why is my cv2.imread() call returning None?答案

【问题标题】：why is my cv2.imread() call returning None?why is my cv2.imread() call returning None?
【发布时间】：2022-12-26 21:31:41
【问题描述】：

I just want to cut the img to samll piece and save it , but somehow cannot save

import os
import cv2
import numpy as np
from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
import pytesseract


sorted_predict_xy_list = [ [71,180], [221,180], [371,180], [521,180], [671,180], [821,180],
[71,291], [221,291], [371,291], [521,291], [671,291], [821,291],
[71,402], [221,402], [371,402], [521,402], [671,402], [821,402],
[71,513], [221,513], [371,513], [521,513], [671,513], [821,513],
[71,624], [221,624], [371,624], [521,624], [671,624], [821,624] ]

image = cv2.imread("/home/student_DC/desktop/optimization_11_10/original_duplicate.png")
j = 0
while j < len(sorted_predict_xy_list) :
    temp_xy = sorted_predict_xy_list[j]
    x = temp_xy[0]
    y = temp_xy[1]
    small_txt_size_w = 65
    small_txt_size_h = 16
    new_crop = image[y:y+small_txt_size_h, x:x+small_txt_size_w]
    cv2.imwrite("/home/student_DC/desktop/optimization_11_10/output_11_10__001/x_{x}_y_{y}.png", new_crop)
    j+=1

output:

Traceback (most recent call last):
  File "/home/student_DC/desktop/optimization_11_10/draw_squar_on_duplicate_01N.py", line 26, in <module>
    cv2.imwrite("/home/student_DC/desktop/optimization_11_10/output_11_10__001/x_{x}_y_{y}.png", new_crop)
cv2.error: OpenCV(3.4.15) /tmp/pip-req-build-9opz8s5q/opencv/modules/imgcodecs/src/loadsave.cpp:741: error: (-215:Assertion failed) !_img.empty() in function 'imwrite'

by read through discussion Cv2.error : (-215:Assertion failed) !_img.empty() in function 'imwrite'
I'm checking my x, y is not empty

import os
import cv2
import numpy as np
from PIL import Image
from PIL import ImageDraw
from PIL import ImageFont
import pytesseract


sorted_predict_xy_list = [ [71,180], [221,180], [371,180], [521,180], [671,180], [821,180],
[71,291], [221,291], [371,291], [521,291], [671,291], [821,291],
[71,402], [221,402], [371,402], [521,402], [671,402], [821,402],
[71,513], [221,513], [371,513], [521,513], [671,513], [821,513],
[71,624], [221,624], [371,624], [521,624], [671,624], [821,624] ]

image = cv2.imread("/home/student_DC/desktop/optimization_11_10/original_duplicate.png")
j = 0
while j < len(sorted_predict_xy_list) :
    temp_xy = sorted_predict_xy_list[j]
    x = temp_xy[0]
    y = temp_xy[1]
    small_txt_size_w = 65
    small_txt_size_h = 16
    new_crop = image[y:y+small_txt_size_h, x:x+small_txt_size_w]
    print("x :" , x  , ",y :",y , ", x+small_txt_size_w", x+small_txt_size_w , ", y+small_txt_size_h :" , y+small_txt_size_h)
    j+=1

output:

Traceback (most recent call last):
  File "/home/student_DC/desktop/optimization_11_10/draw_squar_on_duplicate_01N.py", line 25, in <module>
    new_crop = image[y:y+small_txt_size_h, x:x+small_txt_size_w]
TypeError: 'NoneType' object is not subscriptable

so far I get here , but don't know how to slove my issue

【问题讨论】：

file does not exist or isn't where you thought it was, or it's corrupted. it is that simple. -- that other question you found doesn't deal with your error at all. it deals with an entirely different error. they just have the same consequence.
Both errors tell you the same thing: your 'image' variable does not exist or is emtpy. Two tips: (a) rename it, there's a decent chance that identifier is already taken by one of the libraries. (b) check that it exists by yourself first with mat.size() and mat.type()
@nick (1) none of the imports can possibly assign anything to the global image variable. renaming is pointless. if that's the entire code, I don't even see room for typos. in python, anundefinedvariable doesn't have a value. using it raises a NameError, but that didn't happen here. (2) .size() and .type() don't exist in python. it's all numpy arrays. -- clearly imread returned None. that's all there is to it.

标签： python opencv path

【解决方案1】：

I did not test.

To solve this error, we must remove the declaration of the new_crop variable and add image.append() on its own line.

image.append(y:y+small_txt_size_h, x:x+small_txt_size_w)
print("x :" , x  , ",y :",y , ", x+small_txt_size_w", x+small_txt_size_w , ", y+small_txt_size_h :" , y+small_txt_size_h)
j+=1

【讨论】：