Questions tagged [opencv]

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

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4
votes
3answers
2k views

Vein extraction from this image

I have this image: What methods should I use to extract the veins from this image. Thank you.
23
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1answer
4k 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 ...
10
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2answers
16k 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: $ \...
0
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1answer
538 views

2D DWT Image Issue

In the literature, I see that a 2D signal can be transformed by first doing a 1D transformation on each row of the matrix followed by the same procedure on each column. It seems that $k^{th}$ level ...
34
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7answers
19k 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 ...
4
votes
1answer
4k 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 ...
18
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2answers
20k 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 ...
12
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4answers
18k 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 ...
12
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2answers
4k 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 (...
10
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2answers
4k 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 ...
7
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3answers
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 ...
8
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2answers
4k 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 ...
4
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1answer
2k views

what is the starting point of a contour as given by cvConvexityDefect() function in OpenCV

i have to distinguish between palm and elbow in my contour(I'm using cvconvexitydefect for that purpose). Here's the image: I'm taking contour of left image. the 2 topmost points in right image are ...
7
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1answer
6k 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 ...
2
votes
1answer
263 views

How to Get Rid of Ripples from a Gradient Image of a Smoothed Image?

I have a gray scale UINT8 image. When I smooth it with a Gaussian filter and then compute the gradient image with a Sobel filter in OpenCV, ripples would appear. ...
5
votes
2answers
2k 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 ...
5
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3answers
2k views

How to remove text region in a document image? or extract image from a document image

Given a document image (i.e. newspaper), how to extract photos in it or remove text region? I think traditional OCR methods may not be suitable here, as I don't need to recognize the text, and OCR is ...
4
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1answer
753 views

Feature Detection on a Circular Metal Surface for Character Recognition

Hello I'm trying to recognize characters on the circular metal surface. Without any preprocessing I could match cropped features with original image. I've actually cropped 2 characters together to ...
3
votes
1answer
1k views

Obtain motion between image features by means of the homography matrix

I have been reading several really good answers about how to obtain camera pose (rotation, translation, etc), such as this one and this one, but I am not sure how this applies to my problem. My ...
3
votes
0answers
842 views

Optimal measurement model for Kalman in Augmented Reality

I am developing an augmented reality SDK that uses Kalman for tracking a planar marker. My state is composed of 3D position, a quaternion, velocity and angular velocity. \begin{bmatrix}{\vec{p}}\\{\...
0
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1answer
2k views

Histogram and binary image in opencv? [closed]

I would like to compute how many zeros and ones (e.i. 255) in a binary image. The following code to generate a binary image by using Matlab. ...
0
votes
1answer
375 views

python: how to compute the sharpness features of image

I am extracting the sharpness features of image as shown in the following image mentioned in a paper. I have done with the following code. Firstly, use the open cv convert the RGB to HSL (luminance ...