abidrahmank / opencv2-python-tutorials

This repo contains tutorials on OpenCV-Python library using new cv2 interface

OpenCV2-Python-Guide

This repo contains tutorials on OpenCV-Python library using new cv2 interface

IMP - This tutorial is meant for OpenCV 3x version. Not OpenCV 2x

IMP - This tutorial is meant for OpenCV 3x version. Not OpenCV 2x

IMP - This tutorial is meant for OpenCV 3x version. Not OpenCV 2x

Please try the examples with OpenCV 3x before sending any bug reports

Data files

The input data used in these tutorials are given in Data folder

Online

• For official tutorials, please visit : http://docs.opencv.org/trunk/doc/py_tutorials/py_tutorials.html
• https://opencv-python-tutroals.readthedocs.org/en/latest/index.html - This is only for checking. May contain lots of errors, please stick to the official tutorials.

Offline

To build docs from source,

• Install sphinx
• Download/Clone this repo and navigate to the base folder
• run command : make html , html docs will be available in build/html/ folder

opencv2-python-tutorials's Issues

error while reading a video

error: OpenCV(4.0.0) C:\projects\opencv-python\opencv\modules\imgproc\src\color.cpp:181: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor @abidrahmank

Cannot detect the circle

I tried using the function cv2.HoughCircles but it doesnt detect the hand drawn circle on the paper. Can anybody help me with this?

`
import numpy as np
import imutils
import cv2

image = cv2.imread("images/136_5cm.png")
output = image.copy()
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
#gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
#gray = cv2.GaussianBlur(gray, (5, 5), 0)

detect circles in the image

print('hello')
circles = cv2.HoughCircles(gray, cv2.HOUGH_GRADIENT, 1.4 ,100,)

ensure at least some circles were found

if circles is not None:
# convert the (x, y) coordinates and radius of the circles to integers
circles = np.round(circles[0, :]).astype("int")
print(circles)

# loop over the (x, y) coordinates and radius of the circles
for (x, y, r) in circles:
	# draw the circle in the output image, then draw a rectangle
	# corresponding to the center of the circle
	cv2.circle(output, (x, y), r, (0, 255, 0), thickness=4, lineType=8, shift=0)
	cv2.rectangle(output, (x - 5, y - 5), (x + 5, y + 5), (0, 128, 255), -1)

# show the output image
cv2.imshow("output", np.hstack([image, output]))
cv2.waitKey(0)`

Re-projection error example code is not correct

http://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_calib3d/py_calibration/py_calibration.html?highlight=findcirclesgrid

Here is the code shown in the link provided.

mean_error = 0
for i in xrange(len(objpoints)):
    imgpoints2, _ = cv2.projectPoints(objpoints[i], rvecs[i], tvecs[i], mtx, dist)
    error = cv2.norm(imgpoints[i],imgpoints2, cv2.NORM_L2)/len(imgpoints2)
    tot_error += error

print "total error: ", mean_error/len(objpoints)

The mean_error and tot_error are messed up

Small wording mistake

I was reading the docs and got tripped up by this sentence.

"It is more better and faster way to draw a group of lines than calling cv2.line() for each line."

I think the sentence could be improved by removing 'more better'. Here is my suggested improvement.

"To draw groups of lines, calling cv2.polylines() is better and faster than it is to call cv2.line() for each line.

Link to the location in docs

link

Thanks for writing the docs, I have found them useful.
best,

• wisemonkey

cv2.SIFT() doesn't work in Opencv2.4.9

Hi I tried your code. it gives an error regarding no module SIFT for cv2 is available while cv2.FeautureDetector_create("SIFT") work. could you let me know why?

Code Mistake on Calibration Tutorials

Hello,
I made the camera calibration lesson last night quite useful. Thanks for this.
However, I think there is a mistake in the subtopic about "Re projection error". In the code, mean_error is defined by the initial condition 0. Also, the end of the block of code is printed with a len(objpoints). But that code always "print 0". If It is possible, could you correct it?

https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_calib3d/py_calibration/py_calibration.html

distance metric used in knn

I want to know distance metric used in knn , and how to normalize distance in n dimension .do i decide the threshold over the distance

Link error

Hello guys,
nice work at the manuals and tutorials.
About the link to ipython profile there is a error:
Instead
http://pynash.org/2013/03/06/timing-and-profiling.html
the correct link is:
http://pynash.org/2013/03/06/timing-and-profiling/

Hope it will be helpfull

a few errors in feature matching articles

Hello, just tried your tutorial on python openCV (doing stuff on pattern matching, and your articles are great!), yet met a few errors:

a call to cv2.LINE_AA causes an error - no-module-blah-blah… after digging a little around cv2, found that it should be cv2.CV_AA.

Next culprit is img3 = cv2.drawMatches(img1,kp1,img2,kp2,good,None,**draw_params) which returns module object has no attribute 'drawMatches' and theres no drawMatches method in dir(cv2)... couldnot resolve this one and google is of little help here.

using cv2 version 2.4.7
installed via macports and pip
osx

cv2.findContours() gives error

I am using this function but it shows the following error:

contours, hierarchy = cv2.findContours(canny.copy(),cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE) :

error: ......\opencv-2.4.12\modules\core\src\matrix.cpp:236: error: (-215) step[dims-1] == (size_t)CV_ELEM_SIZE(flags) in function cv::Mat::create

Has it happened to anyone?

Itseez sample pictures are now located in a different location.

New location (for box.jpg and box_in_scene.jpg):

https://github.com/opencv/opencv/tree/master/samples/data

license

What license is this released under? May I suggest you use this and add appropriate info to the repo

should check end of the video when play it

add the following code
if ret == False: # check end of the video by checking this return value.
break
after
ret, frame = cap.read()

if not doing this, there will be a fatal error when play a video

Broken Link to StackOverflow

The current link to stack overflow is listed as a relative path, instead of an absolute path. This issue is addressed in pull request #93 linked below.

If you find this issue to be legitimate, and my pull request (as linked) to be in the best interest of the project, please add a +1 reaction so this issue may be quickly resolved.

Improper Link

Documentation Page

My Fix

Provide pip method for installing numpy and matplotlib

After installing python, numpy & matplotlib from given links and copying cv2.pyd, I get error:
opencv ImportError: numpy.core.multiarray failed to import

...while running the following code:

>>> import cv2
>>> print cv2.__version__

But, installing through pip, everything works fine.

About py_maths_tools

The py_maths_tools is blank, but the SVD and PCA are really useful, may I see them anywhere else?

README error

The link in README.md failed.

For official tutorials, please visit : http://docs.opencv.org/trunk/doc/py_tutorials/py_tutorials.html

It return 404 Not Found.

Error in importing pngmath for sphinx v2.0.1

When I want to "make html" for sphinx v2.0.1 in windows, I found an error in the making which said could not find pngmath module for Sphinx.
I searched and find that I must change 'pngmath' to 'imgmath' in ./source/conf.py
It was solved. I just share my experience
Sincerely

Link to slow.flv

Hi,
Please share the direct link to slow.flv used in Lukas-Kanade dense optical flow.
Thanks!

Youtube video link is broken

on this page, at the bottom is a video link:

https://github.com/abidrahmank/OpenCV2-Python-Tutorials/blob/master/source/py_tutorials/py_ml/py_svm/py_svm_opencv/py_svm_opencv.rst

It also happens on the readthedocs version, basically what it's doing is adding github.com.... in front of the link, so that clicking it won't get you to youtube.

Bug in camera tutorial

Hi,

While walking through the tutorial of the camera calibration I found two bugs (under "setup"):

The code lines:
corners2 = cv2.cornerSubPix(gray,corners,(11,11),(-1,-1),criteria)

and:
img = cv2.drawChessboardCorners(img, (7,6), corners2,ret)

always output none, instead I thing they should be just:
cv2.cornerSubPix(gray,corners,(11,11),(-1,-1),criteria)

cv2.drawChessboardCorners(img, (7,6), corners2,ret)

The functions modify the given img directly

Cheers,

Martijn

surf = cv2.SURF(400) AttributeError: 'module' object has no attribute 'SURF'

I have been following official documentation and while implementing surf I get this error
surf = cv2.SURF(400)
AttributeError: 'module' object has no attribute 'SURF'

Issue while face recognition

My code is this :

import cv2

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv2.CascadeClassifier('haarcascade_eye.xml')


def detect(gray, frame):
    faces = face_cascade.detectMultiScale(gray, 1.3, 5)
    for (x, y, w, h) in faces:
        cv2.rectangle(frame, (x, y), (x+w, y+h), (255, 0, 0), 2)
        roi_gray = gray[y:y+h, x:x+w]
        roi_color = frame[y:y+h, x:x+w]
        eyes = eye_cascade.detectMultiScale(roi_gray, 1.1, 3)
        for (ex, ey, ew, eh) in eyes:
            cv2.rectangle(roi_color, (ex, ey), (ex+ew, ey+eh), (0, 255, 0), 2)
    return frame
video_capture = cv2.VideoCapture(1)
while True:
    _, frame = video_capture.read()
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    canvas = detect(gray, frame)
    cv2.imshow('Video', canvas)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
video_capture.release()
cv2.destroyAllWindows()

ERROR:

runfile('C:/Users/Akhil/Desktop/OpenCV/Computer Vision A-Z/Module 1 - Face Recognition/face_recognition_nocomment.py', wdir='C:/Users/Akhil/Desktop/OpenCV/Computer Vision A-Z/Module 1 - Face Recognition')
Traceback (most recent call last):

  File "<ipython-input-15-99eb78ea8252>", line 1, in <module>
    runfile('C:/Users/Akhil/Desktop/OpenCV/Computer Vision A-Z/Module 1 - Face Recognition/face_recognition_nocomment.py', wdir='C:/Users/Akhil/Desktop/OpenCV/Computer Vision A-Z/Module 1 - Face Recognition')

  File "C:\Users\Akhil\Anaconda3\envs\virtual_platform\lib\site-packages\spyder\utils\site\sitecustomize.py", line 710, in runfile
    execfile(filename, namespace)

  File "C:\Users\Akhil\Anaconda3\envs\virtual_platform\lib\site-packages\spyder\utils\site\sitecustomize.py", line 101, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

  File "C:/Users/Akhil/Desktop/OpenCV/Computer Vision A-Z/Module 1 - Face Recognition/face_recognition_nocomment.py", line 21, in <module>
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

error: ..\..\..\modules\imgproc\src\color.cpp:7456: error: (-215) scn == 3 || scn == 4 in function cv::ipp_cvtColor

What to do now :(

links broken

In README

http://docs.opencv.org/trunk/doc/py_tutorials/py_tutorials.html

doesn't work.

https://opencv-python-tutroals.readthedocs.org/en/latest/index.html

you spelled 'tutorials' wrong.

Readthedocs url says "tutroals"

Typo.

Installation instructions for 3.x version

I followed the instruction for installing opencv from the tutorials and ended up with 2.4.x version and later encountered problem while going through the instructions.
There is no instruction for installing the 3.x version.
Sourceforge has only 2.4.x branches and Github repo also has only 2.4 branches on master.
It would be nice to have detailed instructions for installing 3.x version.

Segmentation Fault in Trackbar Tutorial

For some odd reason, OpenCV throws a segmentation fault in the trackbar tutorial.
It still reports a segmentation fault when using gdb, but it somehow doesn't when using VSCode's Debugger.
Going through by myself, the script only crashes python when using four or more Trackbars. Commenting out everything related to the switch trackbar eliminated the issue, but when I attempted to add another trackbar, it crashed again.

Any insight into what may be causing this issue?

Jupyter Notebook support

https://github.com/abidrahmank/OpenCV2-Python-Tutorials/blob/master/source/py_tutorials/py_gui/py_drawing_functions/py_drawing_functions.rst

The color display differently using JupyterNoteBook using

plt.imshow(img)
plt.xticks([]), plt.yticks([]) # to hide tick values on X and Y axis
plt.show()

since

(255,0,0) is color red
(0,0,255) is color blue

Thus, should be noted?

Can not make the tutorials into html

I download the project and make html according to the readme. But there is something wrong.

My python version is:

platform : win-64
conda version : 4.3.16
conda is private : False
conda-env version : 4.3.16
conda-build version : 1.21.3
python version : 3.5.2.final.0
requests version : 2.12.4

The sphinx-err-m5iglv2b.log is paste below.

# Sphinx version: 1.3.1
# Python version: 3.5.2 (CPython)
# Docutils version: 0.13.1 release
# Jinja2 version: 2.9.4
# Last messages:
#   writing output... [ 49%] py_tutorials/py_imgproc/py_geometric_transformations/py_geometric_transformations
#   writing output... [ 50%] py_tutorials/py_imgproc/py_grabcut/py_grabcut
#   writing output... [ 51%] py_tutorials/py_imgproc/py_gradients/py_gradients
#   writing output... [ 53%] py_tutorials/py_imgproc/py_histograms/py_2d_histogram/py_2d_histogram
#   writing output... [ 54%] py_tutorials/py_imgproc/py_histograms/py_histogram_backprojection/py_histogram_backprojection
#   writing output... [ 55%] py_tutorials/py_imgproc/py_histograms/py_histogram_begins/py_histogram_begins
#   writing output... [ 56%] py_tutorials/py_imgproc/py_histograms/py_histogram_equalization/py_histogram_equalization
#   writing output... [ 58%] py_tutorials/py_imgproc/py_histograms/py_table_of_contents_histograms/py_table_of_contents_histograms
#   writing output... [ 59%] py_tutorials/py_imgproc/py_houghcircles/py_houghcircles
#   writing output... [ 60%] py_tutorials/py_imgproc/py_houghlines/py_houghlines
# Loaded extensions:
#   sphinx.ext.todo (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\todo.py
#   alabaster (0.7.9) from D:\Anaconda3\lib\site-packages\alabaster\__init__.py
#   sphinx.ext.doctest (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\doctest.py
#   sphinx.ext.coverage (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\coverage.py
#   sphinx.ext.pngmath (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\pngmath.py
#   sphinx.ext.extlinks (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\extlinks.py
#   sphinx.ext.autodoc (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\autodoc.py
#   sphinx.ext.intersphinx (1.3.1) from D:\Anaconda3\lib\site-packages\sphinx\ext\intersphinx.py
Traceback (most recent call last):
  File "D:\Anaconda3\lib\site-packages\sphinx\cmdline.py", line 245, in main
    app.build(opts.force_all, filenames)
  File "D:\Anaconda3\lib\site-packages\sphinx\application.py", line 264, in build
    self.builder.build_update()
  File "D:\Anaconda3\lib\site-packages\sphinx\builders\__init__.py", line 245, in build_update
    'out of date' % len(to_build))
  File "D:\Anaconda3\lib\site-packages\sphinx\builders\__init__.py", line 316, in build
    self.write(docnames, list(updated_docnames), method)
  File "D:\Anaconda3\lib\site-packages\sphinx\builders\__init__.py", line 354, in write
    self._write_serial(sorted(docnames), warnings)
  File "D:\Anaconda3\lib\site-packages\sphinx\builders\__init__.py", line 362, in _write_serial
    self.write_doc(docname, doctree)
  File "D:\Anaconda3\lib\site-packages\sphinx\builders\html.py", line 439, in write_doc
    self.docwriter.write(doctree, destination)
  File "D:\Anaconda3\lib\site-packages\docutils\writers\__init__.py", line 80, in write
    self.translate()
  File "D:\Anaconda3\lib\site-packages\sphinx\writers\html.py", line 53, in translate
    self.document.walkabout(visitor)
  File "D:\Anaconda3\lib\site-packages\docutils\nodes.py", line 187, in walkabout
    visitor.dispatch_departure(self)
  File "D:\Anaconda3\lib\site-packages\docutils\nodes.py", line 1895, in dispatch_departure
    return method(node)
  File "D:\Anaconda3\lib\site-packages\docutils\writers\_html_base.py", line 671, in depart_document
    assert not self.context, 'len(context) = %s' % len(self.context)
AssertionError: len(context) = 1

Sample code doesn't run: OpenCV Error: Assertion failed (ni > 0 && ni == ni1) in collectCalibrationData

Code from https://github.com/abidrahmank/OpenCV2-Python-Tutorials/blob/master/source/py_tutorials/py_calib3d/py_calibration/py_calibration.rst fails to run

import numpy as np
import cv2
import glob

# termination criteria
criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001)

# prepare object points, like (0,0,0), (1,0,0), (2,0,0) ....,(6,5,0)
objp = np.zeros((6*7,3), np.float32)
objp[:,:2] = np.mgrid[0:7,0:6].T.reshape(-1,2)

# Arrays to store object points and image points from all the images.
objpoints = [] # 3d point in real world space
imgpoints = [] # 2d points in image plane.

images = glob.glob('*.jpg')

for fname in images:
    print 'Filename: ', fname
    img = cv2.imread(fname)
    gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

    # Find the chess board corners
    ret, corners = cv2.findChessboardCorners(gray, (7,6),None)

    # If found, add object points, image points (after refining them)
    if ret == True:
        objpoints.append(objp)

        corners2 = cv2.cornerSubPix(gray,corners,(11,11),(-1,-1),criteria)
        imgpoints.append(corners2)

        # Draw and display the corners
        #cv2.drawChessboardCorners(img, (7,6), corners2,ret)
        #cv2.imshow('img',img)
        #cv2.waitKey(500)

print 'Objects points: {0}, image points: {1}'.format(objpoints, imgpoints)
ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1])#,None,None)

cv2.destroyAllWindows()

OpenCV Error: Assertion failed (ni > 0 && ni == ni1) in collectCalibrationData, file /tmp/opencv20160107-29960-t5glvv/opencv-2.4.12/modules/calib3d/src/calibration.cpp, line 3193
Traceback (most recent call last):
  File "calib.py", line 39, in <module>
    ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1])#,None,None)
cv2.error: /tmp/opencv20160107-29960-t5glvv/opencv-2.4.12/modules/calib3d/src/calibration.cpp:3193: error: (-215) ni > 0 && ni == ni1 in function collectCalibrationData

Read the Docs URL

Hey, I just stumbled over your documentation on Read the Docs.
I think I've spotted a typo in the URL: opencv-python-tutroals.readthedocs.org

Shouldn't it be opencv-python-tutorials.readthedocs.org ?

Nice regards

matching features in same image

can you tell me how to how can I matching SIFT features in same image in order to detect copy move forgery detection

the mean_error not assign value in Re-projection Error section in Camera Calibration

mean_error = 0
for i in xrange(len(objpoints)):
imgpoints2, _ = cv2.projectPoints(objpoints[i], rvecs[i], tvecs[i], mtx, dist)
error = cv2.norm(imgpoints[i],imgpoints2, cv2.NORM_L2)/len(imgpoints2)
tot_error += error

print "total error: ", mean_error/len(objpoints)

it should be :

mean_error = 0
tot_error = 0
for i in xrange(len(objpoints)):
imgpoints2, _ = cv2.projectPoints(objpoints[i], rvecs[i], tvecs[i], mtx, dist)
error = cv2.norm(imgpoints[i], imgpoints2, cv2.NORM_L2) / len(imgpoints2)
tot_error += error
mean_error = tot_error / len(objpoints)
print "mean error: ", mean_error
print "total error: ", tot_error

In complex illumination environment, is there any more robust algorithm to correct, the traditional image processing algorithm is not robust, please recommend?

AttributeError: 'module' object has no attribute 'SIFT'

The code:

import cv2
import numpy as np

img = cv2.imread('home.jpg')
gray= cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

sift = cv2.SIFT()
kp = sift.detect(gray,None)

img=cv2.drawKeypoints(gray,kp)

cv2.imwrite('sift_keypoints.jpg',img)

The error:
AttributeError: 'module' object has no attribute 'SIFT'

How can the calibrated data be saved as npz?

Regarding arguments of cv2.drawContours()

Can you please what is significance of every parameters of cv2.drawContours() in readme .

Fast fourier transform example is wrong : ringing effect detected

In this path:

OpenCV2-Python-Tutorials/source/py_tutorials/py_imgproc/py_transforms/py_fourier_transform/py_fourier_transform.rst

There is an example that explains how to apply a filter in the frequency domain but there is an error, the filter MUST be transformed with FFT before multiplying it with the image to eliminate the ringing effect. I'm working on that, but if anyone knows how to do it, please fix that example.

Pyramid example: negative Laplacian results are being saturated to zero.

A minor problem in source/py_tutorials/py_imgproc/py_pyramids/py_pyramids.rst

The laplacians are being generated with
L = cv2.subtract(gpA[i-1],GE)

... however the datatype is 'uint8' so results which should be negative are being clipped to zero. As a result the reconstruction fails: this is clear by comparing the left and right parts of the result (away from the transition) to the original images - they should be the same as the original, but are brighter and less sharp (as if a haze has been added) due to loss of the negative Laplacian terms.

It can fixed by working in int16:

# generate Gaussian pyramid for A
G = A.astype('int16')   
...
G = B.astype('int16')   

( instead of A.copy().. )

... which gives the proper result.

It's also possible to improve the the illustration by doing a simple blend (across one or two pixels) instead of just concatenating - at each level of the pyramid before reconstruction. Such a change improves the 'normal' output example just a little bit, and improves the pyramid-blended version substantially, by generating a much longer effective cross-blend in the lower pyramid layers. Though it may overcomplicate the example.

img = cv2.line(img, ...) vs. cv2.line(img, ...)

Hi,

I'm running through the OpenCV Drawing Functions tutorials and this link has a series of typos for me. http://opencv-python-tutroals.readthedocs.org/en/latest/py_tutorials/py_gui/py_drawing_functions/py_drawing_functions.html#drawing-functions

For example when I run
img = cv2.line(img,(0,0),(511,511),(255,0,0),5)
then cv2.line returns None and promptly overwrites img with None.

I'm in Python 2, not Python 3. Does the functionality change going from 2 to 3? Is this a typo for other poeple as well?

Bug in the Face Detection using Haar Cascades

Hi, kindly remind that "img = cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)" should be converted into "cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)" to fix the bug "TypeError: 'NoneType' object has no attribute 'getitem'"

Syntax error in Contour Features

If you look at

http://opencv-python-tutroals.readthedocs.org/en/latest/py_tutorials/py_imgproc/py_contours/py_contour_features/py_contour_features.html#contour-features

There should be an image output in the first section

img,contours,hierarchy = cv2.findContours(thresh, 1, 2)

otherwise it doesn't work, this is correct in earlier and later sections

Checking to see why matrix of points is reshaped in Drawing Functions tutorial

Stepping through the tutorials, and I was wondering about the following line: pts = pts.reshape((-1,1,2)) in the Drawing Functions tutorial. Is there a reason it should be rows x 1 x 2 shaped and not rows x 2? When commenting out the reshape, I can see no change in the image produced so I'm curious what I'm missing. If it IS necessary, some more explanation would be lovely to have added.

Broken images in online version

hi there,

first of all many many thanks for all the great tutorial! i really appreciate it, it is such a great resource for learning openCV with python!

but unfortunately it seems that all images of the online version (https://opencv-python-tutroals.readthedocs.org/en/latest/index.html) are broken ... any chance to have them back? :)

best,
benedikt

New location (for box.jpg and box_in_scene.jpg):

New location (for box.jpg and box_in_scene.jpg):

https://github.com/opencv/opencv/tree/master/samples/data

GrabCut Mask Algorithm Not Working

I am implementing an interactive GrabCut algorithm. When I apply the masks, the area corresponding to the mask is only highlighted.

The rectangle grabcut works well.

Then I load the mask using the interactive paint. It works well too.

Here is where the problem is. Part of the image is only selected. Can you upload code of implemented grabcut through masks please.(Not in your documentation)

Needless to say, other parts of the documentation is very awesome and I highly appreciate your efforts.

py_setup_in_fedora: ffmpeg-devel not available

following the "install opencv from source tutorial" i should install the ffmeg-devel package. but the package is not available:

[jan@localhost opencv]$ sudo yum install ffmpeg-devel
Fedora Modular 30 - x86_64 75 kB/s | 24 kB 00:00
Fedora Modular 30 - x86_64 - Updates 114 kB/s | 23 kB 00:00
Fedora 30 - x86_64 - Updates 23 kB/s | 24 kB 00:01
Fedora 30 - x86_64 31 kB/s | 24 kB 00:00
Kein Treffer für Argument: ffmpeg-devel
Fehler: Es konnte kein Treffer gefunden werden.: ffmpeg-devel

A Tutorial how to install ffmpeg with opencv ?

I have searched around on google and the best I could come up with was that ffmpeg should be placed in the PATH.

But even after doing so, I am not able to play video file as per the tutorial http://docs.opencv.org/trunk/doc/py_tutorials/py_gui/py_video_display/py_video_display.html#display-video

Could do a tutorial on how to set up FFMpeg correctly ? Thanks.

Error in the camera calibration tutorial

Hi,

I believe there is an error in the code given in the camera calibration tutorial.

When trying to find the chessboard corners, the line is currently :
ret, corners = cv2.findChessboardCorners(gray, (7,6), None)

But I believe it should be
ret, corners = cv2.findChessboardCorners(gray, (7,6), objp)

Because it is objp that is added to the objpoint list. If we read the code as it is, we always add the same initialized array objp that is never modified after creation.

In any case, thanks for the tutorials, they really help me!

Readme says build folder exists

Hi,

The readme says that a build foder exists... But it does not appear to be there. only a source folder. Obviously I can still access you files but would be great to have this explained!