
        masks = [t["masks"] for t in targets]
        # TODO use valid to mask invalid areas due to padding in loss
        target_masks, valid = nested_tensor_from_tensor_list(masks).decompose()
        target_masks = target_masks.to(src_masks)
        target_masks = target_masks[tgt_idx]

        # upsample predictions to the target size
        src_masks = nn.functional.interpolate(
            src_masks[:, None], size=target_masks.shape[-2:], mode="bilinear", align_corners=False
        )
        src_masks = src_masks[:, 0].flatten(1)

        target_masks = target_masks.flatten(1)
        target_masks = target_masks.view(src_masks.shape)
        losses = {
            "loss_mask": sigmoid_focal_loss(src_masks, target_masks, num_boxes),
            "loss_dice": dice_loss(src_masks, target_masks, num_boxes),
        }
        return losses

    def _get_src_permutation_idx(self, indices):
        # permute predictions following indices
        batch_idx = torch.cat([torch.full_like(src, i) for i, (src, _) in enumerate(indices)])
        src_idx = torch.cat([src for (src, _) in indices])
        return batch_idx, src_idx

    def _get_tgt_permutation_idx(self, indices):
        # permute targets following indices
        batch_idx = torch.cat([torch.full_like(tgt, i) for i, (_, tgt) in enumerate(indices)])
        tgt_idx = torch.cat([tgt for (_, tgt) in indices])
        return batch_idx, tgt_idx

    def get_loss(self, loss, outputs, targets, indices, num_boxes):
        loss_map = {
            "labels": self.loss_labels,
            "cardinality": self.loss_cardinality,
            "boxes": self.loss_boxes,
            "masks": self.loss_masks,
        }
        if loss not in loss_map:
            raise ValueError(f"Loss {loss} not supported")
        return loss_map[loss](outputs, targets, indices, num_boxes)

    def forward(self, outputs, targets):
        """
        This performs the loss computation.

        Args:
             outputs (`dict`, *optional*):
                Dictionary of tensors, see the output specification of the model for the format.
             targets (`List[dict]`, *optional*):
                List of dicts, such that len(targets) == batch_size. The expected keys in each dict depends on the
                losses applied, see each loss' doc.
        """
        outputs_without_aux = {k: v for k, v in outputs.items() if k != "auxiliary_outputs"}

        # Retrieve the matching between the outputs of the last layer and the targets
        indices = self.matcher(outputs_without_aux, targets)

        # Compute the average number of target boxes accross all nodes, for normalization purposes
        num_boxes = sum(len(t["class_labels"]) for t in targets)
        num_boxes = torch.as_tensor([num_boxes], dtype=torch.float, device=next(iter(outputs.values())).device)
        # (Niels): comment out function below, distributed training to be added
        # if is_dist_avail_and_initialized():
        #     torch.distributed.all_reduce(num_boxes)
        # (Niels) in original implementation, num_boxes is divided by get_world_size()
        num_boxes = torch.clamp(num_boxes, min=1).item()

        # Compute all the requested losses
        losses = {}
        for loss in self.losses:
            losses.update(self.get_loss(loss, outputs, targets, indices, num_boxes))

        # In case of auxiliary losses, we repeat this process with the output of each intermediate layer.
        if "auxiliary_outputs" in outputs:
            for i, auxiliary_outputs in enumerate(outputs["auxiliary_outputs"]):
                indices = self.matcher(auxiliary_outputs, targets)
                for loss in self.losses:
                    if loss == "masks":
                        # Intermediate masks losses are too costly to compute, we ignore them.
                        continue
                    l_dict = self.get_loss(loss, auxiliary_outputs, targets, indices, num_boxes)
                    l_dict = {k + f"_{i}": v for k, v in l_dict.items()}
                    losses.update(l_dict)

        return losses


class_cost = 1
bbox_cost = 5
giou_cost = 2
matcher = DetrHungarianMatcher(
                class_cost=class_cost, bbox_cost=bbox_cost, giou_cost=giou_cost
            )

losses = ["labels", "boxes", "cardinality", "masks"]
num_labels = 250
eos_coefficient = 0.1
criterion = DetrLoss(
    matcher=matcher,
    num_classes=num_labels,
    eos_coef=eos_coefficient,
    losses=losses,
)
criterion.to("cuda")
# Third: compute the losses, based on outputs and labels

from model_from_huggingface import *

for idx, batch in enumerate(train_dataloader):
    pixel_values = batch["pixel_values"].to("cuda")
    pixel_mask = batch["pixel_mask"].to("cuda")
    labels = [{k: v.to("cuda") for k, v in t.items()} for t in batch["labels"]]

    outputs = model(pixel_values=pixel_values, pixel_mask=pixel_mask, labels=labels)


    outputs_loss = {}
    outputs_loss["logits"] = outputs.logits
    outputs_loss["pred_boxes"] = outputs.pred_boxes
    outputs_loss["pred_masks"] = outputs.pred_masks
    loss_dict = criterion(outputs_loss, labels)
    # Fourth: compute total loss, as a weighted sum of the various losses
    bbox_loss_coefficient = 5
    giou_loss_coefficient = 2
    mask_loss_coefficient = 1
    dice_loss_coefficient = 1
    weight_dict = {"loss_ce": 1, "loss_bbox": bbox_loss_coefficient}
    weight_dict["loss_giou"] = giou_loss_coefficient
    weight_dict["loss_mask"] = mask_loss_coefficient
    weight_dict["loss_dice"] = dice_loss_coefficient
    
    loss = sum(loss_dict[k] * weight_dict[k] for k in loss_dict.keys() if k in weight_dict)
    
    print(loss)

下面解释一下运行其中的变量

indices是query和target进行匈牙利匹配后的结果

?

也就是说，第5个query去匹配class_labels中的10