1. torchvision.transforms

在CV任务中，可以用此对图像进行预处理，数据增强等操作

1.1 Transforms on Image

import torchvision.transforms as transforms
from PIL import Image

img = Image.open('lena.png')
img = img.convert("RGB")
img

width, height = img.size
print(width, height)

132 193

1.1.1 transforms.Resize

把给定的图片resize到给定的size

size = (100, 100)
transform = transforms.Resize(size=size)
resize_img = transform(img)
resize_img

1.1.2 transforms.CenterCrop

在图片的中心区域进行裁剪

size = (100, 100)
transform = transforms.CenterCrop(size=size)
centercrop_img = transform(img)
centercrop_img

1.1.3 transforms.RandomCrop

在图片上随机一个位置进行裁剪

size = (100, 100)
transform = transforms.RandomCrop(size=size)
randomcrop_img = transform(img)
randomcrop_img

1.1.4 transforms.RandomHorizontalFlip§

以概率为p水平翻转给定的图像

transform = transforms.RandomHorizontalFlip(p=0.5)
rpf_img = transform(img)
rpf_img

1.1.5 transforms.RandomVerticalFlip§

以概率为p垂直翻转给定的图像

transform = transforms.RandomVerticalFlip(p=0.5)
rvf_img = transform(img)
rvf_img

1.1.6 transforms.ColorJitter

随机修改图片的亮度、对比度和饱和度，常用来进行数据增强

brightness = (1, 10)
contrast = (1, 10)
saturation = (1, 10)
hue = (0.2, 0.4)
transform = transforms.ColorJitter(brightness, contrast, saturation, hue)
colorjitter_img = transform(img)
colorjitter_img

1.1.7 transforms.Grayscale

将图像转换为灰度图像

transform = transforms.Grayscale()
gary_img = transform(img)
gary_img

1.1.8 transforms.RandomGrayscale

以概率p将图像转换为灰度图像

transform = transforms.RandomGrayscale(p=0.5)
rg_img = transform(img)
rg_img

1.2 transforms on Tensor

1.2.1 transforms.ToTensor()

将Image转换为Tensor

transform = transforms.ToTensor()
tensor_img = transform(img)
tensor_img

tensor([[[0.7176, 0.7294, 0.7255,  ..., 0.6627, 0.6549, 0.6627],
         [0.7137, 0.7176, 0.7176,  ..., 0.6510, 0.6510, 0.6549],
         [0.7137, 0.7176, 0.7137,  ..., 0.6392, 0.6431, 0.6353],
         ...,
         [0.9922, 1.0000, 0.9725,  ..., 0.6863, 0.6902, 0.7059],
         [1.0000, 1.0000, 0.9961,  ..., 0.6745, 0.6824, 0.6902],
         [1.0000, 0.9961, 0.9882,  ..., 0.6745, 0.6745, 0.6863]],

        [[0.3843, 0.3922, 0.3922,  ..., 0.3529, 0.3451, 0.3529],
         [0.3765, 0.3804, 0.3804,  ..., 0.3412, 0.3412, 0.3412],
         [0.3765, 0.3804, 0.3804,  ..., 0.3294, 0.3412, 0.3333],
         ...,
         [0.8745, 0.8941, 0.8863,  ..., 0.3294, 0.3490, 0.3647],
         [0.9098, 0.9176, 0.9176,  ..., 0.3216, 0.3373, 0.3490],
         [0.9294, 0.9255, 0.9255,  ..., 0.3216, 0.3294, 0.3412]],

        [[0.2745, 0.2863, 0.2784,  ..., 0.2353, 0.2235, 0.2353],
         [0.2784, 0.2745, 0.2745,  ..., 0.2353, 0.2353, 0.2314],
         [0.2784, 0.2745, 0.2706,  ..., 0.2275, 0.2392, 0.2353],
         ...,
         [0.8706, 0.8824, 0.8627,  ..., 0.2510, 0.2706, 0.2863],
         [0.9216, 0.9176, 0.9059,  ..., 0.2392, 0.2588, 0.2706],
         [0.9451, 0.9333, 0.9255,  ..., 0.2392, 0.2510, 0.2588]]])

1.2.2 transforms.Normalize

input[channel] = (input[channel] - mean[channel]) / std[channel]

transform = transforms.Normalize(mean=(0.5, 0.5, 0.5), std=(0.5, 0.5, 0.5))
img_normal = transform(tensor_img)
img_normal

tensor([[[ 0.4353,  0.4588,  0.4510,  ...,  0.3255,  0.3098,  0.3255],
         [ 0.4275,  0.4353,  0.4353,  ...,  0.3020,  0.3020,  0.3098],
         [ 0.4275,  0.4353,  0.4275,  ...,  0.2784,  0.2863,  0.2706],
         ...,
         [ 0.9843,  1.0000,  0.9451,  ...,  0.3725,  0.3804,  0.4118],
         [ 1.0000,  1.0000,  0.9922,  ...,  0.3490,  0.3647,  0.3804],
         [ 1.0000,  0.9922,  0.9765,  ...,  0.3490,  0.3490,  0.3725]],

        [[-0.2314, -0.2157, -0.2157,  ..., -0.2941, -0.3098, -0.2941],
         [-0.2471, -0.2392, -0.2392,  ..., -0.3176, -0.3176, -0.3176],
         [-0.2471, -0.2392, -0.2392,  ..., -0.3412, -0.3176, -0.3333],
         ...,
         [ 0.7490,  0.7882,  0.7725,  ..., -0.3412, -0.3020, -0.2706],
         [ 0.8196,  0.8353,  0.8353,  ..., -0.3569, -0.3255, -0.3020],
         [ 0.8588,  0.8510,  0.8510,  ..., -0.3569, -0.3412, -0.3176]],

        [[-0.4510, -0.4275, -0.4431,  ..., -0.5294, -0.5529, -0.5294],
         [-0.4431, -0.4510, -0.4510,  ..., -0.5294, -0.5294, -0.5373],
         [-0.4431, -0.4510, -0.4588,  ..., -0.5451, -0.5216, -0.5294],
         ...,
         [ 0.7412,  0.7647,  0.7255,  ..., -0.4980, -0.4588, -0.4275],
         [ 0.8431,  0.8353,  0.8118,  ..., -0.5216, -0.4824, -0.4588],
         [ 0.8902,  0.8667,  0.8510,  ..., -0.5216, -0.4980, -0.4824]]])

1.2.3 transforms.Compose

将多个变换组合在一起

img = Image.open('lena.png')
img = img.convert('RGB')

transform = transforms.Compose([
    transforms.Resize(100),
    transforms.RandomHorizontalFlip(),
    transforms.CenterCrop(64),
    transforms.ToTensor(),
    transforms.Normalize((.5, .5, .5), (.5, .5, .5))
])

img_compose = transform(img)
img_compose.size()

torch.Size([3, 64, 64])

2. torchvision.datasets

用来进行数据加载的，下面以CIFAR-10数据集为例，其中transform表示对数据进行预处理，对应着上面所讲

import torchvision

trainset = torchvision.datasets.CIFAR10(
    root='./dataset',  # 数据集下载的地方
    train=True,   # True表示创建训练集；False表示创建测试集
    download=True, # 如果为true，则从Internet下载数据集。如果已下载数据集，则不会再次下载
    transform=None  # 表示是否对数据进行预处理，None表示不做任何处理
)

3. torch.utils.data.DataLoader

import torch
from torch.utils.data.sampler import SubsetRandomSampler

trainloader = torch.utils.data.DataLoader(
    dataset=trainset,  # 加载torch.utils.data.Dataset对象数据或者是torchvision.datasets中的数据
    batch_size=1, # 每个batch所含样本的大小
    shuffle=False, # 是否对数据进行打乱
    sampler=SubsetRandomSampler(indices=), # 按指定下标进行取样，如果此参数被指定，shuffle参数必须为False
    drop_last=False, # 当整个数据集不能整除batch_size，False表示最后一个batch的大小会变小，True表示直接丢弃最后一个batch
    num_workers=0 # 表示加载的时候子进程数
)

4. torch.utils.data.Dataset

from torch.utils.data.dataset import Dataset


# 基本框架
class CustomDataset(Dataset):
    def __init__(self):
    	"""
    	一些初始化过程写在这里
    	"""
        # TODO
        # 1. Initialize file paths or a list of file names. 
        pass
    def __getitem__(self, index):
    	"""
    	返回数据和标签，可以这样显示调用：
    	img, label = MyCustomDataset.__getitem__(index)
    	"""
        # TODO
        # 1. Read one data from file (e.g. using numpy.fromfile, PIL.Image.open).
        # 2. Preprocess the data (e.g. torchvision.Transform).
        # 3. Return a data pair (e.g. image and label).
        pass
    def __len__(self):
    	"""
    	返回所有数据的数量
    	"""
        # You should change 9 to the total size of your dataset.
        return 9 # e.g. 9 is size of dataset

目前我们有一个关于图像分类的问题，数据结构如下：

其中一个是训练文件夹，一个测试文件夹，分类的类别数为6个，其中每个文件夹包含很多图片

如何构建Custom Dataset

1. 分别为训练集和测试集建立两个DataFrame文件，其中DataFrame文件有两列，一列是图片的名字，令一列为标签

Images	Labels
0.jpg	0
99.jpg	5

2. 构建Custom Dataset

class INTELDataset(Dataset):
    def __init__(self, img_data,img_path,transform=None):
        self.img_path = img_path    # 数据路径
        self.transform = transform
        self.img_data = img_data  # DaraFrame
        
   
    
    def __getitem__(self, index):
        img_name = os.path.join(self.img_path,self.img_data.loc[index, 'labels'],
                                self.img_data.loc[index, 'Images'])  # 图片路径
        image = Image.open(img_name)  # 获得图片
        image = image.convert('RGB')
        label = torch.tensor(self.img_data.loc[index, 'labels'])  # 获得标签
        if self.transform is not None:
            image = self.transform(image)
        return image, label

    
    
    def __len__(self):
        return len(self.img_data)  # 数据大小