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c++opencv
1910 votes
23 answers
241k views

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 ...
Charles Menguy's user avatar
395 votes
10 answers
26k 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 ...
karlphillip's user avatar
  • 92.8k
193 votes
6 answers
133k views

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 ...
dom's user avatar
  • 12k
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....
Clip's user avatar
  • 3,068
110 votes
4 answers
137k 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), ...
user3747190's user avatar
  • 1,687
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.
Simplicity's user avatar
  • 48.3k
96 votes
5 answers
92k views

Does performance differ between Python or C++ coding of OpenCV?

I aim to start opencv little by little but first I need to decide which API of OpenCV is more useful. I predict that Python implementation is shorter but running time will be more dense and slow ...
erogol's user avatar
  • 13.4k
84 votes
2 answers
206k views

How to get image width and height in OpenCV? [duplicate]

I want to get image width and height, how can I do that in OpenCV? For example: Mat src = imread("path_to_image"); cout << src.width; Is that right?
sarmad m's user avatar
  • 889
83 votes
6 answers
159k views

Accessing certain pixel RGB value in openCV

I have searched internet and stackoverflow thoroughly, but I haven't found answer to my question: How can I get/set (both) RGB value of certain (given by x,y coordinates) pixel in OpenCV? What's ...
Wookie88's user avatar
  • 34k
73 votes
2 answers
122k views

What are the differences between CV_8U and CV_32F and what should I worry about when converting between them?

I have some code that is acting up and I suspect it's because I'm operating on the wrong types of data or converting between them poorly. It is mixing cv::Mat objects of types CV_8U (which is what ...
mic's user avatar
  • 733
73 votes
3 answers
101k views

What does CV_8UC3 and the other types stand for in OpenCV?

I was surprised when I couldn't find anything in OpenCV documentation describing - with words - what the various types stand for, and Googling wasn't much help either. I know that CV_8UC1 is gray-...
sashoalm's user avatar
  • 77.3k
72 votes
2 answers
103k views

Recommended values for OpenCV detectMultiScale() parameters

What are the recommended parameters for CascadeClassifier::detectMultiScale() and depending on which factors I should change default parameters? void CascadeClassifier::detectMultiScale( const ...
torayeff's user avatar
  • 9,526
70 votes
7 answers
136k views

Easiest way to rotate by 90 degrees an image using OpenCV?

What is the best way (in c/c++) to rotate an IplImage/cv::Mat by 90 degrees? I would assume that there must be something better than transforming it using a matrix, but I can't seem to find anything ...
Ben H's user avatar
  • 3,176
70 votes
5 answers
134k views

Print out the values of a (Mat) matrix in OpenCV C++

I want to dump the values of a matrix in OpenCV to the console using cout. I quickly learned that I do not understand OpenvCV's type system nor C++ templates well enough to accomplish this simple task....
ahoffer's user avatar
  • 6,445
69 votes
5 answers
114k views

linux/videodev.h : no such file or directory - OpenCV on ubuntu 11.04

I tried to install OpenCV2.2 on Ubuntu 11.04. But OpenCV compilation fails stating an error related to linux/videodev.h file. File available in /user/includes/linux is named videodev2.h. /home/user/...
Niroshan's user avatar
  • 2,064
67 votes
13 answers
94k views

Rotate an image without cropping in OpenCV in C++

I'd like to rotate an image, but I can't obtain the rotated image without cropping My original image: Now I use this code: #include <opencv2/core/core.hpp> #include <opencv2/highgui/highgui....
Manuel Ignacio López Quintero's user avatar
67 votes
5 answers
177k views

Convert RGB to Black & White in OpenCV

I would like to know how to convert an RGB image into a black & white (binary) image. After conversion, how can I save the modified image to disk?
mohammed's user avatar
  • 867
66 votes
10 answers
170k views

Convert Mat to Array/Vector in OpenCV

I am novice in OpenCV. Recently, I have troubles finding OpenCV functions to convert from Mat to Array. I researched with .ptr and .at methods available in OpenCV APIs, but I could not get proper data....
Main's user avatar
  • 1,832
65 votes
5 answers
356k views

Find OpenCV Version Installed on Ubuntu [duplicate]

I would like to find out what version of OpenCV is installed on my computer (i am running Ubuntu 10.04). Is there a simple way to check it if ? If not then can i find out the directories where files (...
Saad's user avatar
  • 933
65 votes
2 answers
60k views

Camera position in world coordinate from cv::solvePnP

I have a calibrated camera (intrinsic matrix and distortion coefficients) and I want to know the camera position knowing some 3d points and their corresponding points in the image (2d points). I know ...
nkint's user avatar
  • 11.7k
65 votes
1 answer
4k views

OpenCV undistortPoints and triangulatePoint give odd results (stereo)

I'm trying to get 3D coordinates of several points in space, but I'm getting odd results from both undistortPoints() and triangulatePoints(). Since both cameras have different resolution, I've ...
Petersaber's user avatar
64 votes
1 answer
62k views

using OpenCV and SVM with images

I am having difficulty with reading an image, extracting features for training, and testing on new images in OpenCV using SVMs. can someone please point me to a great link? I have looked at the OpenCV ...
Carnez Davis's user avatar
64 votes
1 answer
21k views

Classification of detectors, extractors and matchers

I am new to opencv and trying to implement image matching between two images. For this purpose, I'm trying to understand the difference between feature descriptors, descriptor extractors and ...
hriddle's user avatar
  • 789
62 votes
3 answers
102k views

Copy an cv::Mat inside a ROI of another one

I need to copy a cv::Mat image (source) to an ROI of another (Destination) cv::Mat image. I found this reference, but it seems that it does not work for my case. Do you have any pointers how could I ...
theosem's user avatar
  • 1,184
61 votes
6 answers
87k views

Simple illumination correction in images OpenCV C++

I have some color photos and the illumination is not regular in the photos: one side of the image is brighter than the other side. I would like to solve this problem by correcting the illumination. I ...
user3762718's user avatar
61 votes
2 answers
32k views

Removing watermark out of an image using OpenCV

First of all I have this image and I want to make an application that can detect images like it and remove the circle (watermark) from it. int main(){ Mat im1,im2,im3,gray,gray2,result; im2=...
Ahmed Ramzy's user avatar
60 votes
1 answer
118k views

Installing OpenCV 2.4.3 in Visual C++ 2010 Express [closed]

How do you install and use OpenCV 2.4.3 under VC++ 2010 Express?
flowfree's user avatar
  • 16.5k
60 votes
8 answers
37k views

How can I determine distance from an object in a video?

I have a video file recorded from the front of a moving vehicle. I am going to use OpenCV for object detection and recognition but I'm stuck on one aspect. How can I determine the distance from a ...
Ryan R.'s user avatar
  • 816
59 votes
5 answers
156k views

openCV program compile error "libopencv_core.so.2.4: cannot open shared object file: No such file or directory" in ubuntu 12.04

I compiled and installed openCV 2.4.2 in ubuntu 12.04. Under /usr/local/include I can see the directories /usr/local/opencv and /usr/local/opencv2. Here is the code I wrote: #include <cv.h> #...
linkrules's user avatar
  • 701
59 votes
6 answers
49k views

Executing cv::warpPerspective for a fake deskewing on a set of cv::Point

I'm trying to do a perspective transformation of a set of points in order to achieve a deskewing effect: http://nuigroup.com/?ACT=28&fid=27&aid=1892_H6eNAaign4Mrnn30Au8d I'm using the image ...
karlphillip's user avatar
  • 92.8k
59 votes
5 answers
172k views

g++ ld: symbol(s) not found for architecture x86_64

I'm trying to compile the Sam Hare's Struck code. I'm using mac OSX10.9, opencv 2.4.6 and Eigen 2.0.17. Eigen and opencv headers are stored in /opt/local/include while opencv dylib in /opt/local/lib....
mbPro's user avatar
  • 757
58 votes
5 answers
80k views

opencv multi channel element access

I'm trying to learn how to use OpenCV's new C++ interface. How do I access elements of a multi channel matrix? For example: Mat myMat(size(3, 3), CV_32FC2); for (int i = 0; i < 3; ++i) { for (...
Yair's user avatar
  • 1,345
55 votes
8 answers
135k views

Converting cv::Mat to IplImage*

The documentation on this seems incredibly spotty. I've basically got an empty array of IplImage*s (IplImage** imageArray) and I'm calling a function to import an array of cv::Mats - I want to ...
amr's user avatar
  • 1,265
54 votes
4 answers
188k views

c++ and opencv get and set pixel color to Mat

I'm trying to set a new color value to some pixel into a cv::Mat image my code is below: Mat image = img; for(int y=0;y<img.rows;y++) { for(int x=0;x<img.cols;x++) { ...
grll's user avatar
  • 1,077
54 votes
6 answers
59k views

Writing robust (color and size invariant) circle detection with OpenCV (based on Hough transform or other features)

I wrote the following very simple python code to find circles in an image: import cv import numpy as np WAITKEY_DELAY_MS = 10 STOP_KEY = 'q' cv.NamedWindow("image - press 'q' to quit", cv....
memyself's user avatar
  • 12.4k
52 votes
11 answers
70k views

How to convert an OpenCV cv::Mat to QImage

I am wondering how would I convert the OpenCV C++ standard cv::Mat type to QImage. I have been searching around, but have no luck. I have found some code that converts the IPlimage to QImage, but that ...
Hien's user avatar
  • 1,769
50 votes
2 answers
106k views

How to link opencv in QtCreator and use Qt library

This question must be duplicate many times, but it just doesn't work and sometimes it still remains unanswered. Sources of information are mainly these http://www.laganiere.name/opencvCookbook/...
Daniel Katz's user avatar
  • 2,340
49 votes
2 answers
163k views

How can I convert a cv::Mat to a gray scale in OpenCv?

How can I convert a cv::Mat to a gray scale? I am trying to run drawKeyPoints func from opencv, however I have been getting an Assertion Filed error. My guess is that it needs to receive a gray scale ...
user1319603's user avatar
49 votes
2 answers
197k views

How to solve munmap_chunk(): invalid pointer error in C++

I have an application in C++ and OpenCV which tries to use the classification model realized with SVMLight in order to add the weight values which can be use for HOG Calssificator under OpenCV. The ...
Marcus Barnet's user avatar
48 votes
1 answer
66k views

Installing C++ Libraries on OS X

I am trying to get my head around some basic concepts, but I can't seem to figure them out. I am really confused over what it means to install (I think they are called libraries) for C++. I am ...
Giesbrecht's user avatar
46 votes
5 answers
60k views

How to correctly use cv::triangulatePoints()

I am trying to triangulate some points with OpenCV and I found this cv::triangulatePoints() function. The problem is that there is almost no documentation or examples of it. I have some doubts about ...
Ander Biguri's user avatar
  • 35.4k
46 votes
4 answers
6k views

Extracting segments from a list of 8-connected pixels

Current situation: I'm trying to extract segments from an image. Thanks to openCV's findContours() method, I now have a list of 8-connected point for every contours. However, these lists are not ...
B. Decoster's user avatar
  • 7,783
45 votes
9 answers
121k views

How to calculate the angle from rotation matrix

I am using two image of the single object the object is roated certain degree from its first image. I have calculated the POSE of each image and converted the rotational vector to Matrix using ...
N.J's user avatar
  • 1,210
45 votes
11 answers
68k views

Shift image content with OpenCV

Starting from an image, I would like to shift its content upward of 10 pixels, without changing size and filling in black the sub image (width x 10px) on the bottom. For instance, the original: And ...
vdenotaris's user avatar
  • 13.5k
45 votes
2 answers
100k views

Compiling a static executable with CMake

for a project I need to create an executable that includes all the libraries that I used (opencv, cgal) in order to execute it on a computer that has not those libraries. Currently, this is my ...
Andrea's user avatar
  • 1,639
45 votes
1 answer
110k views

cmake find_package specify path

I have 2 versions of OpenCV installed on my machine. One is in /usr/local/opencv3.1. I presume the install location of the other one (version 3.4) is /usr/local. Anyway, find_package(OpenCV 3.0 ...
Gerry's user avatar
  • 2,030
44 votes
3 answers
210k views

OpenCV get pixel channel value from Mat image

Maybe I'm not looking hard enough, but everything seems to want me to use an array. Thus, how do I get the channel value for a particular pixel for foo if foo is something like Mat foo = imread("bar....
HRÓÐÓLFR's user avatar
  • 5,952
43 votes
6 answers
75k views

connected components in OpenCV

I am looking for an OpenCV function that can find connected components and perform a few tasks on them ( like getting the number of pixels, contour, list of pixels in the object etc.. ) Is there a ...
EyalG's user avatar
  • 1,223
42 votes
10 answers
52k views

how to check whether two matrices are identical in OpenCV

I have two instances of cv::Mat : m1 and m2. They are of the same numeric type and sizes. Is there any function in OpenCV that returns whether the matrices are identical (have all the same values)?
kirkor's user avatar
  • 421
42 votes
2 answers
144k views

Resize image OpenCV

If I have an image called inImg and an image named outImg how can I resize outImg so that it is 75% the size of inImg?
Clip's user avatar
  • 3,068

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