rfdetr/models/lwdetr.py

# ------------------------------------------------------------------------
# RF-DETR
# Copyright (c) 2025 Roboflow. All Rights Reserved.
# Licensed under the Apache License, Version 2.0 [see LICENSE for details]
# ------------------------------------------------------------------------
# Modified from LW-DETR (https://github.com/Atten4Vis/LW-DETR)
# Copyright (c) 2024 Baidu. All Rights Reserved.
# ------------------------------------------------------------------------
# Modified from Conditional DETR (https://github.com/Atten4Vis/ConditionalDETR)
# Copyright (c) 2021 Microsoft. All Rights Reserved.
# ------------------------------------------------------------------------
# Modified from DETR (https://github.com/facebookresearch/detr)
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
# ------------------------------------------------------------------------
# Modified from Deformable DETR (https://github.com/fundamentalvision/Deformable-DETR)
# Copyright (c) 2020 SenseTime. All Rights Reserved.
# ------------------------------------------------------------------------

"""
LW-DETR model and criterion classes
"""
import copy
import math
from typing import Callable
import torch
import torch.nn.functional as F
from torch import nn

from rfdetr.util import box_ops
from rfdetr.util.misc import (NestedTensor, nested_tensor_from_tensor_list,
                       accuracy, get_world_size,
                       is_dist_avail_and_initialized)

from rfdetr.models.backbone import build_backbone
from rfdetr.models.matcher import build_matcher
from rfdetr.models.transformer import build_transformer

class LWDETR(nn.Module):
    """ This is the Group DETR v3 module that performs object detection """
    def __init__(self,
                 backbone,
                 transformer,
                 num_classes,
                 num_queries,
                 aux_loss=False,
                 group_detr=1,
                 two_stage=False,
                 lite_refpoint_refine=False,
                 bbox_reparam=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
                         Conditional 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.
            group_detr: Number of groups to speed detr training. Default is 1.
            lite_refpoint_refine: TODO
        """
        super().__init__()
        self.num_queries = num_queries
        self.transformer = transformer
        hidden_dim = transformer.d_model
        self.class_embed = nn.Linear(hidden_dim, num_classes)
        self.bbox_embed = MLP(hidden_dim, hidden_dim, 4, 3)

        query_dim=4
        self.refpoint_embed = nn.Embedding(num_queries * group_detr, query_dim)
        self.query_feat = nn.Embedding(num_queries * group_detr, hidden_dim)
        nn.init.constant_(self.refpoint_embed.weight.data, 0)

        self.backbone = backbone
        self.aux_loss = aux_loss
        self.group_detr = group_detr

        # iter update
        self.lite_refpoint_refine = lite_refpoint_refine
        if not self.lite_refpoint_refine:
            self.transformer.decoder.bbox_embed = self.bbox_embed
        else:
            self.transformer.decoder.bbox_embed = None

        self.bbox_reparam = bbox_reparam

        # init prior_prob setting for focal loss
        prior_prob = 0.01
        bias_value = -math.log((1 - prior_prob) / prior_prob)
        self.class_embed.bias.data = torch.ones(num_classes) * bias_value

        # init bbox_mebed
        nn.init.constant_(self.bbox_embed.layers[-1].weight.data, 0)
        nn.init.constant_(self.bbox_embed.layers[-1].bias.data, 0)

        # two_stage
        self.two_stage = two_stage
        if self.two_stage:
            self.transformer.enc_out_bbox_embed = nn.ModuleList(
                [copy.deepcopy(self.bbox_embed) for _ in range(group_detr)])
            self.transformer.enc_out_class_embed = nn.ModuleList(
                [copy.deepcopy(self.class_embed) for _ in range(group_detr)])

        self._export = False

    def reinitialize_detection_head(self, num_classes):
        # Create new classification head
        del self.class_embed
        self.add_module("class_embed", nn.Linear(self.transformer.d_model, num_classes))
        
        # Initialize with focal loss bias adjustment
        prior_prob = 0.01
        bias_value = -math.log((1 - prior_prob) / prior_prob)
        self.class_embed.bias.data = torch.ones(num_classes) * bias_value

        if self.two_stage:
            del self.transformer.enc_out_class_embed
            self.transformer.add_module("enc_out_class_embed", nn.ModuleList(
                [copy.deepcopy(self.class_embed) for _ in range(self.group_detr)]))


    def export(self):
        self._export = True
        self._forward_origin = self.forward
        self.forward = self.forward_export
        for name, m in self.named_modules():
            if hasattr(m, "export") and isinstance(m.export, Callable) and hasattr(m, "_export") and not m._export:
                m.export()

    def forward(self, samples: NestedTensor, targets=None):
        """ 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]
               - "pred_boxes": The normalized boxes coordinates for all queries, represented as
                               (center_x, center_y, width, height). 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, poss = self.backbone(samples)

        srcs = []
        masks = []
        for l, feat in enumerate(features):
            src, mask = feat.decompose()
            srcs.append(src)
            masks.append(mask)
            assert mask is not None

        if self.training:
            refpoint_embed_weight = self.refpoint_embed.weight
            query_feat_weight = self.query_feat.weight
        else:
            # only use one group in inference
            refpoint_embed_weight = self.refpoint_embed.weight[:self.num_queries]
            query_feat_weight = self.query_feat.weight[:self.num_queries]

        hs, ref_unsigmoid, hs_enc, ref_enc = self.transformer(
            srcs, masks, poss, refpoint_embed_weight, query_feat_weight)

        if hs is not None:
            if self.bbox_reparam:
                outputs_coord_delta = self.bbox_embed(hs)
                outputs_coord_cxcy = outputs_coord_delta[..., :2] * ref_unsigmoid[..., 2:] + ref_unsigmoid[..., :2]
                outputs_coord_wh = outputs_coord_delta[..., 2:].exp() * ref_unsigmoid[..., 2:]
                outputs_coord = torch.concat(
                    [outputs_coord_cxcy, outputs_coord_wh], dim=-1
                )
            else:
                outputs_coord = (self.bbox_embed(hs) + ref_unsigmoid).sigmoid()

            outputs_class = self.class_embed(hs)

            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)

        if self.two_stage:
            group_detr = self.group_detr if self.training else 1
            hs_enc_list = hs_enc.chunk(group_detr, dim=1)
            cls_enc = []
            for g_idx in range(group_detr):
                cls_enc_gidx = self.transformer.enc_out_class_embed[g_idx](hs_enc_list[g_idx])
                cls_enc.append(cls_enc_gidx)
            cls_enc = torch.cat(cls_enc, dim=1)
            if hs is not None:
                out['enc_outputs'] = {'pred_logits': cls_enc, 'pred_boxes': ref_enc}
            else:
                out = {'pred_logits': cls_enc, 'pred_boxes': ref_enc}
        
        return out

    def forward_export(self, tensors):
        srcs, _, poss = self.backbone(tensors)
        # only use one group in inference
        refpoint_embed_weight = self.refpoint_embed.weight[:self.num_queries]
        query_feat_weight = self.query_feat.weight[:self.num_queries]

        hs, ref_unsigmoid, hs_enc, ref_enc = self.transformer(
            srcs, None, poss, refpoint_embed_weight, query_feat_weight)

        if hs is not None:
            if self.bbox_reparam:
                outputs_coord_delta = self.bbox_embed(hs)
                outputs_coord_cxcy = outputs_coord_delta[..., :2] * ref_unsigmoid[..., 2:] + ref_unsigmoid[..., :2]
                outputs_coord_wh = outputs_coord_delta[..., 2:].exp() * ref_unsigmoid[..., 2:]
                outputs_coord = torch.concat(
                    [outputs_coord_cxcy, outputs_coord_wh], dim=-1
                )
            else:
                outputs_coord = (self.bbox_embed(hs) + ref_unsigmoid).sigmoid()
            outputs_class = self.class_embed(hs)
        else:
            assert self.two_stage, "if not using decoder, two_stage must be True"
            outputs_class = self.transformer.enc_out_class_embed[0](hs_enc)
            outputs_coord = ref_enc
            
        return outputs_coord, outputs_class

    @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])]

    def update_drop_path(self, drop_path_rate, vit_encoder_num_layers):
        """ """
        dp_rates = [x.item() for x in torch.linspace(0, drop_path_rate, vit_encoder_num_layers)]
        for i in range(vit_encoder_num_layers):
            if hasattr(self.backbone[0].encoder, 'blocks'): # Not aimv2
                if hasattr(self.backbone[0].encoder.blocks[i].drop_path, 'drop_prob'):
                    self.backbone[0].encoder.blocks[i].drop_path.drop_prob = dp_rates[i]
            else: # aimv2
                if hasattr(self.backbone[0].encoder.trunk.blocks[i].drop_path, 'drop_prob'):
                    self.backbone[0].encoder.trunk.blocks[i].drop_path.drop_prob = dp_rates[i]

    def update_dropout(self, drop_rate):
        for module in self.transformer.modules():
            if isinstance(module, nn.Dropout):
                module.p = drop_rate


class SetCriterion(nn.Module):
    """ This class computes the loss for Conditional 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,
                 focal_alpha,
                 losses,
                 group_detr=1,
                 sum_group_losses=False,
                 use_varifocal_loss=False,
                 use_position_supervised_loss=False,
                 ia_bce_loss=False,):
        """ 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.
            losses: list of all the losses to be applied. See get_loss for list of available losses.
            focal_alpha: alpha in Focal Loss
            group_detr: Number of groups to speed detr training. Default is 1.
        """
        super().__init__()
        self.num_classes = num_classes
        self.matcher = matcher
        self.weight_dict = weight_dict
        self.losses = losses
        self.focal_alpha = focal_alpha
        self.group_detr = group_detr
        self.sum_group_losses = sum_group_losses
        self.use_varifocal_loss = use_varifocal_loss
        self.use_position_supervised_loss = use_position_supervised_loss
        self.ia_bce_loss = ia_bce_loss

    def loss_labels(self, outputs, targets, indices, num_boxes, log=True):
        """Classification loss (Binary focal loss)
        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)])

        if self.ia_bce_loss:
            alpha = self.focal_alpha
            gamma = 2 
            src_boxes = outputs['pred_boxes'][idx]
            target_boxes = torch.cat([t['boxes'][i] for t, (_, i) in zip(targets, indices)], dim=0)

            iou_targets=torch.diag(box_ops.box_iou(
                box_ops.box_cxcywh_to_xyxy(src_boxes.detach()),
                box_ops.box_cxcywh_to_xyxy(target_boxes))[0])
            pos_ious = iou_targets.clone().detach()
            prob = src_logits.sigmoid()
            #init positive weights and negative weights
            pos_weights = torch.zeros_like(src_logits)
            neg_weights =  prob ** gamma

            pos_ind=[id for id in idx]
            pos_ind.append(target_classes_o)

            t = prob[pos_ind].pow(alpha) * pos_ious.pow(1 - alpha)
            t = torch.clamp(t, 0.01).detach()

            pos_weights[pos_ind] = t.to(pos_weights.dtype)
            neg_weights[pos_ind] = 1 - t.to(neg_weights.dtype)
            # a reformulation of the standard loss_ce = - pos_weights * prob.log() - neg_weights * (1 - prob).log()
            # with a focus on statistical stability by using fused logsigmoid
            loss_ce = neg_weights * src_logits - F.logsigmoid(src_logits) * (pos_weights + neg_weights)
            loss_ce = loss_ce.sum() / num_boxes

        elif self.use_position_supervised_loss:
            src_boxes = outputs['pred_boxes'][idx]
            target_boxes = torch.cat([t['boxes'][i] for t, (_, i) in zip(targets, indices)], dim=0)

            iou_targets=torch.diag(box_ops.box_iou(
                box_ops.box_cxcywh_to_xyxy(src_boxes.detach()),
                box_ops.box_cxcywh_to_xyxy(target_boxes))[0])
            pos_ious = iou_targets.clone().detach()
            # pos_ious_func = pos_ious ** 2
            pos_ious_func = pos_ious

            cls_iou_func_targets = torch.zeros((src_logits.shape[0], src_logits.shape[1],self.num_classes),
                                        dtype=src_logits.dtype, device=src_logits.device)

            pos_ind=[id for id in idx]
            pos_ind.append(target_classes_o)
            cls_iou_func_targets[pos_ind] = pos_ious_func
            norm_cls_iou_func_targets = cls_iou_func_targets \
                / (cls_iou_func_targets.view(cls_iou_func_targets.shape[0], -1, 1).amax(1, True) + 1e-8)
            loss_ce = position_supervised_loss(src_logits, norm_cls_iou_func_targets, num_boxes, alpha=self.focal_alpha, gamma=2) * src_logits.shape[1]

        elif self.use_varifocal_loss:
            src_boxes = outputs['pred_boxes'][idx]
            target_boxes = torch.cat([t['boxes'][i] for t, (_, i) in zip(targets, indices)], dim=0)

            iou_targets=torch.diag(box_ops.box_iou(
                box_ops.box_cxcywh_to_xyxy(src_boxes.detach()),
                box_ops.box_cxcywh_to_xyxy(target_boxes))[0])
            pos_ious = iou_targets.clone().detach()

            cls_iou_targets = torch.zeros((src_logits.shape[0], src_logits.shape[1],self.num_classes),
                                        dtype=src_logits.dtype, device=src_logits.device)

            pos_ind=[id for id in idx]
            pos_ind.append(target_classes_o)
            cls_iou_targets[pos_ind] = pos_ious
            loss_ce = sigmoid_varifocal_loss(src_logits, cls_iou_targets, num_boxes, alpha=self.focal_alpha, gamma=2) * src_logits.shape[1]
        else:
            target_classes = torch.full(src_logits.shape[:2], self.num_classes,
                                        dtype=torch.int64, device=src_logits.device)
            target_classes[idx] = target_classes_o

            target_classes_onehot = torch.zeros([src_logits.shape[0], src_logits.shape[1], src_logits.shape[2]+1],
                                                dtype=src_logits.dtype, layout=src_logits.layout, device=src_logits.device)
            target_classes_onehot.scatter_(2, target_classes.unsqueeze(-1), 1)

            target_classes_onehot = target_classes_onehot[:,:,:-1]
            loss_ce = sigmoid_focal_loss(src_logits, target_classes_onehot, num_boxes, alpha=self.focal_alpha, gamma=2) * src_logits.shape[1]
        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 _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,
        }
        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
        """
        group_detr = self.group_detr if self.training else 1
        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, group_detr=group_detr)

        # Compute the average number of target boxes accross all nodes, for normalization purposes
        num_boxes = sum(len(t["labels"]) for t in targets)
        if not self.sum_group_losses:
            num_boxes = num_boxes * group_detr
        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, group_detr=group_detr)
                for loss in self.losses:
                    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)

        if 'enc_outputs' in outputs:
            enc_outputs = outputs['enc_outputs']
            indices = self.matcher(enc_outputs, targets, group_detr=group_detr)
            for loss in self.losses:
                kwargs = {}
                if loss == 'labels':
                    # Logging is enabled only for the last layer
                    kwargs['log'] = False
                l_dict = self.get_loss(loss, enc_outputs, targets, indices, num_boxes, **kwargs)
                l_dict = {k + f'_enc': v for k, v in l_dict.items()}
                losses.update(l_dict)

        return losses


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 = F.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 sigmoid_varifocal_loss(inputs, targets, num_boxes, alpha: float = 0.25, gamma: float = 2):
    prob = inputs.sigmoid()
    focal_weight = targets * (targets > 0.0).float() + \
            (1 - alpha) * (prob - targets).abs().pow(gamma) * \
            (targets <= 0.0).float()
    ce_loss = F.binary_cross_entropy_with_logits(inputs, targets, reduction="none")
    loss = ce_loss * focal_weight

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


def position_supervised_loss(inputs, targets, num_boxes, alpha: float = 0.25, gamma: float = 2):
    prob = inputs.sigmoid()
    ce_loss = F.binary_cross_entropy_with_logits(inputs, targets, reduction="none")
    loss = ce_loss * (torch.abs(targets - prob) ** gamma)

    if alpha >= 0:
        alpha_t = alpha * (targets > 0.0).float() + (1 - alpha) * (targets <= 0.0).float()
        loss = alpha_t * loss

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


class PostProcess(nn.Module):
    """ This module converts the model's output into the format expected by the coco api"""
    def __init__(self, num_select=300) -> None:
        super().__init__()
        self.num_select = num_select

    @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 = out_logits.sigmoid()
        topk_values, topk_indexes = torch.topk(prob.view(out_logits.shape[0], -1), self.num_select, dim=1)
        scores = topk_values
        topk_boxes = topk_indexes // out_logits.shape[2]
        labels = topk_indexes % out_logits.shape[2]
        boxes = box_ops.box_cxcywh_to_xyxy(out_bbox)
        boxes = torch.gather(boxes, 1, topk_boxes.unsqueeze(-1).repeat(1,1,4))

        # 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_model(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 = args.num_classes + 1
    device = torch.device(args.device)


    backbone = build_backbone(
        encoder=args.encoder,
        vit_encoder_num_layers=args.vit_encoder_num_layers,
        pretrained_encoder=args.pretrained_encoder,
        window_block_indexes=args.window_block_indexes,
        drop_path=args.drop_path,
        out_channels=args.hidden_dim,
        out_feature_indexes=args.out_feature_indexes,
        projector_scale=args.projector_scale,
        use_cls_token=args.use_cls_token,
        hidden_dim=args.hidden_dim,
        position_embedding=args.position_embedding,
        freeze_encoder=args.freeze_encoder,
        layer_norm=args.layer_norm,
        target_shape=args.shape if hasattr(args, 'shape') else (args.resolution, args.resolution) if hasattr(args, 'resolution') else (640, 640),
        rms_norm=args.rms_norm,
        backbone_lora=args.backbone_lora,
        force_no_pretrain=args.force_no_pretrain,
        gradient_checkpointing=args.gradient_checkpointing,
        load_dinov2_weights=args.pretrain_weights is None,
        patch_size=args.patch_size,
        num_windows=args.num_windows,
        positional_encoding_size=args.positional_encoding_size,
    )
    if args.encoder_only:
        return backbone[0].encoder, None, None
    if args.backbone_only:
        return backbone, None, None

    args.num_feature_levels = len(args.projector_scale)
    transformer = build_transformer(args)

    model = LWDETR(
        backbone,
        transformer,
        num_classes=num_classes,
        num_queries=args.num_queries,
        aux_loss=args.aux_loss,
        group_detr=args.group_detr,
        two_stage=args.two_stage,
        lite_refpoint_refine=args.lite_refpoint_refine,
        bbox_reparam=args.bbox_reparam,
    )
    return model

def build_criterion_and_postprocessors(args):
    device = torch.device(args.device)
    matcher = build_matcher(args)
    weight_dict = {'loss_ce': args.cls_loss_coef, 'loss_bbox': args.bbox_loss_coef}
    weight_dict['loss_giou'] = args.giou_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()})
        if args.two_stage:
            aux_weight_dict.update({k + f'_enc': v for k, v in weight_dict.items()})
        weight_dict.update(aux_weight_dict)

    losses = ['labels', 'boxes', 'cardinality']

    try:
        sum_group_losses = args.sum_group_losses
    except:
        sum_group_losses = False
    criterion = SetCriterion(args.num_classes + 1, matcher=matcher, weight_dict=weight_dict,
                             focal_alpha=args.focal_alpha, losses=losses, 
                             group_detr=args.group_detr, sum_group_losses=sum_group_losses,
                             use_varifocal_loss = args.use_varifocal_loss,
                             use_position_supervised_loss=args.use_position_supervised_loss,
                             ia_bce_loss=args.ia_bce_loss)
    criterion.to(device)
    postprocessors = {'bbox': PostProcess(num_select=args.num_select)}

    return criterion, postprocessors