# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved """ DETR model and criterion classes. """ import torch import torch.nn.functional as F from torch import nn from . import box_ops from .misc import (NestedTensor, nested_tensor_from_tensor_list, accuracy, get_world_size, interpolate, is_dist_avail_and_initialized) from .backbone import build_backbone from .matcher import build_matcher from .segmentation import (DETRsegm, PostProcessPanoptic, PostProcessSegm, dice_loss, sigmoid_focal_loss) from .transformer import build_transformer class DETR(nn.Module): """ This is the DETR module that performs object detection """ def __init__(self, backbone, transformer, num_classes, num_queries, aux_loss=False): """ Initializes the model. Parameters: backbone: torch module of the backbone to be used. See backbone.py transformer: torch module of the transformer architecture. See transformer.py num_classes: number of object classes num_queries: number of object queries, ie detection slot. This is the maximal number of objects DETR can detect in a single image. For COCO, we recommend 100 queries. aux_loss: True if auxiliary decoding losses (loss at each decoder layer) are to be used. """ super().__init__() self.num_queries = num_queries self.transformer = transformer hidden_dim = transformer.d_model self.class_embed = nn.Linear(hidden_dim, num_classes + 1) self.bbox_embed = MLP(hidden_dim, hidden_dim, 4, 3) self.query_embed = nn.Embedding(num_queries, hidden_dim) self.input_proj = nn.Conv2d(backbone.num_channels, hidden_dim, kernel_size=1) self.backbone = backbone self.aux_loss = aux_loss def forward(self, samples: NestedTensor): """ The forward expects a NestedTensor, which consists of: - samples.tensor: batched images, of shape [batch_size x 3 x H x W] - samples.mask: a binary mask of shape [batch_size x H x W], containing 1 on padded pixels It returns a dict with the following elements: - "pred_logits": the classification logits (including no-object) for all queries. Shape= [batch_size x num_queries x (num_classes + 1)] - "pred_boxes": The normalized boxes coordinates for all queries, represented as (center_x, center_y, height, width). These values are normalized in [0, 1], relative to the size of each individual image (disregarding possible padding). See PostProcess for information on how to retrieve the unnormalized bounding box. - "aux_outputs": Optional, only returned when auxilary losses are activated. It is a list of dictionnaries containing the two above keys for each decoder layer. """ if isinstance(samples, (list, torch.Tensor)): samples = nested_tensor_from_tensor_list(samples) features, pos = self.backbone(samples) src, mask = features[-1].decompose() assert mask is not None hs = self.transformer(self.input_proj(src), mask, self.query_embed.weight, pos[-1])[0] outputs_class = self.class_embed(hs) outputs_coord = self.bbox_embed(hs).sigmoid() out = {'pred_logits': outputs_class[-1], 'pred_boxes': outputs_coord[-1]} if self.aux_loss: out['aux_outputs'] = self._set_aux_loss(outputs_class, outputs_coord) return out @torch.jit.unused def _set_aux_loss(self, outputs_class, outputs_coord): # this is a workaround to make torchscript happy, as torchscript # doesn't support dictionary with non-homogeneous values, such # as a dict having both a Tensor and a list. return [{'pred_logits': a, 'pred_boxes': b} for a, b in zip(outputs_class[:-1], outputs_coord[:-1])] class SetCriterion(nn.Module): """ This class computes the loss for DETR. 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) """ def __init__(self, num_classes, matcher, weight_dict, eos_coef, losses): """ Create the criterion. Parameters: num_classes: number of object categories, omitting the special no-object category matcher: module able to compute a matching between targets and proposals weight_dict: dict containing as key the names of the losses and as values their relative weight. eos_coef: relative classification weight applied to the no-object category losses: list of all the losses to be applied. See get_loss for list of available losses. """ super().__init__() self.num_classes = num_classes self.matcher = matcher self.weight_dict = weight_dict 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) def loss_labels(self, outputs, targets, indices, num_boxes, log=True): """Classification loss (NLL) targets dicts must contain the key "labels" containing a tensor of dim [nb_target_boxes] """ assert 'pred_logits' in outputs src_logits = outputs['pred_logits'] idx = self._get_src_permutation_idx(indices) target_classes_o = torch.cat([t["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 = F.cross_entropy(src_logits.transpose(1, 2), target_classes, self.empty_weight) losses = {'loss_ce': loss_ce} if log: # TODO this should probably be a separate loss, not hacked in this one here losses['class_error'] = 100 - accuracy(src_logits[idx], target_classes_o)[0] return losses @torch.no_grad() def loss_cardinality(self, outputs, targets, indices, num_boxes): """ Compute the cardinality error, ie 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 """ pred_logits = outputs['pred_logits'] device = pred_logits.device tgt_lengths = torch.as_tensor([len(v["labels"]) for v in targets], device=device) # Count the number of predictions that are NOT "no-object" (which is the last class) card_pred = (pred_logits.argmax(-1) != pred_logits.shape[-1] - 1).sum(1) card_err = F.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. """ assert 'pred_boxes' 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 = F.l1_loss(src_boxes, target_boxes, reduction='none') losses = {} losses['loss_bbox'] = loss_bbox.sum() / num_boxes loss_giou = 1 - torch.diag(box_ops.generalized_box_iou( box_ops.box_cxcywh_to_xyxy(src_boxes), box_ops.box_cxcywh_to_xyxy(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] """ assert "pred_masks" 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 = 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, **kwargs): loss_map = { 'labels': self.loss_labels, 'cardinality': self.loss_cardinality, 'boxes': self.loss_boxes, 'masks': self.loss_masks } assert loss in loss_map, f'do you really want to compute {loss} loss?' return loss_map[loss](outputs, targets, indices, num_boxes, **kwargs) def forward(self, outputs, targets): """ This performs the loss computation. Parameters: outputs: dict of tensors, see the output specification of the model for the format targets: 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 != 'aux_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["labels"]) for t in targets) num_boxes = torch.as_tensor([num_boxes], dtype=torch.float, device=next(iter(outputs.values())).device) if is_dist_avail_and_initialized(): torch.distributed.all_reduce(num_boxes) num_boxes = torch.clamp(num_boxes / get_world_size(), 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 'aux_outputs' in outputs: for i, aux_outputs in enumerate(outputs['aux_outputs']): indices = self.matcher(aux_outputs, targets) for loss in self.losses: if loss == 'masks': # Intermediate masks losses are too costly to compute, we ignore them. continue kwargs = {} if loss == 'labels': # Logging is enabled only for the last layer kwargs = {'log': False} l_dict = self.get_loss(loss, aux_outputs, targets, indices, num_boxes, **kwargs) l_dict = {k + f'_{i}': v for k, v in l_dict.items()} losses.update(l_dict) return losses class PostProcess(nn.Module): """ This module converts the model's output into the format expected by the coco api""" @torch.no_grad() def forward(self, outputs, target_sizes): """ Perform the computation Parameters: outputs: raw outputs of the model target_sizes: tensor of dimension [batch_size x 2] containing the size of each images of the batch For evaluation, this must be the original image size (before any data augmentation) For visualization, this should be the image size after data augment, but before padding """ out_logits, out_bbox = outputs['pred_logits'], outputs['pred_boxes'] assert len(out_logits) == len(target_sizes) assert target_sizes.shape[1] == 2 prob = F.softmax(out_logits, -1) scores, labels = prob[..., :-1].max(-1) # convert to [x0, y0, x1, y1] format boxes = box_ops.box_cxcywh_to_xyxy(out_bbox) # and from relative [0, 1] to absolute [0, height] coordinates img_h, img_w = target_sizes.unbind(1) scale_fct = torch.stack([img_w, img_h, img_w, img_h], dim=1) boxes = boxes * scale_fct[:, None, :] results = [{'scores': s, 'labels': l, 'boxes': b} for s, l, b in zip(scores, labels, boxes)] return results class MLP(nn.Module): """ Very simple multi-layer perceptron (also called FFN)""" def __init__(self, input_dim, hidden_dim, output_dim, num_layers): super().__init__() self.num_layers = num_layers h = [hidden_dim] * (num_layers - 1) self.layers = nn.ModuleList(nn.Linear(n, k) for n, k in zip([input_dim] + h, h + [output_dim])) def forward(self, x): for i, layer in enumerate(self.layers): x = F.relu(layer(x)) if i < self.num_layers - 1 else layer(x) return x def build(args): # the `num_classes` naming here 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 num_classes = 20 if args.dataset_file != 'coco' else 91 if args.dataset_file == "coco_panoptic": # for panoptic, we just add a num_classes that is large enough to hold # max_obj_id + 1, but the exact value doesn't really matter num_classes = 250 device = torch.device(args.device) backbone = build_backbone(args) transformer = build_transformer(args) model = DETR( backbone, transformer, num_classes=num_classes, num_queries=args.num_queries, aux_loss=args.aux_loss, ) if args.masks: model = DETRsegm(model, freeze_detr=(args.frozen_weights is not None)) matcher = build_matcher(args) weight_dict = {'loss_ce': 1, 'loss_bbox': args.bbox_loss_coef} weight_dict['loss_giou'] = args.giou_loss_coef if args.masks: weight_dict["loss_mask"] = args.mask_loss_coef weight_dict["loss_dice"] = args.dice_loss_coef # TODO this is a hack if args.aux_loss: aux_weight_dict = {} for i in range(args.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', 'boxes', 'cardinality'] if args.masks: losses += ["masks"] criterion = SetCriterion(num_classes, matcher=matcher, weight_dict=weight_dict, eos_coef=args.eos_coef, losses=losses) criterion.to(device) postprocessors = {'bbox': PostProcess()} if args.masks: postprocessors['segm'] = PostProcessSegm() if args.dataset_file == "coco_panoptic": is_thing_map = {i: i <= 90 for i in range(201)} postprocessors["panoptic"] = PostProcessPanoptic(is_thing_map, threshold=0.85) return model, criterion, postprocessors