Share Your Experience: Take the 2024 Developer Survey

# Questions tagged [opencv]

OpenCV (Open Source Computer Vision) is a cross-platform library of programming functions for real time computer vision.

359 questions
Filter by
Sorted by
Tagged with
27k views

### Finding squares in Image

I need to find the squares in an image using OpenCV (no problem in matlab or any other, generally what i expect are some ideas). Consider the test image below : I need to find those coloured squares ...
• 2,377
5k views

### Mathematics of Harris corner point detection

This is the mathematical expression for Harris corner detection: But I have the following doubts: What is the physical significance of $u$ and $v$? Many references say it is the magnitude by which ...
37k views

### How do I get the most accurate camera calibration?

First off, I hope this is the correct Stack Exchange board. My apologies if it is not. I am working on something that requires me to calibrate the camera. I have successfully implemented the code to ...
• 453
43k views

### What Is the Difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat Wavelet?

There are three techniques used in CV that seem very similar to each other, but with subtle differences: Laplacian of Gaussian: $\nabla^2\left[g(x,y,t)\ast f(x,y)\right]$ Difference of Gaussians: \$ \...
• 378
25k views

### Why do we use keypoint descriptors?

I just studied about SURF and I'm going for its implementation, but I still didn't understand why we use descriptors. I understand what keypoints are and their purpose, but when we extract the ...
• 601
76k views

### OpenCV/C++ connect nearby contours based on distance between them

I have to connect nearby contours in an image based on the distance between them which specifies if the contours are to be connected. Now there's a question already on the same problem here https://...
• 453
8k views

### People detection from above

I am trying to find some method to detect people using only one camera 3 meters above the ground. This is a frame returned by camera: UPDATE: Video test -> http://dl.dropbox.com/u/5576334/...
• 271
5k views

### How to recognize hexagonal tiling in boardgame?

I would like to recognize the boundaries of a hexagonal tiling in a photograph, like in image below: It seems to me, that a standard approach at a square grid is to first detect corners (e.g. canny)...
• 450
26k views

### How to compute camera pose from Homography matrix?

Say I use only one calibrated camera. From this camera, I get images A and B. I know the homography between A and B, computed through OpenCV's findHomography(). I know the pose (rotation matrix R and ...
• 1,049
5k views

### Image segmentation issue of different materials

Hi CV/Pattern Recognition Community, I've got a serious problem regarding the segmentation of an image. The scenario is an atmosphere within a furnace which makes my head go insane. And I need to ...
24k views

### Scale and Rotation invariant Template Matching

I'm looking for a method for scale and rotation invariant Template matching. I already tried some, but they didn't work so good for my examples or took for ever to execute . SIFT and SURF Feature ...
5k views

### Slicing and Recognition of book title and author from bookshelf image

I am trying, for my own learning purposes, to develop an implementation of an algorithm that would list books, given an image of a bookshelf like the following: The first step is to slice the image ...
• 241
9k views

### Calculating a homography based on detected lines

I know you can calculate homographies from image to camera plane using correspondence points between a "perfect model" and the image points. I'm doing it for a football pitch/field, and have used ...
5k views

### Pedestrian counting algorithm

Currently I am developing a pedestrian counter project (using OpenCV+QT on Linux). My idea about the approach is: Capture Frames Do Background Subtraction clear noises (erode, dilate) find blobs (...
• 223
24k views

### How does OpenCV find chessboard corners?

What are the internal workings of the OpenCV function findChessboardCorners?
• 1,371
3k views

### how to detect center of a blurry circle with opencv

I have got the following image: There are curvs on the picture. i would like to find center of the circles containing curves. i tried opencv and hough circle transform but had no results.
• 111
7k views

### Opencv calcHist and calcBackProject in plain english

i've started experimenting with c++ and opencv because of i want to learn image processing. Now, my first exercise is to create a skin detector with calcHist and calcBackProject. But i don't ...
• 924
351 views

### Recover curves from noisy collection of points

Background: I'm trying to make a system that tracks a number of bubbles in a video I'm implementing the bubble detection in the single image case using the Circular Hough Transform. Due to occlusion, ...
• 113
5k views

### Isolate the non blurred part of foucsed image

I have an image taken by a mobile phone camera with focus on a part of it let say a face or whatever. I want to know -approximately- where is the focused area. For example, a bounding box around the ...
2k views

### Noise removal in medical segmented image

Can anyone suggest methods for removing the noise (indicated inside the red square) from every where in the following image, while keeping the white lines?
• 301
3k views

### Vehicle counting from a video

Disclaimer: I posted this question on StackOverFlow but learned that it is better suited here. I am a bit new to image processing so I'd like to ask you about finding the optimal solution for my ...
• 203
2k views

### How to estimate octave and size for visual features positioned at Harris corners

I am currently working with and comparing the performance of several feature detectors provided by OpenCV as basis for visual feature matching. I am using SIFT descriptors. I have accomplished ...
• 3,676
2k views

### Log-Polar DFT Based Scale-Invariant Image Registration

I'm trying to do image registration using phase correlation as described in the Reddy Chatterji paper. In my case, the images may be scaled and translated relative to each other. The algorithm for ...
• 203
3k views

### Detecting a filled glass object

I've been sent here from this question in stackoverflow, please excuse me if the question comes too specific and it's not in the manners in here:) The task is to find a glass with specific liquid in ...
• 202
3k views

### FFT for line detection

I am trying use the FFT in a different way then most people ask about. I want to be able to take a picture of a graph with regular repeating vertical lines, and to process the image to determine how ...
44k views

### Removing noisy lines from image - opencv - python

I want to process different type of image to extract actual text from noisy image .I am using open cv to do this job it is working fine but the problem is I need to set different lower threshold to ...
• 191
4k views

### Is it possible to convert from 2D to 3D form?

I have captured car positions at different frames from the video. Suppose car's(e.g.left side car which is coming towards us in the images) centroid at video frame1 is P(x1,y1) and Q(x2,y2) at video ...
• 549
11k views

### How can I detect elements of GUI using opencv?

Given a screenshot of an application, is there any way of finding GUI elements of that application using only opencv? (something like in the image) I tried to play with blending the image and other ...
• 185
3k views

### Is it possible to hack camera calibration without having access to the camera?

Many times we have a stream of video to process without access to camera. Having access to camera matrix would be beneficial for various processing techniques. Is it possible to hack camera ...
1k views

### Help in Retraining a HOG Descriptor using SVMLight

I am currently trying to count cars using OpenCV 2.4.4 with a HOG descriptor. Because a model for car detection is not available in OpenCV, I am creating my own model using SVMLight and a dataset of ...
• 201
6k views

### How to remove the noise without destroying the main edge?

I am working on a project. I want to segment a logo from a car and the picture's size is 3648*2432. The logo is selected by the red rectangle. I extracted this area and turn into gray level. The ...
• 131
10k views

### Differences between OpenCV Canny and MatLab Canny?

does anyone know why the MatLab Canny (MLC) is so different compared to the OpenCV Canny (OCC)? ML-C delivers precise and more connected edges than the OCC, but how is that possible? The reason why I ...
• 587
18k views

### Measuring the contrast of an image

For a project, I want to measure the contrast of a global image. I want to compare different images to get the image with the best contrast. I know about the Weber contrast, but I need a normalized ...
7k views

### OpenCV detectin skin colour invariant with illumination changes

I have to capture skin colour independent of illumination. I used the following criteria(using hsv and rgb) but it ain't working: ...
• 453
316 views

### Convolution involving turning each pixel value to the most represented pixel value of the neighbourhood

In order to correct gradual changes of intensities in the background of grey-scales images, I have been blurring them and then subtracting the original images from the convolved one. In some cases, I ...
260 views

### Determining Toy Helicopter Orientation From Image

I am working on developing an autonomous control system for toy IR remote-controlled helicopters (like the Syma s107, for example) using a webcam and an Arduino with some IR LEDs. I am using C++ with ...
4k views

### count blood cells

How to count blood cells in opencv? The problem is that they stick together. The example picture : Maybe pairwise geometric histogram (Geometric Histograms) suitable for matching partial circle ...
• 560
3k views

### Sequentially get the outer contour of an Edge Image

Hi CV/Pattern Recognition Community, because my last thread was concerning the segmentation as BLOB and started to getting too big, with no clear results. I would like to reconcider the last step of ...
• 587
3k views

### Jigsaw puzzle: isolating the pieces (separating "stuck" blobs)

I'm new to image processing, and I'm trying to get my feet wet. I have taken a picture of some jigsaw puzzle pieces and I want to isolate the pieces. I am using the Python SimpleCV library to do this,...
2k views

### Convolution of Two Kernels [OpenCV]

I've been completely stuck on a portion of my assignment for a few days now. After plenty of searching around, I have been unsuccessful in discovering information that leads me to the correct solution....
• 61
3k views

### What Is the Cause for Poor Results with Adaptive Thresholding?

I try to run text cleaning process based on the camera captured image. By using OpenCV adaptive threshold method with parameter ...
• 185
3k views

### How are the scaling parameters included (extracted from) an essential matrix?

An essential matrix relates corresponding points between two images assuming that a camera satisfies the pinhole camera model, and can be expressed as: $$E=K'^TFK$$ where K is the calibration and F ...
2k views

### How Could One Imitate Photoshop's Vibrance Filter with OpenCV?

Can somebody please explain how Photoshop vibrance function can use in opencv c++ ? so that I may reproduce the same effects in my application. Here is the vibrance ...
• 601
3k views

### Detect lanes from a filtered image

I am working on lane detection system and I would like some suggestions from you as to how to detect lanes from a filtered image which I got after performing certain operations. Firstly, I should ...
• 175
48k views

### How to determine range of HSV values of the image?

Is there any method to find range of hsv values of image (object) in rectangle inside big image? I mean, there is fixed size rectangle on my image(frame from camera) and i want to find range of hsv ...
17k views

### K-means for 2D point clustering in python

I have a set of points(2D) whose pixels are set and want to perform k-means on these pixels. Is clustering the 2D coordinates the right way ? If so, can that be done using any libraries in python ?
• 153
5k views

### How to get a top view using open cv?

I have a situation where i need to extract the top view of a road from the 'skewed' view I get from a cc camera located on some roadside tree. I would like to do this using OpenCV, but since I'm very ...
62k views

### Python - Normalized cross-correlation to measure similarites in 2 images

I'm trying to measure per-pixel similarities in two images (same array shape and type) using Python. In many scientific papers (like this one), normalized cross-correlation is used. Here's an image ...
3k views

### Recover myself from Dilate and Erode for noise reduction

i have obtained some skin detection map (i post below two example of detection map). but, i'm using a normal webcam and the map is noisy. Not a lot, just a bit. I think i can remove noise only with ...
• 924