目录

Transeforms的使用

常见的transforms

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Transeforms的使用

torchvision中的transeforms，主要是对图像进行变换（预处理）。from torchvision import transforms

transeforms中常用的就是以下几种方法：（Alt+7可唤出左侧的Structure结构）
“Compose”, “ToTensor”, “PILToTensor”, “ConvertImageDtype”, “ToPILImage”, “Normalize”, “Resize”, “Scale”,“CenterCrop”
 

Compose: Composes several transforms together. Args:list of transforms to compose.将几个变换组合在一起。参数：[Transform对象列表]，例如transforms.Compose([transforms.CenterCrop(10),transforms.ToTensor(),…])

ToTensor: Convert a PIL Image or numpy.ndarray to tensor.

ToPILImage: Convert a tensor or an ndarray to PIL Image.

Normalize(torch.nn.Module): Normalize a tensor image with mean and standard deviation.This transform does not support PIL Image.用平均值和标准偏差归一化张量图像。此转换不支持PIL图像。（为n个维度给定mean:(mean[1],…,mean[n])和std:(std[1],…,std[n])，此转换将对每个channel进行归一化）

Resize(torch.nn.Module): Resize the input image (PIL Image or Tensor) to the given size.Return PIL Image or Tensor: Rescaled image.将输入的图像(PIL Image or Tensor)的大小缩放到指定的size尺寸。size (sequence or int)，当是sequence时则调整到指定的(h, w)；当是int时，就将原图的min(h,w)调整到size大小，然后另一条边进行等比例缩放。

RandomCrop(torch.nn.Module): Crop the given image (PIL Image or Tensor) at a random location.在随机位置裁剪给定的size大小的图像（size的输入要求跟Resize一样）。

用ToTensor()将PIL Image转为tensor

也可以用 ToTensor() 将 numpy.ndarray 转为tensor（用opencv读入的数据类型是numpy.ndarray）

import numpy as np
from torchvision import transforms
from PIL import Imageimage_path = 'hymenoptera_data/train/ants/0013035.jpg'
image = Image.open(image_path)# 1.transforms该如何使用(python)
tensor_trans = transforms.ToTensor()	# ToTensor()中不带参数
tensor_img = tensor_trans(image)		# 不能直接写成transforms.ToTensor(image)print(np.array(image).shape)	# (512, 768, 3)
print(tensor_img.shape)			# torch.Size([3, 512, 768])，通道数变到第0维了

ToTensor与Tensorboard配合使用

import numpy as np
from torch.utils.tensorboard import SummaryWriter
from torchvision import transforms
from PIL import Imageimage_path = 'hymenoptera_data/train/ants/0013035.jpg'
image = Image.open(image_path)# 1.transforms该如何使用(python)
tensor_trans = transforms.ToTensor()
tensor_img = tensor_trans(image)print(np.array(image).shape)
print(tensor_img.shape)# 写入tensorboard
writer = SummaryWriter('logs')
writer.add_image('tag', tensor_img, 1)
writer.close()

常见的transforms

图像的数据类型在不同场景往往不同，很容易出错，需要转换为特定格式才能使用！

• __call__()方法的作用：把一个类的实例化对象变成了可调用对象。调用该实例对象就是执行__call__()方法中的代码。
• 可以通过内置函数callable来判断是否是可调用对象。例如判断p是否为可调用对象：print(callable(p))返回 True 或 False。

  class Person:def __call__(self, name):print('__call__' + ' Hello ' + name)def hello(self, name):print('hello ' + name)person = Person()               # 实例化一个对象person
  person('zhangsan')              # 像调用函数一样调用person对象
  person.__call__('zhangshan_2')  # 也可像调用类函数调用
  person.hello('wangwu')          # 调用类函数person# __call__ Hello zhangsan
  # __call__ Hello zhangshan_2
  # hello wangwu
  

  from torch.utils.tensorboard import SummaryWriter
  from torchvision import transforms
  from PIL import Imageimage_path = 'hymenoptera_data/train/ants/0013035.jpg'
  image = Image.open(image_path)writer = SummaryWriter('logs')# 1.Totensor
  trans_totensor = transforms.ToTensor()
  img_tensor = trans_totensor(image)
  writer.add_image('ToTensor', img_tensor)  # 这里只传入了tag和image_tensor，没有写入第3个参数global_step，则会默认是第0步# 2.Normalize 可以改变色调
  trans_norm = transforms.Normalize([0.5, 0.5, 0.5], [0.5, 0.5, 0.5])
  img_norm = trans_norm(img_tensor)
  writer.add_image('Normalize', img_norm)trans_norm = transforms.Normalize([1, 3, 5], [3, 2, 1])
  img_norm_2 = trans_norm(img_tensor)
  writer.add_image('Normalize', img_norm_2, 1)trans_norm = transforms.Normalize([2, 0.5, 3], [5, 2.6, 1.5])
  img_norm_3 = trans_norm(img_tensor)
  writer.add_image('Normalize', img_norm_3, 2)# 3.Resize 将PIL或者tensor缩放为指定大小然后输出PIL或者tensor
  w, h = image.size   # PIL.Image的size先表示的宽再表示的高trans_resize = transforms.Resize(min(w, h) // 2)    # 缩放为原来的1/2
  img_resize = trans_resize(image)  # 对PIL进行缩放
  writer.add_image('Resize', trans_totensor(img_resize))  # 因为在tensorboard中显示，所以需要转换为tensor或numpy类型trans_resize = transforms.Resize(min(w, h) // 4)    # 缩放为原来的1/4
  img_resize_tensor = trans_resize(img_tensor)
  writer.add_image('Resize', img_resize_tensor, 1)# 4.compose 组合这些操作
  trans_compose = transforms.Compose([transforms.Resize(min(w, h) // 2), transforms.ToTensor(), transforms.Normalize([0.5, 0.5, 0.5], [0.5, 0.5, 0.5])])
  img_campose = trans_compose(image)  # image是PIL.Image格式
  writer.add_image('Compose', img_campose)# 5.Randomcrop 随机裁剪
  trans_randomcrop = transforms.RandomCrop(min(w, h) // 4)    # 从原图中任意位置裁剪1/4
  # img_ranomcrop = trans_randomcrop(img_tensor)
  for i in range(10):img_ranomcrop = trans_randomcrop(img_tensor)writer.add_image('RandomCrop', img_ranomcrop, i)# close()一定要记得写啊！
  writer.close()