半监督学习之数据增强

一般选择的未标记图片及其伪标签不直接送入网络进行retraining ，在此之前，我们需要对未标记图片及其伪标签做相应的增强操作，以便网络能学习额外的特征并且缓解对噪音的过拟合。
常见的增强操作：

1:裁剪

直接裁剪或者填充为指定大小

2:翻转

上下翻转、左右翻转、旋转指定角度

3:标准化

transforms.Normalize()

4:滤波

PIL的ImageFilter模块介绍

5:resize（插值法填充）

最邻近（nearest）与双线性（bilinear）

6:cutout

cutout是2017年提出的一种数据增强方法，想法比较简单，即在训练时随机裁剪掉图像的一部分，也可以看作是一种类似dropout的正则化方法。

Improved Regularization of Convolutional Neural Networks with Cutout
paper: https://arxiv.org/pdf/1708.04552.pdf
code: https://github.com/uoguelph-mlrg/Cutout

将以上操作使用PIL库实现并封装，方便后续调用。

import numpy as np
from PIL import Image, ImageOps, ImageFilter
import random
import torch
from torchvision import transforms
import cv2

class DataAugmentations():
    def __init__(self):
        pass
    def crop(self,img, mask, size):
        # padding height or width if smaller than cropping size
        w, h = img.size
        padw = size - w if w < size else 0
        padh = size - h if h < size else 0
        img = ImageOps.expand(img, border=(0, 0, padw, padh), fill=0)
        mask = ImageOps.expand(mask, border=(0, 0, padw, padh), fill=255)

        # cropping
        w, h = img.size
        x = random.randint(0, w - size)
        y = random.randint(0, h - size)
        img = img.crop((x, y, x + size, y + size))
        mask = mask.crop((x, y, x + size, y + size))

        return img, mask


    def hflip(self,img, mask, p=0.5):
        if random.random() < p:
            ''' FLIP_LEFT_RIGHT = 0 左右翻转 FLIP_TOP_BOTTOM = 1 上下翻转 ROTATE_90 = 2 旋转 ROTATE_180 = 3 ROTATE_270 = 4 TRANSPOSE = 5 TRANSVERSE = 6 '''
            img = img.transpose(Image.FLIP_LEFT_RIGHT)
            mask = mask.transpose(Image.FLIP_LEFT_RIGHT)
        return img, mask


    def normalize(self,img, mask=None):
        """ :param img: PIL image :param mask: PIL image, corresponding mask :return: normalized torch tensor of image and mask """
        img = transforms.Compose([
            transforms.ToTensor(),
            transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225]),
        ])(img)
        if mask is not None:
            mask = torch.from_numpy(np.array(mask)).long()
            return img, mask
        return img


    def resize(self,img, mask, base_size, ratio_range):
        w, h = img.size
        long_side = random.randint(int(base_size * ratio_range[0]), int(base_size * ratio_range[1]))

        if h > w:
            oh = long_side
            ow = int(1.0 * w * long_side / h + 0.5)
        else:
            ow = long_side
            oh = int(1.0 * h * long_side / w + 0.5)

        img = img.resize((ow, oh), Image.BILINEAR)
        mask = mask.resize((ow, oh), Image.NEAREST)
        return img, mask


    def blur(self,img, p=0.5):
        if random.random() < p:
            sigma = np.random.uniform(0.1, 2.0)
            img = img.filter(ImageFilter.GaussianBlur(radius=sigma))
        return img


    def cutout(self,img, mask, p=0.5, size_min=0.02, size_max=0.4, ratio_1=0.3,
               ratio_2=1/0.3, value_min=0, value_max=255, pixel_level=True):
        if random.random() < p:
            img = np.array(img)
            mask = np.array(mask)

            img_h, img_w, img_c = img.shape

            while True:
                size = np.random.uniform(size_min, size_max) * img_h * img_w
                ratio = np.random.uniform(ratio_1, ratio_2)
                erase_w = int(np.sqrt(size / ratio))
                erase_h = int(np.sqrt(size * ratio))
                x = np.random.randint(0, img_w)
                y = np.random.randint(0, img_h)

                if x + erase_w <= img_w and y + erase_h <= img_h:
                    break

            if pixel_level:
                value = np.random.uniform(value_min, value_max, (erase_h, erase_w, img_c))
            else:
                value = np.random.uniform(value_min, value_max)

            img[y:y + erase_h, x:x + erase_w] = value
            mask[y:y + erase_h, x:x + erase_w] = 255

            img = Image.fromarray(img.astype(np.uint8))
            mask = Image.fromarray(mask.astype(np.uint8))

        return img, mask

if __name__=="__main__":
        SDA=DataAugmentations()
        img=Image.open("your path")
        mask=Image.open("your path")
        image1,mask1=SDA.hflip(img,mask)
        image1.show(title="刘亦菲")

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