Questions tagged [opencv]
OpenCV (Open Source Computer Vision) is a library for real time computer vision. When using this tag, please add a language specific tag (python, c++, ...), if relevant.
73,530
questions
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Image Processing: Algorithm Improvement for 'Coca-Cola Can' Recognition
One of the most interesting projects I've worked on in the past couple of years was a project about image processing. The goal was to develop a system to be able to recognize Coca-Cola 'cans' (note ...
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448
votes
26
answers
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Cannot find module cv2 when using OpenCV [duplicate]
I have installed OpenCV on the Occidentalis operating system (a variant of Raspbian) on a Raspberry Pi, using this script by jayrambhia. It installed version 2.4.5.
When I try import cv2 in a Python ...
- 4,513
429
votes
3
answers
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views
Simple Digit Recognition OCR in OpenCV-Python
I am trying to implement a "Digit Recognition OCR" in OpenCV-Python (cv2). It is just for learning purposes. I would like to learn both KNearest and SVM features in OpenCV.
I have 100 samples (i.e. ...
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411
votes
12
answers
1.0m
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How to crop an image in OpenCV using Python
How can I crop images, like I've done before in PIL, using OpenCV.
Working example on PIL
im = Image.open('0.png').convert('L')
im = im.crop((1, 1, 98, 33))
im.save('_0.png')
But how I can do it ...
- 4,415
395
votes
10
answers
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views
How to detect a Christmas Tree?
Which image processing techniques could be used to implement an application that detects the Christmas trees displayed in the following images?
I'm searching for solutions that are going to work ...
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314
votes
44
answers
998k
views
How do I install Python OpenCV through Conda?
I'm trying to install OpenCV for Python through Anaconda, but I can't seem to figure this out.
I tried
conda install opencv
conda install cv2
I also tried searching
conda search cv
No cigar. I ...
- 19k
261
votes
24
answers
867k
views
How do I install opencv using pip?
I need to install cv2 for a script that has been written for me. I tried pip install cv2 and pip install open_cv and got the same problem - a warning message from dist.py and complains about zlib ...
- 2,782
256
votes
14
answers
604k
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Python - Extracting and Saving Video Frames
So I've followed this tutorial but it doesn't seem to do anything. Simply nothing. It waits a few seconds and closes the program. What is wrong with this code?
import cv2
vidcap = cv2.VideoCapture('...
- 4,133
238
votes
35
answers
636k
views
ImportError: numpy.core.multiarray failed to import
I'm trying to run this program
import cv2
import time
cv.NamedWindow("camera", 1)
capture = cv.CaptureFromCAM(0)
while True:
img = cv.QueryFrame(capture)
cv.ShowImage("camera&...
user3090952
232
votes
9
answers
173k
views
Simple and fast method to compare images for similarity
I need a simple and fast way to compare two images for similarity. I.e. I want to get a high value if they contain exactly the same thing but may have some slightly different background and may be ...
- 66.8k
230
votes
12
answers
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Is there a way to detect if an image is blurry? [closed]
I was wondering if there is a way to determine if an image is blurry or not by analyzing the image data.
- 4,827
223
votes
5
answers
640k
views
How to resize an image with OpenCV2.0 and Python2.6
I want to use OpenCV2.0 and Python2.6 to show resized images. I used and adopted this example but unfortunately, this code is for OpenCV2.1 and does not seem to be working on 2.0. Here my code:
import ...
- 9,675
217
votes
6
answers
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views
How to remove convexity defects in a Sudoku square?
I was doing a fun project: Solving a Sudoku from an input image using OpenCV (as in Google goggles etc). And I have completed the task, but at the end I found a little problem for which I came here.
...
- 52.4k
205
votes
6
answers
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Checking images for similarity with OpenCV
Does OpenCV support the comparison of two images, returning some value (maybe a percentage) that indicates how similar these images are? E.g. 100% would be returned if the same image was passed twice, ...
- 8,773
202
votes
11
answers
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How to display an image
I tried to use IPython.display with the following code:
from IPython.display import display, Image
display(Image(filename='MyImage.png'))
I also tried to use matplotlib with the following code:
...
- 5,787
193
votes
6
answers
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OpenCV C++/Obj-C: Detecting a sheet of paper / Square Detection
I successfully implemented the OpenCV square-detection example in my test application, but now need to filter the output, because it's quite messy - or is my code wrong?
I'm interested in the four ...
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181
votes
2
answers
14k
views
OpenCV – Depth map from Uncalibrated Stereo System
I'm trying to get a depth map with an uncalibrated method.
I can obtain the fundamental matrix by finding correspondent points with SIFT and then using cv2.findFundamentalMat. I then use cv2....
- 3,832
173
votes
20
answers
341k
views
cv2.imshow command doesn't work properly in opencv-python
I'm using opencv 2.4.2, python 2.7
The following simple code created a window of the correct name, but its content is just blank and doesn't show the image:
import cv2
img=cv2.imread('C:/Python27/...
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171
votes
5
answers
281k
views
Convert image from PIL to openCV format
I'm trying to convert image from PIL to OpenCV format. I'm using OpenCV 2.4.3.
here is what I've attempted till now.
>>> from PIL import Image
>>> import cv2 as cv
>>> pimg =...
- 3,915
169
votes
10
answers
132k
views
Extracting text OpenCV
I am trying to find the bounding boxes of text in an image and am currently using this approach:
// calculate the local variances of the grayscale image
Mat t_mean, t_mean_2;
Mat grayF;
outImg_gray....
- 3,068
165
votes
14
answers
237k
views
OpenCV in Android Studio
I want to use OpenCV library in my app with Android Studio. I followed instructions found here but I get error
Configuration with name 'default' not found
What can be wrong?
I use Android Studio ...
- 4,441
163
votes
15
answers
483k
views
how to convert an RGB image to numpy array?
I have an RGB image. I want to convert it to numpy array. I did the following
im = cv.LoadImage("abc.tiff")
a = numpy.asarray(im)
It creates an array with no shape. I assume it is a iplimage object.
- 19k
161
votes
9
answers
281k
views
How can I sharpen an image in OpenCV?
How can I sharpen an image using OpenCV?
There are many ways of smoothing or blurring but none that I could see of sharpening.
- 5,120
157
votes
6
answers
221k
views
How to find out what type of a Mat object is with Mat::type() in OpenCV?
I am kind of confused with type() method of Mat object in OpenCV.If I have following lines:
mat = imread("C:\someimage.jpg");
type = mat.type();
and type = 16, how do I find out what type ...
- 20.5k
157
votes
26
answers
337k
views
error: (-215) !empty() in function detectMultiScale
I'm trying to learn cv2 in python 2.7, but when I run my code, in the specific part of it:
face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv2....
- 5,351
157
votes
5
answers
322k
views
Size of Matrix OpenCV
I know this might be very rudimentary, but I am new to OpenCV. Could you please tell me how to obtain the size of a matrix in OpenCV?. I googled and I am still searching, but if any of you know the ...
- 5,292
153
votes
21
answers
337k
views
Pycharm/Python OpenCV and CV2 install error [duplicate]
I've been trying to install both OpenCV and cv2 from both Pycharm and from the terminal as suggested using:
pip install --user opencv
pip install --user cv2
but I'm getting the following error for ...
- 2,361
151
votes
9
answers
172k
views
ImportError: libSM.so.6: cannot open shared object file: No such file or directory
When trying to import OpenCV, using import cv2 I get the following error:
/usr/local/lib/python2.7/dist-packages/cv2/__init__.py in <module>()
7
8 # make IDE's (PyCharm) ...
- 3,553
146
votes
3
answers
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views
Python OpenCV2 (cv2) wrapper to get image size?
How to get the size of an image in cv2 wrapper in Python OpenCV (numpy). Is there a correct way to do that other than numpy.shape(). How can I get it in these format dimensions: (width, height) list?
- 4,439
130
votes
7
answers
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views
OpenCV giving wrong color to colored images on loading
I'm loading in a color image in Python OpenCV and plotting the same. However, the image I get has it's colors all mixed up.
Here is the code:
import cv2
import numpy as np
from numpy import array, ...
- 4,156
130
votes
23
answers
611k
views
imread returns None, violating assertion !_src.empty() in function 'cvtColor' error
I am trying to do a basic colour conversion in python however I can't seem to get past the below error. I have re-installed python, opencv and tried on both python 3.4.3 (latest) and python 2.7 (which ...
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130
votes
24
answers
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ImportError: DLL load failed: %1 is not a valid Win32 application. But the DLL's are there
I have a situation very much like the one at Error "ImportError: DLL load failed: %1 is not a valid Win32 application", but the answer there isn't working for me.
My Python code says:
import ...
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129
votes
13
answers
343k
views
OpenCV & Python - Image too big to display
I have an image that is 6400 × 3200, while my screen is 1280 x 800. Therefore, the image needs to be resized for display only. I am using Python and OpenCV 2.4.9.
According to OpenCV Documentation,
...
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124
votes
21
answers
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views
RuntimeError: module compiled against API version a but this version of numpy is 9
Code:
import numpy as np
import cv
Console:
>>> runfile('/Users/isaiahnields/.spyder2/temp.py', wdir='/Users/isaiahnields/.spyder2')
RuntimeError: module compiled against API version a but ...
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120
votes
4
answers
296k
views
OpenCV: draw a rectangle around a region
How can I use OpenCV in Python to draw rectangles around some regions within an image for object detection purposes?
- 12.6k
118
votes
10
answers
336k
views
Choosing the correct upper and lower HSV boundaries for color detection with`cv::inRange` (OpenCV)
I have an image of a coffee can with an orange lid position of which I want to find.
Here is it .
gcolor2 utility shows HSV at the center of the lid to be (22, 59, 100).
The question is how to choose ...
- 1,383
116
votes
2
answers
85k
views
Should I use libc++ or libstdc++? [closed]
I am developing command line interface executables for both osx and linux using c/c++. The project will link against opencv. Should I use libc++ or libstdc++?
- 3,760
114
votes
5
answers
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How to know total number of Frame in a file with cv2 in python
How to know total number of Frame in a file ( .avi) through Python using open cv module.
If possible what all the information (resolution, fps,duration,etc) we can get of a video file through this.
- 1,181
114
votes
5
answers
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How does one convert a grayscale image to RGB in OpenCV (Python)?
I'm learning image processing using OpenCV for a realtime application. I did some thresholding on an image and want to label the contours in green, but they aren't showing up in green because my image ...
- 8,595
113
votes
8
answers
63k
views
Algorithm to detect corners of paper sheet in photo
What is the best way to detect the corners of an invoice/receipt/sheet-of-paper in a photo? This is to be used for subsequent perspective correction, before OCR.
My current approach has been:
RGB > ...
- 1,524
112
votes
9
answers
297k
views
How to write text on a image in windows using python opencv2
I want to put some text on an Image.
I am writing the code as:
cv2.putText(image,"Hello World!!!", (x,y), cv2.CV_FONT_HERSHEY_SIMPLEX, 2, 255)
It gives ERROR, saying 'module' object has no attribute ...
- 1,231
110
votes
7
answers
316k
views
inverting image in Python with OpenCV
I want to load a color image, convert it to grayscale, and then invert the data in the file.
What I need: to iterate over the array in OpenCV and change every single value with this formula (it ...
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110
votes
4
answers
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views
OpenCV Point(x,y) represent (column,row) or (row,column)
I have a 300x200 image in a Matrix src. I am applying the following operation on the image.
for(int i=0;i<src.rows;i++){
for(int j=0;j<src.cols;j++){
line( src, Point(i,j),Point(i,j), ...
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109
votes
6
answers
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Automatic contrast and brightness adjustment of a color photo of a sheet of paper with OpenCV
When photographing a sheet of paper (e.g. with phone camera), I get the following result (left image) (jpg download here). The desired result (processed manually with an image editing software) is on ...
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107
votes
5
answers
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views
Setting Camera Parameters in OpenCV/Python
I am using OpenCV (2.4) and Python (2.7.3) with a USB camera from Thorlabs (DC1545M).
I am doing some image analysis on a video stream and I would like to be able to change some of the camera ...
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104
votes
5
answers
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views
ConvergenceWarning: Liblinear failed to converge, increase the number of iterations
Running the code of linear binary pattern for Adrian. This program runs but gives the following warning:
C:\Python27\lib\site-packages\sklearn\svm\base.py:922: ConvergenceWarning: Liblinear failed ...
- 1,061
104
votes
6
answers
202k
views
OpenCV imshow doesn't need convert from BGR to RGB
As I'm lead to believe, OpenCV reads images in BGR colorspace ordering and we usually have to convert it back to RGB like this:
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
But when I try to simply ...
- 2,497
103
votes
12
answers
182k
views
What's 0xFF for in cv2.waitKey(1)?
I'm trying understand what 0xFF does under the hood in the following code snippet:
if cv2.waitKey(0) & 0xFF == ord('q'):
break
Any ideas?
- 1,183
103
votes
9
answers
202k
views
What does OpenCV's cvWaitKey( ) function do?
What happens during the execution of cvWaitKey()? What are some typical use cases? I saw it in OpenCV reference but the documentation isn't clear on its exact purpose.
- 48.3k
102
votes
12
answers
219k
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OpenCV Python rotate image by X degrees around specific point
I'm having a hard time finding examples for rotating an image around a specific point by a specific (often very small) angle in Python using OpenCV.
This is what I have so far, but it produces a very ...
- 1,017