pytorch做標準化利用transforms.Normalize(mean_vals, std_vals),其中常用數據集的均值方差有:
if 'coco' in args.dataset:
mean_vals = [0.471, 0.448, 0.408]
std_vals = [0.234, 0.239, 0.242]
elif 'imagenet' in args.dataset:
mean_vals = [0.485, 0.456, 0.406]
std_vals = [0.229, 0.224, 0.225]
計算自己數據集圖像像素的均值方差:
import numpy as np
import cv2
import random
# calculate means and std
train_txt_path = './train_val_list.txt'
CNum = 10000 # 挑選多少圖片進行計算
img_h, img_w = 32, 32
imgs = np.zeros([img_w, img_h, 3, 1])
means, stdevs = [], []
with open(train_txt_path, 'r') as f:
lines = f.readlines()
random.shuffle(lines) # shuffle , 隨機挑選圖片
for i in tqdm_notebook(range(CNum)):
img_path = os.path.join('./train', lines[i].rstrip().split()[0])
img = cv2.imread(img_path)
img = cv2.resize(img, (img_h, img_w))
img = img[:, :, :, np.newaxis]
imgs = np.concatenate((imgs, img), axis=3)
# print(i)
imgs = imgs.astype(np.float32)/255.
for i in tqdm_notebook(range(3)):
pixels = imgs[:,:,i,:].ravel() # 拉成一行
means.append(np.mean(pixels))
stdevs.append(np.std(pixels))
# cv2 讀取的圖像格式爲BGR,PIL/Skimage讀取到的都是RGB不用轉
means.reverse() # BGR --> RGB
stdevs.reverse()
print("normMean = {}".format(means))
print("normStd = {}".format(stdevs))
print('transforms.Normalize(normMean = {}, normStd = {})'.format(means, stdevs))