Tag Archives: Computer vision

[Solved] cv2.error: OpenCV(4.6.0) D:\a\opencv-python\opencv-python\opencv\modules\……

Project Scenarios

Run the opencv official website example code facedetect.py

#!/usr/bin/env python

face detection using haar cascades

    facedetect.py [--cascade <cascade_fn>] [--nested-cascade <cascade_fn>] [<video_source>]

# Python 2/3 compatibility
from __future__ import print_function

import numpy as np
import cv2 as cv

# local modules
from video import create_capture
from common import clock, draw_str

def detect(img, cascade):
    rects = cascade.detectMultiScale(img, scaleFactor=1.3, minNeighbors=4, minSize=(30, 30),
    if len(rects) == 0:
        return []
    rects[:,2:] += rects[:,:2]
    return rects

def draw_rects(img, rects, color):
    for x1, y1, x2, y2 in rects:
        cv.rectangle(img, (x1, y1), (x2, y2), color, 2)

def main():
    import sys, getopt

    args, video_src = getopt.getopt(sys.argv[1:], '', ['cascade=', 'nested-cascade='])
        video_src = video_src[0]
        video_src = 0
    args = dict(args)
    cascade_fn = args.get('--cascade', "data/haarcascades/haarcascade_frontalface_alt.xml")
    nested_fn = args.get('--nested-cascade', "data/haarcascades/haarcascade_eye.xml")

    cascade = cv.CascadeClassifier(cv.samples.findFile(cascade_fn))
    nested = cv.CascadeClassifier(cv.samples.findFile(nested_fn))
    cam = create_capture(video_src, fallback='synth:bg={}:noise=0.05'.format(cv.samples.findFile('data/lena.jpg')))#此处的data文件夹是从opencv示例simple包中复制到该项目中。

    while True:
        _ret, img = cam.read()
        gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
        gray = cv.equalizeHist(gray)

        t = clock()
        rects = detect(gray, cascade)
        vis = img.copy()
        draw_rects(vis, rects, (0, 255, 0))
        if not nested.empty():
            for x1, y1, x2, y2 in rects:
                roi = gray[y1:y2, x1:x2]
                vis_roi = vis[y1:y2, x1:x2]
                subrects = detect(roi.copy(), nested)
                draw_rects(vis_roi, subrects, (255, 0, 0))
        dt = clock() - t

        draw_str(vis, (20, 20), 'time: %.1f ms' % (dt*1000))
        cv.imshow('facedetect', vis)

        if cv.waitKey(5) == 27:


if __name__ == '__main__':

Problem description

Running the above code reports the following error:

[ WARN:[email protected]] global D:\a\opencv-python\opencv-python\opencv\modules\core\src\utils\samples.cpp (61) cv::samples::findFile cv::samples::findFile('data/haarcascades/haarcascade_frontalface_alt.xml') => ''
Traceback (most recent call last):
  File "E:\Pycharm\Pycharm7\facedetect.py", line 81, in <module>
  File "E:\Pycharm\Pycharm7\facedetect.py", line 48, in main
    cascade = cv.CascadeClassifier(cv.samples.findFile(cascade_fn))
cv2.error: OpenCV(4.6.0) D:\a\opencv-python\opencv-python\opencv\modules\core\src\utils\samples.cpp:64: error: (-2:Unspecified error) OpenCV samples: Can't find required data file: data/haarcascades/haarcascade_frontalface_alt.xml in function 'cv::samples::findFile'

Cause analysis:

According to the error location:

cascade = cv.CascadeClassifier(cv.samples.findFile(cascade_fn))

It can be found that the file paths of “haarcascade_frontalface_alt.xml” and “data/haarcascades/haarcascade_eye.xml” are not correct.


“haarcascade_frontalface_alt.xml” and “data/haarcascades/haarcascade_eye.xml” are under the cv2 package installed in python, just change the path in the code to a relative path.

The code is changed as follows:

cascade_fn = args.get('--cascade', "D:/Python/yingyong/Lib/site-packages/cv2/data/haarcascades/haarcascade_frontalface_alt.xml")
    nested_fn  = args.get('--nested-cascade', "D:/Python/yingyong/Lib/site-packages/cv2/data/haarcascades/haarcascade_eye.xml")

Run again to run normally.

[Solved] Mindspore 1.3.0 Compile Error: CMake Error at cmake/utils

[Function Module].
Compile mindspore 1.3.0 with error CMake Error at cmake/utils.cmake:301 (message): Failed patch:

[Steps & Problems]
1. The compilation process after executing bash build.sh -e ascend gives an error, as follows:

-- Build files have been written to: /root/mindspore-v1.3.0/build/mindspore/_deps/icu4c-subbuild
[100%] Built target icu4c-populate
icu4c_SOURCE_DIR : /root/mindspore-v1.3.0/build/mindspore/_deps/icu4c-src
patching /root/mindspore-v1.3.0/build/mindspore/_deps/icu4c-src -p1 < /root/mindspore-v1.3.0/build/mindspore/_ms_patch/icu4c.patch01
patching file icu4c/source/runConfigureICU
Reversed (or previously applied) patch detected!  Assume -R?[n]
Apply anyway?[n]
Skipping patch.
1 out of 1 hunk ignored -- saving rejects to file icu4c/source/runConfigureICU.rej
CMake Error at cmake/utils.cmake:301 (message):
  Failed patch:
Call Stack (most recent call first):
  cmake/external_libs/icu4c.cmake:36 (mindspore_add_pkg)
  cmake/mind_expression.cmake:85 (include)
  CMakeLists.txt:51 (include)

-- Configuring incomplete, errors occurred!
See also "/root/mindspore-v1.3.0/build/mindspore/CMakeFiles/CMakeOutput.log".
See also "/root/mindspore-v1.3.0/build/mindspore/CMakeFiles/CMakeError.log".

This situation is usually due to the failure of the last compilation on the way, try to compile again, please try to deal with the following.

rm -rf mindspore/build/mindspore/_deps/icu*

Then retry the compilation.

[Solved] GDAL+OPENCV often reports errors when processing remote sensing impacts

I found that every time I use the opencv package to process remote sensing images, it often reports an error, even though it has become uint format.
This time I found out that some of them only support three channels, my binary image is one channel, the error of storing the result is because I need to save the result of 1 channel, mine is three channels
so it is necessary to convert 1 channel to 3 channels back and forth ` img1 = np.array(b1)

# img2 = np.dtype(img1, np.uint8)
img = np.expand_dims(img1, axis=2)
img = np.concatenate((img, img, img), axis=-1)

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

ret, binary = cv2.threshold(gray, 127, 255, cv2.THRESH_BINARY)

contours, hierarchy = cv2.findContours(binary, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
# contours = cv2.findContours(img)
dilate = cv2.fillPoly(img, [contours[1]],(255,15,15))
cv2.imshow("filled binary", dilate)`


[Solved] error: (-215:Assertion failed) !_src.empty() in function ‘cv::cvtColor‘

Error Message:

error: (-215:Assertion failed) !_src.empty() in function ‘cv::cvtColor’

cv2.error: OpenCV(4.6.0) D:\a\opencv-python\opencv-python\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'


Path read error


Original code

videos_src_path = "D:\pythonProject\python3.9\dataset\image\baozi_image\3.png"
frame = cv2.imread(videos_src_path)

Press the following to modify the read path

videos_src_path = "D:/pythonProject/python3.9/dataset/image/baozi_image/3.png"
#or  videos_src_path = r" D:\pythonProject\python3.9\dataset\image\baozi_image\3.png"
frame = cv2.imread(videos_src_path)


How to Solve Ubuntu18 Compile Kalibr Error (Various Errors)

Opencv-3.4.13 is too new, and errors will be encountered during the compilation of kalibr. The summary is as follows:

Error 1: sudo pip install python-igraph –upgrade failed


sudo apt-get install python-igraph

Error 2:

Could not find a package configuration file provided by “code_utils” with
any of the following names:


  1. You need to put the following sentence in the sumpixel_test.cpp file
    #include “backward.hpp”
    to this line
    #include “code_utils/backward.hpp”
  2. Put code_utils into the workspace first, then catkin_ws once, then put imu_utils, then compile


Error 3: catkin build -DCMAKE_BUILD_TYPE=Release -j4 errors during compilation

3-1 error reporting:

 error: ‘CV_GRAY2RGB’ was not declared in this scope
     cv::cvtColor(imageCopy1, imageCopy1, CV_GRAY2RGB);
 error: ‘CV_TERMCRIT_ITER’ was not declared in this scope
         cv::TermCriteria(CV_TERMCRIT_EPS + CV_TERMCRIT_ITER, 30, 0.1));

error: ‘CV_TERMCRIT_EPS’ was not declared in this scope
         cv::TermCriteria(CV_TERMCRIT_EPS + CV_TERMCRIT_ITER, 30, 0.1));

3-1 solution: add a header file to the corresponding file:

#include <opencv2/imgproc/types_c.h>


3-2 cvstartwindowthread() error:

Change 3-2 to:



3-3 changed to



3-4 changed to


3-5 CV_ LOAD_ IMAGE_ Grayscale error:

Change 3-5 to



Change 3-6 to



3-7 changed to


3-8 CV_MINMAX error:

3-8 changed to



3-9 changed to



3-10 changed to


3-11 error: error: aggregate ‘std::ofstream out_t’ has incomplete type and cannot be defined std::ofstream out_t;
3-11 Solution: add the header file as below:

#include <fstream>

[Solved] pytorch loss.backward() Error: RuntimeError: Function AddBackward0 returned an invalid gradient at index 1…

How to Solve pytorch loss.backward() Error

The specific errors are as follows:

In fact, the error message makes it clear that the error is caused by device inconsistency in the backpropagation process.
In the code, we first load all input, target, model, and loss to the GPU via .to(device). But when calculating the loss, we initialize a loss ourselves
loss_1 = torch.tensor(0.0)
This way by default loss_1 is loaded on the CPU.
The final execution loss_seg = loss + loss_1
results in the above error for loss_seg.backward().

Modification method:
loss_1 = torch.tensor(0.0)
loss_1 = torch.tensor(0.0).to(device)
loss_1 = torch.tensor(0.0).cuda()

[Solved] ValueError: Error when checking input: expected conv2d_input to have 4 dimensions

Error Messages:

ValueError: Error when checking input: expected conv2d_input to have 4 dimensions, but got array with shape (150, 150, 3)

image = mpimg.imread("./ima/b.jpg")
image = image/255
classe = model.predict(image, batch_size=1)

the input format is incorrect
standardize the dataset

Specific solutions:

image = mpimg.imread("./ima/b.jpg")
image = image.reshape(image.shape(1,150,150,3)/255
classe = model.predict(image, batch_size=1)

[Solved] error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows

Error: error: (-2:Unspecified error) The function is not implemented. Rebuild the library with Windows

I’m on windows, and when running an image motion blur algorithm from the cv-python library, this error is suddenly reported.
Searching for similar problems has said that the path to read the image is wrong, and reinstalling a higher version of the cv library, but not all of them are useless.
All the functions under the cv2 class are not working.


pip uninstall opencv-python 


pip install opencv-python

Just reinstall this package. I don’t know the cause. The problem occurred after I installed the evaluations package. It should be caused by the conflict between versions
stackoverflow: https://stackoverflow.com/questions/67120450/error-2unspecified-error-the-function-is-not-implemented-rebuild-the-libra

[Solved] Opencv Call yolov3 Error: IndexError: invalid index to scalar variable

Call the weight file of yolov3 with OpenCV to obtain the names of the three scale output layers and report an error

ln = [ln[i[0] - 1] for i in net.getUnconnectedOutLayers()]

Error reporting
indexerror: invalid index to scalar variable

This code was a few years ago. It may be a problem with the version. Now it will report an error

Remove [0] and modify as below:

ln = [ln[i - 1] for i in net.getUnconnectedOutLayers()]

[Solved] headless pyrender offscreen render Error: OpenGL.error.GLError: GLError(err = 12296,

Error description

When running vibe, the CentOS server without display is used. When using pyrender for off screen rendering, errors are reported OpenGL.error.GLError: GLError(err = 12296), as follows:

Traceback (most recent call last):
  File "demo.py", line 416, in <module>
  File "demo.py", line 278, in main
    renderer = Renderer(resolution=(orig_width, orig_height), orig_img=True, wireframe=args.wireframe)
  File "***/VIBE/lib/utils/renderer.py", line 60, in __init__
  File "***/anaconda3/envs/vibe-env/lib/python3.7/site-packages/pyrender/offscreen.py", line 31, in __init__
  File "***/anaconda3/envs/vibe-env/lib/python3.7/site-packages/pyrender/offscreen.py", line 134, in _create
  File "***/anaconda3/envs/vibe-env/lib/python3.7/site-packages/pyrender/platforms/egl.py", line 177, in init_context
    assert eglInitialize(self._egl_display, major, minor)
  File "***/anaconda3/envs/vibe-env/lib/python3.7/site-packages/OpenGL/platform/baseplatform.py", line 409, in __call__
    return self( *args, **named )
  File "***/anaconda3/envs/vibe-env/lib/python3.7/site-packages/OpenGL/error.py", line 232, in glCheckError
    baseOperation = baseOperation,
OpenGL.error.GLError: GLError(
        err = 12296,
        baseOperation = eglInitialize,
        cArguments = (
                <OpenGL._opaque.EGLDisplay_pointer object at 0x7f883a03a170>,
        result = 0


Ubuntu: https://pyrender.readthedocs.io/en/latest/install/index.html#installmesa Use OSMesa to offscreen render.

It is more convenient to use · CONDA · to install osmesa as follows:

conda install osmesa

Note: after installing osmesa, reinstall pyopengl, otherwise an error will still be reported, as follows:

pip uninstall pyopengl
git clone https://github.com/mmatl/pyopengl.git
pip install ./pyopengl

Specify PYOPENGL_PLATFORM before running the scriptis osmesa , as follows:

# demp.py
import os
# os.environ['PYOPENGL_PLATFORM'] = 'egl'
os.environ['PYOPENGL_PLATFORM'] = 'osmesa'

Note: os.environ[‘PYOPENGL_PLATFORM’] = ‘osmesa’ should ideally follow import os to ensure that PYOPENGL_PLATFORM is changed to osmesa before using render, or you can explicitly specify os.environ before using render specifically [‘PYOPENGL_PLATFORM’] = ‘osmesa’.

[Solved] mmdetection Error: ImportError: /home/user/repos/mmdetection/mmdet/ops/dcn/deform_conv_cuda.cpython-37m-x

Environment configuration: torch 1.11.0 + CUDA 11.3 (latest)

Use mmdetection to infer:

from mmdet.apis import init_detector, inference_detector

Errors are reported as follows:

ImportError: /home/user/repos/mmdetection/mmdet/ops/dcn/deform_conv_cuda.cpython-37m-x86_64-linux-gnu.so: undefined symbol: _ZN6caffe26detail37_typeMetaDataInstance_preallocated_32E


The problem has been solved. The reason for the error is that the pytorch version is too new. Although openmmlab supports the latest version, it will still cause the error.


Degrade the pytorch version to torch 1.6.0 + cu102, query the official GitHub of openmmlab, uninstall and reinstall mmcv 1.3.9, and re run the mmdetection code to solve the error.

[Solved] size_from_dim: Assertion `dim >= 0 && (size_t)dim < sizes_.size()` failed.

Problems encountered

/home/optimizer-master/third_party/onnx_common/tensor.h:117: size_from_dim: Assertion dim >= 0 && (size_t)dim < sizes_.size() failed.


Problem description

When import onnx, I encountered the above problems



If there is an op operation that cannot be exported during onnx export, this error will be reported
How to Solve:
find the operation that cannot be exported and add a judgment. If you export onnx, the op will not be used. An example is as follows

def forward(self, x):
    if torch.onnx.is_in_onnx_export():# if onnx
        return x * self.act(x)/6
    else: # normally
        return x * self.act(x + 3)/6