torch 中各種圖像格式轉換

• PIL：使用python自帶圖像處理庫讀取出來的圖片格式
• numpy：使用python-opencv庫讀取出來的圖片格式
• tensor：pytorch中訓練時所采取的向量格式（當然也可以說圖片）

PIL與Tensor相互轉換

import torch
from PIL import Image
import matplotlib.pyplot as plt

# loader使用torchvision中自帶的transforms函數
loader = transforms.Compose([
    transforms.ToTensor()])  

unloader = transforms.ToPILImage()

# 輸入圖片地址
# 返回tensor變量
def image_loader(image_name):
    image = Image.open(image_name).convert('RGB')
    image = loader(image).unsqueeze(0)
    return image.to(device, torch.float)

# 輸入PIL格式圖片
# 返回tensor變量
def PIL_to_tensor(image):
    image = loader(image).unsqueeze(0)
    return image.to(device, torch.float)

# 輸入tensor變量
# 輸出PIL格式圖片
def tensor_to_PIL(tensor):
    image = tensor.cpu().clone()
    image = image.squeeze(0)
    image = unloader(image)
    return image

#直接展示tensor格式圖片
def imshow(tensor, title=None):
    image = tensor.cpu().clone()  # we clone the tensor to not do changes on it
    image = image.squeeze(0)  # remove the fake batch dimension
    image = unloader(image)
    plt.imshow(image)
    if title is not None:
        plt.title(title)
    plt.pause(0.001)  # pause a bit so that plots are updated

#直接保存tensor格式圖片
def save_image(tensor, **para):
    dir = 'results'
    image = tensor.cpu().clone()  # we clone the tensor to not do changes on it
    image = image.squeeze(0)  # remove the fake batch dimension
    image = unloader(image)
    if not osp.exists(dir):
        os.makedirs(dir)
    image.save('results_{}/s{}-c{}-l{}-e{}-sl{:4f}-cl{:4f}.jpg'
               .format(num, para['style_weight'], para['content_weight'], para['lr'], para['epoch'],
                       para['style_loss'], para['content_loss']))

numpy 與 tensor相互轉換

import cv2
import torch
import matplotlib.pyplot as plt

def toTensor(img):
    assert type(img) == np.ndarray,'the img type is {}, but ndarry expected'.format(type(img))
    img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
    img = torch.from_numpy(img.transpose((2, 0, 1)))
    return img.float().div(255).unsqueeze(0)  # 255也可以改為256

def tensor_to_np(tensor):
    img = tensor.mul(255).byte()
    img = img.cpu().numpy().squeeze(0).transpose((1, 2, 0))
    return img

def show_from_cv(img, title=None):
    img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
    plt.figure()
    plt.imshow(img)
    if title is not None:
        plt.title(title)
    plt.pause(0.001)


def show_from_tensor(tensor, title=None):
    img = tensor.clone()
    img = tensor_to_np(img)
    plt.figure()
    plt.imshow(img)
    if title is not None:
        plt.title(title)
    plt.pause(0.001)

N張圖片一起轉換.

# 將 N x H x W X C 的numpy格式圖片轉化為相應的tensor格式
def toTensor(img):
    img = torch.from_numpy(img.transpose((0, 3, 1, 2)))
    return img.float().div(255).unsqueeze(0)

參考:https://oldpan.me/archives/pytorch-tensor-image-transform