Ipython cv2.imwrite() 不保存图像

Ipython cv2.imwrite() not saving image

提问by Niladri Chakraborty

I have written a code in python opencv. I am trying to write the processed image back to disk but the image is not getting saved and it is not showing any error(runtime and compilation) The code is

我在 python opencv 中写了一段代码。我正在尝试将处理后的图像写回磁盘，但图像没有被保存，也没有显示任何错误（运行时和编译）代码是

"""
Created on Wed Oct 19 18:07:34 2016

@author: Niladri
"""

import numpy as np  
import cv2  

if __name__ == '__main__':  
import sys  

img = cv2.imread('C:\Users\Niladri\Desktop\TexturesCom_LandscapeTropical0080_2_S.jpg')
if img is None:  
    print 'Failed to load image file:'
    sys.exit(1)  

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)  
h, w = img.shape[:2]  

eigen = cv2.cornerEigenValsAndVecs(gray, 15, 3)  
eigen = eigen.reshape(h, w, 3, 2)  # [[e1, e2], v1, v2]  
#flow = eigen[:,:,2] 
iter_n = 10
sigma = 5
str_sigma = 3*sigma
blend = 0.5
img2 = img
for i in xrange(iter_n):  
    print i,  

    gray = cv2.cvtColor(img2, cv2.COLOR_BGR2GRAY)  
    eigen = cv2.cornerEigenValsAndVecs(gray, str_sigma, 3)  
    eigen = eigen.reshape(h, w, 3, 2)  # [[e1, e2], v1, v2]  
    x, y = eigen[:,:,1,0], eigen[:,:,1,1] 
    print eigen

    gxx = cv2.Sobel(gray, cv2.CV_32F, 2, 0, ksize=sigma)  
    gxy = cv2.Sobel(gray, cv2.CV_32F, 1, 1, ksize=sigma)  
    gyy = cv2.Sobel(gray, cv2.CV_32F, 0, 2, ksize=sigma)  
    gvv = x*x*gxx + 2*x*y*gxy + y*y*gyy  
    m = gvv < 0  

    ero = cv2.erode(img, None)  
    dil = cv2.dilate(img, None)  
    img1 = ero  
    img1[m] = dil[m]  
    img2 = np.uint8(img2*(1.0 - blend) + img1*blend)  
#print 'done'
cv2.imshow('dst_rt', img2)
cv2.waitKey(0)
cv2.destroyAllWindows()

#cv2.imwrite('C:\Users\Niladri\Desktop\leaf_image_shock_filtered.jpg', img2)    



for i in xrange(iter_n):  
    print i,  

    gray = cv2.cvtColor(img2, cv2.COLOR_BGR2GRAY)  
    eigen = cv2.cornerEigenValsAndVecs(gray, str_sigma, 3)  
    eigen = eigen.reshape(h, w, 3, 2)  # [[e1, e2], v1, v2]  
    x, y = eigen[:,:,1,0], eigen[:,:,1,1] 
    print eigen

    gxx = cv2.Sobel(gray, cv2.CV_32F, 2, 0, ksize=sigma)  
    gxy = cv2.Sobel(gray, cv2.CV_32F, 1, 1, ksize=sigma)  
    gyy = cv2.Sobel(gray, cv2.CV_32F, 0, 2, ksize=sigma)  
    gvv = x*x*gxx + 2*x*y*gxy + y*y*gyy  
    m = gvv < 0  

    ero = cv2.erode(img, None)  
    dil = cv2.dilate(img, None)  
    img1 = dil  
    img1[m] = ero[m]  
    img2 = np.uint8(img2*(1.0 - blend) + img1*blend)  
print 'done'

#cv2.imwrite('D:\IP\tropical_image_sig5.bmp', img2)    


cv2.imshow('dst_rt', img2)
cv2.waitKey(0)
cv2.destroyAllWindows()

#cv2.imshow('dst_rt', img2)    

cv2.imwrite('C:\Users\Niladri\Desktop\tropical_image_sig5.bmp', img2)

Can anyone please tell me why it is not working. cv2.imshow is working properly(as it is showing the correct image). Thanks and Regards Niladri

谁能告诉我为什么它不起作用。cv2.imshow 工作正常（因为它显示了正确的图像）。感谢和问候 Niladri

回答by Jean-Fran?ois Fabre

As a general and absolute rule, you haveto protect your windows path strings (containing backslashes) with rprefix or some characters are interpreted (ex: \n,\b,\v,\xaaaaand \t, full list here):

作为一般和绝对规则，您必须使用r前缀或解释某些字符来保护您的 Windows 路径字符串（包含反斜杠）（例如：\n,\b,\v,\xaaaaand \t，完整列表在这里）：

so when doing this:

所以当这样做时：

cv2.imwrite('C:\Users\Niladri\Desktop\tropical_image_sig5.bmp', img2)

you're trying to save to C:\Users\Niladri\Desktop<TAB>ropical_image_sig5.bmp

你试图保存到 C:\Users\Niladri\Desktop<TAB>ropical_image_sig5.bmp

And the annoying thing with imreadand imwriteis that those functions don't throw exceptions on errors, but fail silently. imwritereturns False

而伴随着恼人的事情imread，并imwrite为那些功能不扔在错误的异常，只是默默地失败。imwrite返回False

>>> cv2.imread("D:/nonexisting.jpg")  # this returns None, no error
>>> s = cv2.imread("D:/sloth_book.jpg")  # this works
>>> s
array([[[250, 250, 250],
        [246, 246, 246],
        [255, 255, 255],
        ...,
>>> cv2.imwrite("inexistent_dir/file.jpg",s)  # dir doesn't exist, write fails
False

So you have to check return value of those functions.

所以你必须检查这些函数的返回值。

Do this:

做这个：

if not cv2.imwrite(r'C:\Users\Niladri\Desktop\tropical_image_sig5.bmp', img2):
     raise Exception("Could not write image")

Note: the read works fine because "escaped" uppercase letters have no particular meaning in python 2 (\Uand \Nhave a meaning in python 3 so it wouldn't have worked)

注意：读取工作正常，因为“转义”大写字母在 python 2 中没有特殊含义（\U并且\N在 python 3 中具有含义，因此它不会起作用）

And if there's an error, the program now complains loudly.

如果出现错误，程序现在会大声抱怨。

回答by R. S. Nikhil Krishna

As Jean suggested, the error is due to the \ being interpretted as an escape sequence. It is hence always safer to use os.path.join()as it is more cross platform and you need not worry about the escape sequence problem. For instance, in your case, you further need not worry about the first few arguments, as that is your home directory

正如 Jean 所建议的，错误是由于 \ 被解释为转义序列。因此使用os.path.join()它总是更安全，因为它更跨平台，您不必担心转义序列问题。例如，在您的情况下，您无需担心前几个参数，因为那是您的主目录

import os
cv2.imwrite(os.path.join(os.path.expanduser('~'),'Desktop','tropical_image_sig5.bmp'), img2)

os.path.expanduser('~')will directly return your home directory.

os.path.expanduser('~')将直接返回您的主目录。

回答by Jeff Blumenthal

If you want to have the paths in your code portable, look into pathlib.

如果您希望代码中的路径可移植，请查看 pathlib。

https://docs.python.org/3/library/pathlib.html

https://docs.python.org/3/library/pathlib.html