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import torch | |
import torch.nn as nn | |
import torch.nn.functional as F | |
from ..general import xywh2xyxy | |
from ..loss import FocalLoss, smooth_BCE | |
from ..metrics import bbox_iou | |
from ..torch_utils import de_parallel | |
from .general import crop_mask | |
class ComputeLoss: | |
# Compute losses | |
def __init__(self, model, autobalance=False, overlap=False): | |
self.sort_obj_iou = False | |
self.overlap = overlap | |
device = next(model.parameters()).device # get model device | |
h = model.hyp # hyperparameters | |
self.device = device | |
# Define criteria | |
BCEcls = nn.BCEWithLogitsLoss( | |
pos_weight=torch.tensor([h["cls_pw"]], device=device) | |
) | |
BCEobj = nn.BCEWithLogitsLoss( | |
pos_weight=torch.tensor([h["obj_pw"]], device=device) | |
) | |
# Class label smoothing https://arxiv.org/pdf/1902.04103.pdf eqn 3 | |
self.cp, self.cn = smooth_BCE( | |
eps=h.get("label_smoothing", 0.0) | |
) # positive, negative BCE targets | |
# Focal loss | |
g = h["fl_gamma"] # focal loss gamma | |
if g > 0: | |
BCEcls, BCEobj = FocalLoss(BCEcls, g), FocalLoss(BCEobj, g) | |
m = de_parallel(model).model[-1] # Detect() module | |
self.balance = {3: [4.0, 1.0, 0.4]}.get( | |
m.nl, [4.0, 1.0, 0.25, 0.06, 0.02] | |
) # P3-P7 | |
self.ssi = ( | |
list(m.stride).index(16) if autobalance else 0 | |
) # stride 16 index | |
self.BCEcls, self.BCEobj, self.gr, self.hyp, self.autobalance = ( | |
BCEcls, | |
BCEobj, | |
1.0, | |
h, | |
autobalance, | |
) | |
self.na = m.na # number of anchors | |
self.nc = m.nc # number of classes | |
self.nl = m.nl # number of layers | |
self.nm = m.nm # number of masks | |
self.anchors = m.anchors | |
self.device = device | |
def __call__(self, preds, targets, masks): # predictions, targets, model | |
p, proto = preds | |
( | |
bs, | |
nm, | |
mask_h, | |
mask_w, | |
) = proto.shape # batch size, number of masks, mask height, mask width | |
lcls = torch.zeros(1, device=self.device) | |
lbox = torch.zeros(1, device=self.device) | |
lobj = torch.zeros(1, device=self.device) | |
lseg = torch.zeros(1, device=self.device) | |
tcls, tbox, indices, anchors, tidxs, xywhn = self.build_targets( | |
p, targets | |
) # targets | |
# Losses | |
for i, pi in enumerate(p): # layer index, layer predictions | |
b, a, gj, gi = indices[i] # image, anchor, gridy, gridx | |
tobj = torch.zeros( | |
pi.shape[:4], dtype=pi.dtype, device=self.device | |
) # target obj | |
n = b.shape[0] # number of targets | |
if n: | |
pxy, pwh, _, pcls, pmask = pi[b, a, gj, gi].split( | |
(2, 2, 1, self.nc, nm), 1 | |
) # subset of predictions | |
# Box regression | |
pxy = pxy.sigmoid() * 2 - 0.5 | |
pwh = (pwh.sigmoid() * 2) ** 2 * anchors[i] | |
pbox = torch.cat((pxy, pwh), 1) # predicted box | |
iou = bbox_iou( | |
pbox, tbox[i], CIoU=True | |
).squeeze() # iou(prediction, target) | |
lbox += (1.0 - iou).mean() # iou loss | |
# Objectness | |
iou = iou.detach().clamp(0).type(tobj.dtype) | |
if self.sort_obj_iou: | |
j = iou.argsort() | |
b, a, gj, gi, iou = b[j], a[j], gj[j], gi[j], iou[j] | |
if self.gr < 1: | |
iou = (1.0 - self.gr) + self.gr * iou | |
tobj[b, a, gj, gi] = iou # iou ratio | |
# Classification | |
if self.nc > 1: # cls loss (only if multiple classes) | |
t = torch.full_like( | |
pcls, self.cn, device=self.device | |
) # targets | |
t[range(n), tcls[i]] = self.cp | |
lcls += self.BCEcls(pcls, t) # BCE | |
# Mask regression | |
if tuple(masks.shape[-2:]) != (mask_h, mask_w): # downsample | |
masks = F.interpolate( | |
masks[None], (mask_h, mask_w), mode="nearest" | |
)[0] | |
marea = xywhn[i][:, 2:].prod( | |
1 | |
) # mask width, height normalized | |
mxyxy = xywh2xyxy( | |
xywhn[i] | |
* torch.tensor( | |
[mask_w, mask_h, mask_w, mask_h], device=self.device | |
) | |
) | |
for bi in b.unique(): | |
j = b == bi # matching index | |
if self.overlap: | |
mask_gti = torch.where( | |
masks[bi][None] == tidxs[i][j].view(-1, 1, 1), | |
1.0, | |
0.0, | |
) | |
else: | |
mask_gti = masks[tidxs[i]][j] | |
lseg += self.single_mask_loss( | |
mask_gti, pmask[j], proto[bi], mxyxy[j], marea[j] | |
) | |
obji = self.BCEobj(pi[..., 4], tobj) | |
lobj += obji * self.balance[i] # obj loss | |
if self.autobalance: | |
self.balance[i] = ( | |
self.balance[i] * 0.9999 + 0.0001 / obji.detach().item() | |
) | |
if self.autobalance: | |
self.balance = [x / self.balance[self.ssi] for x in self.balance] | |
lbox *= self.hyp["box"] | |
lobj *= self.hyp["obj"] | |
lcls *= self.hyp["cls"] | |
lseg *= self.hyp["box"] / bs | |
loss = lbox + lobj + lcls + lseg | |
return loss * bs, torch.cat((lbox, lseg, lobj, lcls)).detach() | |
def single_mask_loss(self, gt_mask, pred, proto, xyxy, area): | |
# Mask loss for one image | |
pred_mask = (pred @ proto.view(self.nm, -1)).view( | |
-1, *proto.shape[1:] | |
) # (n,32) @ (32,80,80) -> (n,80,80) | |
loss = F.binary_cross_entropy_with_logits( | |
pred_mask, gt_mask, reduction="none" | |
) | |
return (crop_mask(loss, xyxy).mean(dim=(1, 2)) / area).mean() | |
def build_targets(self, p, targets): | |
# Build targets for compute_loss(), input targets(image,class,x,y,w,h) | |
na, nt = self.na, targets.shape[0] # number of anchors, targets | |
tcls, tbox, indices, anch, tidxs, xywhn = [], [], [], [], [], [] | |
gain = torch.ones( | |
8, device=self.device | |
) # normalized to gridspace gain | |
ai = ( | |
torch.arange(na, device=self.device) | |
.float() | |
.view(na, 1) | |
.repeat(1, nt) | |
) # same as .repeat_interleave(nt) | |
if self.overlap: | |
batch = p[0].shape[0] | |
ti = [] | |
for i in range(batch): | |
num = ( | |
targets[:, 0] == i | |
).sum() # find number of targets of each image | |
ti.append( | |
torch.arange(num, device=self.device) | |
.float() | |
.view(1, num) | |
.repeat(na, 1) | |
+ 1 | |
) # (na, num) | |
ti = torch.cat(ti, 1) # (na, nt) | |
else: | |
ti = ( | |
torch.arange(nt, device=self.device) | |
.float() | |
.view(1, nt) | |
.repeat(na, 1) | |
) | |
targets = torch.cat( | |
(targets.repeat(na, 1, 1), ai[..., None], ti[..., None]), 2 | |
) # append anchor indices | |
g = 0.5 # bias | |
off = ( | |
torch.tensor( | |
[ | |
[0, 0], | |
[1, 0], | |
[0, 1], | |
[-1, 0], | |
[0, -1], # j,k,l,m | |
# [1, 1], [1, -1], [-1, 1], [-1, -1], # jk,jm,lk,lm | |
], | |
device=self.device, | |
).float() | |
* g | |
) # offsets | |
for i in range(self.nl): | |
anchors, shape = self.anchors[i], p[i].shape | |
gain[2:6] = torch.tensor(shape)[[3, 2, 3, 2]] # xyxy gain | |
# Match targets to anchors | |
t = targets * gain # shape(3,n,7) | |
if nt: | |
# Matches | |
r = t[..., 4:6] / anchors[:, None] # wh ratio | |
j = ( | |
torch.max(r, 1 / r).max(2)[0] < self.hyp["anchor_t"] | |
) # compare | |
# j = wh_iou(anchors, t[:, 4:6]) > model.hyp['iou_t'] # iou(3,n)=wh_iou(anchors(3,2), gwh(n,2)) | |
t = t[j] # filter | |
# Offsets | |
gxy = t[:, 2:4] # grid xy | |
gxi = gain[[2, 3]] - gxy # inverse | |
j, k = ((gxy % 1 < g) & (gxy > 1)).T | |
l, m = ((gxi % 1 < g) & (gxi > 1)).T | |
j = torch.stack((torch.ones_like(j), j, k, l, m)) | |
t = t.repeat((5, 1, 1))[j] | |
offsets = (torch.zeros_like(gxy)[None] + off[:, None])[j] | |
else: | |
t = targets[0] | |
offsets = 0 | |
# Define | |
bc, gxy, gwh, at = t.chunk( | |
4, 1 | |
) # (image, class), grid xy, grid wh, anchors | |
(a, tidx), (b, c) = ( | |
at.long().T, | |
bc.long().T, | |
) # anchors, image, class | |
gij = (gxy - offsets).long() | |
gi, gj = gij.T # grid indices | |
# Append | |
indices.append( | |
(b, a, gj.clamp_(0, shape[2] - 1), gi.clamp_(0, shape[3] - 1)) | |
) # image, anchor, grid | |
tbox.append(torch.cat((gxy - gij, gwh), 1)) # box | |
anch.append(anchors[a]) # anchors | |
tcls.append(c) # class | |
tidxs.append(tidx) | |
xywhn.append( | |
torch.cat((gxy, gwh), 1) / gain[2:6] | |
) # xywh normalized | |
return tcls, tbox, indices, anch, tidxs, xywhn | |