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""" Mixup and Cutmix
Papers:
mixup: Beyond Empirical Risk Minimization (https://arxiv.org/abs/1710.09412)
CutMix: Regularization Strategy to Train Strong Classifiers with Localizable Features (https://arxiv.org/abs/1905.04899)
Code Reference:
CutMix: https://github.com/clovaai/CutMix-PyTorch
Hacked together by / Copyright 2019, Ross Wightman
"""
import numpy as np
import torch
def one_hot(x, num_classes, on_value=1., off_value=0., device='cuda'):
x = x.long().view(-1, 1)
return torch.full((x.size()[0], num_classes), off_value, device=device).scatter_(1, x, on_value)
def mixup_target(target, num_classes, lam=1., smoothing=0.0, device='cuda'):
off_value = smoothing / num_classes
on_value = 1. - smoothing + off_value
y1 = one_hot(target, num_classes, on_value=on_value, off_value=off_value, device=device)
y2 = one_hot(target.flip(0), num_classes, on_value=on_value, off_value=off_value, device=device)
return y1 * lam + y2 * (1. - lam)
def rand_bbox(img_shape, lam, margin=0., count=None):
""" Standard CutMix bounding-box
Generates a random square bbox based on lambda value. This impl includes
support for enforcing a border margin as percent of bbox dimensions.
Args:
img_shape (tuple): Image shape as tuple
lam (float): Cutmix lambda value
margin (float): Percentage of bbox dimension to enforce as margin (reduce amount of box outside image)
count (int): Number of bbox to generate
"""
ratio = np.sqrt(1 - lam)
img_h, img_w = img_shape[-2:]
cut_h, cut_w = int(img_h * ratio), int(img_w * ratio)
margin_y, margin_x = int(margin * cut_h), int(margin * cut_w)
cy = np.random.randint(0 + margin_y, img_h - margin_y, size=count)
cx = np.random.randint(0 + margin_x, img_w - margin_x, size=count)
yl = np.clip(cy - cut_h // 2, 0, img_h)
yh = np.clip(cy + cut_h // 2, 0, img_h)
xl = np.clip(cx - cut_w // 2, 0, img_w)
xh = np.clip(cx + cut_w // 2, 0, img_w)
return yl, yh, xl, xh
def rand_bbox_minmax(img_shape, minmax, count=None):
""" Min-Max CutMix bounding-box
Inspired by Darknet cutmix impl, generates a random rectangular bbox
based on min/max percent values applied to each dimension of the input image.
Typical defaults for minmax are usually in the .2-.3 for min and .8-.9 range for max.
Args:
img_shape (tuple): Image shape as tuple
minmax (tuple or list): Min and max bbox ratios (as percent of image size)
count (int): Number of bbox to generate
"""
assert len(minmax) == 2
img_h, img_w = img_shape[-2:]
cut_h = np.random.randint(int(img_h * minmax[0]), int(img_h * minmax[1]), size=count)
cut_w = np.random.randint(int(img_w * minmax[0]), int(img_w * minmax[1]), size=count)
yl = np.random.randint(0, img_h - cut_h, size=count)
xl = np.random.randint(0, img_w - cut_w, size=count)
yu = yl + cut_h
xu = xl + cut_w
return yl, yu, xl, xu
def cutmix_bbox_and_lam(img_shape, lam, ratio_minmax=None, correct_lam=True, count=None):
""" Generate bbox and apply lambda correction.
"""
if ratio_minmax is not None:
yl, yu, xl, xu = rand_bbox_minmax(img_shape, ratio_minmax, count=count)
else:
yl, yu, xl, xu = rand_bbox(img_shape, lam, count=count)
if correct_lam or ratio_minmax is not None:
bbox_area = (yu - yl) * (xu - xl)
lam = 1. - bbox_area / float(img_shape[-2] * img_shape[-1])
return (yl, yu, xl, xu), lam
class Mixup:
""" Mixup/Cutmix that applies different params to each element or whole batch
Args:
mixup_alpha (float): mixup alpha value, mixup is active if > 0.
cutmix_alpha (float): cutmix alpha value, cutmix is active if > 0.
cutmix_minmax (List[float]): cutmix min/max image ratio, cutmix is active and uses this vs alpha if not None.
prob (float): probability of applying mixup or cutmix per batch or element
switch_prob (float): probability of switching to cutmix instead of mixup when both are active
mode (str): how to apply mixup/cutmix params (per 'batch', 'pair' (pair of elements), 'elem' (element)
correct_lam (bool): apply lambda correction when cutmix bbox clipped by image borders
label_smoothing (float): apply label smoothing to the mixed target tensor
num_classes (int): number of classes for target
"""
def __init__(self, mixup_alpha=1., cutmix_alpha=0., cutmix_minmax=None, prob=1.0, switch_prob=0.5,
mode='batch', correct_lam=True, label_smoothing=0.1, num_classes=1000):
self.mixup_alpha = mixup_alpha
self.cutmix_alpha = cutmix_alpha
self.cutmix_minmax = cutmix_minmax
if self.cutmix_minmax is not None:
assert len(self.cutmix_minmax) == 2
# force cutmix alpha == 1.0 when minmax active to keep logic simple & safe
self.cutmix_alpha = 1.0
self.mix_prob = prob
self.switch_prob = switch_prob
self.label_smoothing = label_smoothing
self.num_classes = num_classes
self.mode = mode
self.correct_lam = correct_lam # correct lambda based on clipped area for cutmix
self.mixup_enabled = True # set to false to disable mixing (intended tp be set by train loop)
def _params_per_elem(self, batch_size):
lam = np.ones(batch_size, dtype=np.float32)
use_cutmix = np.zeros(batch_size, dtype=np.bool)
if self.mixup_enabled:
if self.mixup_alpha > 0. and self.cutmix_alpha > 0.:
use_cutmix = np.random.rand(batch_size) < self.switch_prob
lam_mix = np.where(
use_cutmix,
np.random.beta(self.cutmix_alpha, self.cutmix_alpha, size=batch_size),
np.random.beta(self.mixup_alpha, self.mixup_alpha, size=batch_size))
elif self.mixup_alpha > 0.:
lam_mix = np.random.beta(self.mixup_alpha, self.mixup_alpha, size=batch_size)
elif self.cutmix_alpha > 0.:
use_cutmix = np.ones(batch_size, dtype=np.bool)
lam_mix = np.random.beta(self.cutmix_alpha, self.cutmix_alpha, size=batch_size)
else:
assert False, "One of mixup_alpha > 0., cutmix_alpha > 0., cutmix_minmax not None should be true."
lam = np.where(np.random.rand(batch_size) < self.mix_prob, lam_mix.astype(np.float32), lam)
return lam, use_cutmix
def _params_per_batch(self):
lam = 1.
use_cutmix = False
if self.mixup_enabled and np.random.rand() < self.mix_prob:
if self.mixup_alpha > 0. and self.cutmix_alpha > 0.:
use_cutmix = np.random.rand() < self.switch_prob
lam_mix = np.random.beta(self.cutmix_alpha, self.cutmix_alpha) if use_cutmix else \
np.random.beta(self.mixup_alpha, self.mixup_alpha)
elif self.mixup_alpha > 0.:
lam_mix = np.random.beta(self.mixup_alpha, self.mixup_alpha)
elif self.cutmix_alpha > 0.:
use_cutmix = True
lam_mix = np.random.beta(self.cutmix_alpha, self.cutmix_alpha)
else:
assert False, "One of mixup_alpha > 0., cutmix_alpha > 0., cutmix_minmax not None should be true."
lam = float(lam_mix)
return lam, use_cutmix
def _mix_elem(self, x):
batch_size = len(x)
lam_batch, use_cutmix = self._params_per_elem(batch_size)
x_orig = x.clone() # need to keep an unmodified original for mixing source
for i in range(batch_size):
j = batch_size - i - 1
lam = lam_batch[i]
if lam != 1.:
if use_cutmix[i]:
(yl, yh, xl, xh), lam = cutmix_bbox_and_lam(
x[i].shape, lam, ratio_minmax=self.cutmix_minmax, correct_lam=self.correct_lam)
x[i][:, yl:yh, xl:xh] = x_orig[j][:, yl:yh, xl:xh]
lam_batch[i] = lam
else:
x[i] = x[i] * lam + x_orig[j] * (1 - lam)
return torch.tensor(lam_batch, device=x.device, dtype=x.dtype).unsqueeze(1)
def _mix_pair(self, x):
batch_size = len(x)
lam_batch, use_cutmix = self._params_per_elem(batch_size // 2)
x_orig = x.clone() # need to keep an unmodified original for mixing source
for i in range(batch_size // 2):
j = batch_size - i - 1
lam = lam_batch[i]
if lam != 1.:
if use_cutmix[i]:
(yl, yh, xl, xh), lam = cutmix_bbox_and_lam(
x[i].shape, lam, ratio_minmax=self.cutmix_minmax, correct_lam=self.correct_lam)
x[i][:, yl:yh, xl:xh] = x_orig[j][:, yl:yh, xl:xh]
x[j][:, yl:yh, xl:xh] = x_orig[i][:, yl:yh, xl:xh]
lam_batch[i] = lam
else:
x[i] = x[i] * lam + x_orig[j] * (1 - lam)
x[j] = x[j] * lam + x_orig[i] * (1 - lam)
lam_batch = np.concatenate((lam_batch, lam_batch[::-1]))
return torch.tensor(lam_batch, device=x.device, dtype=x.dtype).unsqueeze(1)
def _mix_batch(self, x):
lam, use_cutmix = self._params_per_batch()
if lam == 1.:
return 1.
if use_cutmix:
(yl, yh, xl, xh), lam = cutmix_bbox_and_lam(
x.shape, lam, ratio_minmax=self.cutmix_minmax, correct_lam=self.correct_lam)
x[:, :, yl:yh, xl:xh] = x.flip(0)[:, :, yl:yh, xl:xh]
else:
x_flipped = x.flip(0).mul_(1. - lam)
x.mul_(lam).add_(x_flipped)
return lam
def __call__(self, x, target):
assert len(x) % 2 == 0, 'Batch size should be even when using this'
if self.mode == 'elem':
lam = self._mix_elem(x)
elif self.mode == 'pair':
lam = self._mix_pair(x)
else:
lam = self._mix_batch(x)
target = mixup_target(target, self.num_classes, lam, self.label_smoothing, x.device)
return x, target
class FastCollateMixup(Mixup):
""" Fast Collate w/ Mixup/Cutmix that applies different params to each element or whole batch
A Mixup impl that's performed while collating the batches.
"""
def _mix_elem_collate(self, output, batch, half=False):
batch_size = len(batch)
num_elem = batch_size // 2 if half else batch_size
assert len(output) == num_elem
lam_batch, use_cutmix = self._params_per_elem(num_elem)
for i in range(num_elem):
j = batch_size - i - 1
lam = lam_batch[i]
mixed = batch[i][0]
if lam != 1.:
if use_cutmix[i]:
if not half:
mixed = mixed.copy()
(yl, yh, xl, xh), lam = cutmix_bbox_and_lam(
output.shape, lam, ratio_minmax=self.cutmix_minmax, correct_lam=self.correct_lam)
mixed[:, yl:yh, xl:xh] = batch[j][0][:, yl:yh, xl:xh]
lam_batch[i] = lam
else:
mixed = mixed.astype(np.float32) * lam + batch[j][0].astype(np.float32) * (1 - lam)
np.rint(mixed, out=mixed)
output[i] += torch.from_numpy(mixed.astype(np.uint8))
if half:
lam_batch = np.concatenate((lam_batch, np.ones(num_elem)))
return torch.tensor(lam_batch).unsqueeze(1)
def _mix_pair_collate(self, output, batch):
batch_size = len(batch)
lam_batch, use_cutmix = self._params_per_elem(batch_size // 2)
for i in range(batch_size // 2):
j = batch_size - i - 1
lam = lam_batch[i]
mixed_i = batch[i][0]
mixed_j = batch[j][0]
assert 0 <= lam <= 1.0
if lam < 1.:
if use_cutmix[i]:
(yl, yh, xl, xh), lam = cutmix_bbox_and_lam(
output.shape, lam, ratio_minmax=self.cutmix_minmax, correct_lam=self.correct_lam)
patch_i = mixed_i[:, yl:yh, xl:xh].copy()
mixed_i[:, yl:yh, xl:xh] = mixed_j[:, yl:yh, xl:xh]
mixed_j[:, yl:yh, xl:xh] = patch_i
lam_batch[i] = lam
else:
mixed_temp = mixed_i.astype(np.float32) * lam + mixed_j.astype(np.float32) * (1 - lam)
mixed_j = mixed_j.astype(np.float32) * lam + mixed_i.astype(np.float32) * (1 - lam)
mixed_i = mixed_temp
np.rint(mixed_j, out=mixed_j)
np.rint(mixed_i, out=mixed_i)
output[i] += torch.from_numpy(mixed_i.astype(np.uint8))
output[j] += torch.from_numpy(mixed_j.astype(np.uint8))
lam_batch = np.concatenate((lam_batch, lam_batch[::-1]))
return torch.tensor(lam_batch).unsqueeze(1)
def _mix_batch_collate(self, output, batch):
batch_size = len(batch)
lam, use_cutmix = self._params_per_batch()
if use_cutmix:
(yl, yh, xl, xh), lam = cutmix_bbox_and_lam(
output.shape, lam, ratio_minmax=self.cutmix_minmax, correct_lam=self.correct_lam)
for i in range(batch_size):
j = batch_size - i - 1
mixed = batch[i][0]
if lam != 1.:
if use_cutmix:
mixed = mixed.copy() # don't want to modify the original while iterating
mixed[:, yl:yh, xl:xh] = batch[j][0][:, yl:yh, xl:xh]
else:
mixed = mixed.astype(np.float32) * lam + batch[j][0].astype(np.float32) * (1 - lam)
np.rint(mixed, out=mixed)
output[i] += torch.from_numpy(mixed.astype(np.uint8))
return lam
def __call__(self, batch, _=None):
batch_size = len(batch)
assert batch_size % 2 == 0, 'Batch size should be even when using this'
half = 'half' in self.mode
if half:
batch_size //= 2
output = torch.zeros((batch_size, *batch[0][0].shape), dtype=torch.uint8)
if self.mode == 'elem' or self.mode == 'half':
lam = self._mix_elem_collate(output, batch, half=half)
elif self.mode == 'pair':
lam = self._mix_pair_collate(output, batch)
else:
lam = self._mix_batch_collate(output, batch)
target = torch.tensor([b[1] for b in batch], dtype=torch.int64)
target = mixup_target(target, self.num_classes, lam, self.label_smoothing, device='cpu')
target = target[:batch_size]
return output, target