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分割任务对 image 做（某些）transform 时，要对 label（segmentation mask）也做对应的 transform，如 Resize、RandomRotation 等。如果对 image、label 分别用 transform 处理一遍，则涉及随机操作的可能不一致，如 RandomRotation 将 image 转了 a 度、却将 label 转了 b 度。

MONAI 有个 ArrayDataset 实现了这功能，思路是每次 transform 前都重置一次 random seed 先。对 monai 订制 transform 的方法不熟，torchvision.transforms 的订制接口比较简单，考虑基于 pytorch 实现。要改两个东西：

• 扩展 torchvison.transforms.Compose，使之支持多个输入（image、label）；
• 一个 wrapper，扩展 transform，使之支持多输入。

思路也是重置 random seed，参考 [1-4]。

Code

import random, os
import numpy as np
import torchdef seed_everything(seed=42):random.seed(seed)os.environ['PYTHONHASHSEED'] = str(seed)np.random.seed(seed)torch.manual_seed(seed)torch.cuda.manual_seed(seed)torch.backends.cudnn.deterministic = Truetorch.backends.cudnn.benchmark = Truedef to_multi(trfm):"""wrap a transform to extend to multiple input with synchronised random seedInput:trfm: transformation function/object (custom or from torchvision.transforms)Output:_multi_transform: function"""# numpy.random.seed range error:#   ValueError: Seed must be between 0 and 2**32 - 1min_seed = 0 # - 0x8000_0000_0000_0000max_seed = min(2**32 - 1, 0xffff_ffff_ffff_ffff)def _multi_transform(*images):"""images: [C, H, W]"""if len(images) == 1:return trfm(images[0])_seed = random.randint(min_seed, max_seed)res = []for img in images:seed_everything(_seed)res.append(trfm(img))return tuple(res)return _multi_transformclass MultiCompose:"""Extension of torchvision.transforms.Compose that accepts multiple input.Usage is the same as torchvision.transforms.Compose. This class will wrap inputtransforms with `to_multi` to support simultaneous multiple transformation.This can be useful when simultaneously transforming images & segmentation masks."""def __init__(self, transforms):"""transforms should be wrapped by `to_multi`"""self.transforms = [to_multi(t) for t in transforms]def __call__(self, *images):for t in self.transforms:images = t(*images)return images

test

测试一致性，用到预处理过的 verse’19 数据集、一些工具函数、一个订制 transform：

• verse’19 数据集及预处理见 iTomxy/data/verse；
• digit_sort_key：数据文件排序用；
• get_palette、color_seg、blend_seg：可视化用；
• MyDataset：看其中 __getitem__ 的 transform 用法，即同时传入 image 和 label；
• ResizeZoomPad：一个订制的 transform；

import os, os.path as osp, random
from glob import glob
import numpy as np
from PIL import Image
import torch
import torchvision.transforms as transforms
import torchvision.transforms.functional as Fdef digit_sort_key(s, num_pattern=re.compile('([0-9]+)')):"""natural sort，数据排序用"""return [int(text) for text in num_pattern.split(s) if text.isdigit()]def get_palette(n_classes, pil_format=True):"""创建调色盘，可视化用"""n = n_classespalette = [0] * (n * 3)for j in range(0, n):lab = jpalette[j * 3 + 0] = 0palette[j * 3 + 1] = 0palette[j * 3 + 2] = 0i = 0while lab:palette[j * 3 + 0] |= (((lab >> 0) & 1) << (7 - i))palette[j * 3 + 1] |= (((lab >> 1) & 1) << (7 - i))palette[j * 3 + 2] |= (((lab >> 2) & 1) << (7 - i))i += 1lab >>= 3if pil_format:return paletteres = []for i in range(0, len(palette), 3):res.append(tuple(palette[i: i+3]))return resdef color_seg(label, n_classes=0):"""segmentation mask 上色，可视化用"""if n_classes < 1:n_classes = math.ceil(np.max(label)) + 1label_rgb = Image.fromarray(label.astype(np.int32)).convert("L")label_rgb.putpalette(get_palette(n_classes))return label_rgb.convert("RGB")def blend_seg(image, label, n_classes=0, alpha=0.7, rescale=False, transparent_bg=True, save_file=""):"""融合 image 和其 segmentation mask，可视化用"""if rescale:denom = image.max() - image.min()if 0 != denom:image = (image - image.min()) / denom * 255image = np.clip(image, 0, 255).astype(np.uint8)img_pil = Image.fromarray(image).convert("RGB")lab_pil = color_seg(label, n_classes)blended_image = Image.blend(img_pil, lab_pil, alpha)if transparent_bg:blended_image = Image.fromarray(np.where((0 == label)[:, :, np.newaxis],np.asarray(img_pil),np.asarray(blended_image)))if save_file:blended_image.save(save_file)return blended_imageclass MyDataset(torch.utils.data.Dataset):"""订制 dataset，看 __getitem__ 处 transform 的调法"""def __init__(self, image_list, label_list, transform=None):assert len(image_list) == len(label_list)self.image_list = image_listself.label_list = label_listself.transform = transformdef __len__(self):return len(self.image_list)def __getitem__(self, index):img = np.load(self.image_list[index]) # [h, w]lab = np.load(self.label_list[index])img = torch.from_numpy(img).unsqueeze(0).float() # -> [c=1, h, w]lab = torch.from_numpy(lab).unsqueeze(0).int()if self.transform is not None:img, lab = self.transform(img, lab) # 同时传入 image、labelreturn img, labclass ResizeZoomPad:"""订制 resize"""def __init__(self, size, interpolation="bilinear"):if isinstance(size, int):assert size > 0self.size = [size, size]elif isinstance(size, (tuple, list)):assert len(size) == 2 and size[0] > 0 and size[1] > 0self.size = sizeif isinstance(interpolation, str):assert interpolation.lower() in {"nearest", "bilinear", "bicubic", "box", "hamming", "lanczos"}interpolation = {"nearest": F.InterpolationMode.NEAREST,"bilinear": F.InterpolationMode.BILINEAR,"bicubic": F.InterpolationMode.BICUBIC,"box": F.InterpolationMode.BOX,"hamming": F.InterpolationMode.HAMMING,"lanczos": F.InterpolationMode.LANCZOS}[interpolation.lower()]self.interpolation = interpolationdef __call__(self, image):"""image: [C, H, W]"""scale_h, scale_w = float(self.size[0]) / image.size(1), float(self.size[1]) / image.size(2)scale = min(scale_h, scale_w)tmp_size = [ # clipping to ensure sizemin(int(image.size(1) * scale), self.size[0]),min(int(image.size(2) * scale), self.size[1])]image = F.resize(image, tmp_size, self.interpolation)assert image.size(1) <= self.size[0] and image.size(2) <= self.size[1]pad_h, pad_w = self.size[0] - image.size(1), self.size[1] - image.size(2)if pad_h > 0 or pad_w > 0:pad_left, pad_right = pad_w // 2, (pad_w + 1) // 2pad_top, pad_bottom = pad_h // 2, (pad_h + 1) // 2image = F.pad(image, (pad_left, pad_top, pad_right, pad_bottom))return image# 读数据文件
data_path = os.path.expanduser("~/data/verse/processed-verse19-npy-horizontal")
train_images, train_labels, val_images, val_labels = [], [], [], []
for d in os.listdir(osp.join(data_path, "training")):if d.endswith("_ct"):img_p = osp.join(data_path, "training", d)lab_p = osp.join(data_path, "training", d[:-3]+"_seg-vert_msk")assert osp.isdir(lab_p)train_labels.extend(glob(os.path.join(lab_p, "*.npy")))train_images.extend(glob(os.path.join(img_p, "*.npy")))
for d in os.listdir(osp.join(data_path, "validation")):if d.endswith("_ct"):img_p = osp.join(data_path, "validation", d)lab_p = osp.join(data_path, "validation", d[:-3]+"_seg-vert_msk")assert osp.isdir(lab_p)val_labels.extend(glob(os.path.join(lab_p, "*.npy")))val_images.extend(glob(os.path.join(img_p, "*.npy")))# 数据文件名排序
train_images = sorted(train_images, key=lambda f: digit_sort_key(os.path.basename(f)))
train_labels = sorted(train_labels, key=lambda f: digit_sort_key(os.path.basename(f)))
val_images = sorted(val_images, key=lambda f: digit_sort_key(os.path.basename(f)))
val_labels = sorted(val_labels, key=lambda f: digit_sort_key(os.path.basename(f)))# transform
# 用 MultiCompose，其内部调用 to_multi 将 transforms wrap 成支持多输入的
train_trans = MultiCompose([ResizeZoomPad((224, 256)),transforms.RandomRotation(30),
])# 测试：读数据，可试化 image 和 label
check_ds = MyDataset(train_images, train_labels, train_trans)
check_loader = torch.utils.data.DataLoader(check_ds, batch_size=10, shuffle=True)
for images, labels in check_loader:print(images.size(), labels.size())for i in range(images.size(0)):# print(i, end='\r')img = images[i][0].numpy()lab = labels[i][0].numpy()print(np.unique(lab))seg_img = blend_seg(img, lab)img = (255 * (img - img.min()) / (img.max() - img.min())).astype(np.uint8)img = np.asarray(Image.fromarray(img).convert("RGB"))lab = np.asarray(color_seg(lab))comb = np.concatenate([img, lab, seg_img], axis=1)Image.fromarray(comb).save(f"test-dataset-{i}.png")break

效果：

可见，image 和 label 转了同一个随机角度。

Limits

有些 augmentations 是只对 image 做而不对 label 做的，如 ColorJitter，这里没有考虑怎么处理。

References

1. How to Set Random Seeds in PyTorch and Tensorflow
2. ihoromi4/seed_everything.py
3. Reproducibility
4. What is the max seed you can set up?