深度学习代码片段合集

计算数据集的mean和std

"""
in this script, we calculate the image per channel mean and standard
deviation in the training set, do not calculate the statistics on the
whole dataset, as per here http://cs231n.github.io/neural-networks-2/#datapre
"""

import numpy as np
from os import listdir
from os.path import join, isdir
from glob import glob
import cv2
import timeit

# number of channels of the dataset image, 3 for color jpg, 1 for grayscale img
# you need to change it to reflect your dataset
CHANNEL_NUM = 3


def cal_dir_stat(root):
    cls_dirs = [d for d in listdir(root) if isdir(join(root, d))]
    pixel_num = 0 # store all pixel number in the dataset
    channel_sum = np.zeros(CHANNEL_NUM)
    channel_sum_squared = np.zeros(CHANNEL_NUM)

    for idx, d in enumerate(cls_dirs):
        print("#{} class".format(idx))
        im_pths = glob(join(root, d, "*.jpg"))

        for path in im_pths:
            im = cv2.imread(path) # image in M*N*CHANNEL_NUM shape, channel in BGR order
            im = im/255.0
            pixel_num += (im.size/CHANNEL_NUM)
            channel_sum += np.sum(im, axis=(0, 1))
            channel_sum_squared += np.sum(np.square(im), axis=(0, 1))

    bgr_mean = channel_sum / pixel_num
    bgr_std = np.sqrt(channel_sum_squared / pixel_num - np.square(bgr_mean))
    
    # change the format from bgr to rgb
    rgb_mean = list(bgr_mean)[::-1]
    rgb_std = list(bgr_std)[::-1]
    
    return rgb_mean, rgb_std

# The script assumes that under train_root, there are separate directories for each class
# of training images.
train_root = "/hd1/jdhao/firearm-dataset/train/"
start = timeit.default_timer()
mean, std = cal_dir_stat(train_root)
end = timeit.default_timer()
print("elapsed time: {}".format(end-start))
print("mean:{}
std:{}".format(mean, std))