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Questions tagged [computer-vision]

Computer vision includes methods of processing, analyzing, images and high-dimensional data to form high level understanding and recognition of the scene or images.

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2answers
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Step by Step Camera Pose Estimation for Visual Tracking and Planar Markers

I have been working on the topic of camera pose estimation for augmented reality and visual tracking applications for a while and I think that although there is a lot of detailed information on the ...
43
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3answers
19k views

What algorithm does Google use for its “Search By Image” site?

What is your best guess how Google Image Search works? I can upload a photo and can search for similar images. What algorithm does it use to identify similar images?
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4answers
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What are some free alternatives to SIFT/ SURF that can be used in commercial applications?

As far as I understand, both SURF and SIFT are patent protected. Are there any alternative methods that can be used in a commercial application freely? For more info on the patent check out: http://...
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6answers
17k views

Best way of segmenting veins in leaves?

I have done a lot of research and found out methods like adaptive thresholding , watershed etc that can be used of detecting veins in leaves . However thresholding isn't good as it introduces a lot of ...
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10answers
13k views

Is deep learning killing image processing/computer vision?

I'm looking forward to enroll in an MSc in Signal and Image processing, or maybe Computer Vision (I have not decided yet), and this question emerged. My concern is, since deep learning doesn't need ...
31
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2answers
14k views

What's the difference between the Hough and Radon transforms?

I'm familiar with the Radon transform from learning about CT scans, but not the Hough transform. Wikipedia says The (r,θ) plane is sometimes referred to as Hough space for the set of straight ...
60
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7answers
67k views

Why do we use the HSV colour space so often in vision and image processing?

I see the HSV colour space used all over the place: for tracking, human detection, etc... I'm wondering, why? What is it about this colour space that makes it better than using RGB?
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4answers
1k views

Find the stomata in a plant microscopy image

Here is a question for image processing experts. I am working on a difficult computer vision problem. The task is to count the stomata (marked below) in DIC microscopy images. These images are ...
29
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5answers
2k views

Detecting Trail in Forest Images

Is anyone aware of any research/papers/software for identifying a trail (as a line or point-to-point curve) in an image of a forest scene (from the perspective of the camera standing somewhere along ...
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1answer
12k views

How to flatten the image of a label on a food jar?

I'd like to take pictures of labels on a jar of food, and be able to transform them so the label is flat, with the right and left side resized to be even with the center of the image. Ideally, I'd ...
23
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3answers
1k views

How to find tennis courts in aerial imagery

I'm interested in finding all tennis courts (and other similar well defined features like basketball courts) in my county, and I have aerial imagery of good (but varying) resolution, but I'm not sure ...
11
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2answers
481 views

What methodology to use for discrimination of different (musical?) tones

I am trying to research and figure out how best to attack this problem. It straddles music processing, image processing, and signal processing, and so there are a myriad number of ways to look at it. ...
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4answers
6k views

Intuitive explanation of tracking with Kalman filters

I would much appreciate an intuitive explanation for (visual) tracking with Kalman filters. what I know: Prediction step: Dynamic system state $\mathbf x_t$: target location at time $t$ Measurement $...
7
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1answer
1k views

Suggested Preprocessing methods for OCR on Circular Images

Hello this is my sample image I am going to do real time character detection on images like that. I've tried SURF, SIFT, MSER and template matching on original image without any preprocessing. I can ...
3
votes
1answer
281 views

What does an image of Fourier Transformation of an image tell us?

First time studying image processing... I just don't understand what does fourier transformed image of an image describe? For example consider given following pictures, The first one is the image, and ...
3
votes
1answer
271 views

How to calculate particles sizes for spheric particles with overlapping and superposition? (Example image included)

I'm trying to automatically calculate particles sizes histogram for images like this one: Common threshold and segmentation doesn't seem to work. What filters and algorithms do you suggest to be used?...
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1answer
1k views

Looking for algorithm to extract line network from binary images within LabView

I would like to create a LabView VI that receives an input image and the RGB-color codes of the powerlines depicted in the image. The output should (eventually) consist of id'd polygonial connections ...
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2answers
1k views

Camera calibration and extrinsic parameters for perspective transformation

I'm working in a photogrammetry camera and laser application where I need to measure a displacement in a specific plane, this is a quick diagram of the setup: In order to get proper measurements I'm ...
43
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5answers
7k views

Point Pattern Recognition

Having two different size of sets of points (2D for simplicity) dispersed within two different size squares the question are that: 1- how to find any occurrence of the the small one through the ...
17
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3answers
7k views

How to detect gradients in images?

I want to be able to find points in images that are the centre of a radial gradient like the one shown in the left picture below. Any ideas on how I could use a Hough transform or some other computer ...
16
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2answers
18k 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 ...
26
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5answers
15k views

Good language for computer vision?

I am trying to implement a content based image retrieval system but before I do so I would like to get an overview of some programming languages suitable for this task (having good libs and such). ...
14
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5answers
14k views

Scale and Rotation invariant feature descriptors

Can you list some scale and rotational invariant feature descriptors for use in feature detection. The application is for the detection of cars and humans in video captured by a UAV, using a multi-...
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2answers
2k views

Profile Matching in a Point Cloud

A point cloud is generated using uniform random function for (x,y,z). As shown on the following figure, a flat intersecting plane (profile) is being investigated ...
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4answers
15k 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 ...
7
votes
1answer
15k views

How Hessian feature detector works?

I know about Harris corner detector, and I understand the basic idea of its second moment matrix, $$M = \left[ \begin{array}{cc} I_x^2 & I_xI_y \\ I_xI_y & I_y^2 \end{array} \right]$$, edges ...
6
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2answers
14k views

Object detection versus object recognition

I have a slight confusion differentiating between object recognition and object detection. Some people say object detection is a sub-topic of object recognition? Can someone clarify the the difference ...
13
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2answers
2k views

A (Clear) Line Between Computer Vision and Image Processing

I have been working in and learning about both Computer vision and Image processing for a few years now, and I believe that I am not a complete beginner any more. Still, after all these years, it is ...
13
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2answers
7k views

Connecting edges detected by an edge detector

I have a binary image obtained from a canny edge detector. The edges are not nicely detected in the center and I need to join them. The connection of edges is orientation and neighborhood dependent. I ...
11
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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 (...
6
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3answers
3k 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 ...
24
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8answers
2k views

Are Computer Stereo Vision techniques appropriate for sub-millimetre measurements?

I have a project where I would like to image an object and be able to derive the heights of features in this image to sub-millimetre precision (exactly how precise is still yet to be determined, but ...
15
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2answers
9k views

How does resizing an image affect the intrinsic camera matrix?

I have a camera matrix (I know both intrinsic and extrinsic parameters) known for image of size HxW. (I use this matrix for some calculations I need). I want to use a smaller image, say: $\frac{H}{2}\...
10
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3answers
3k views

Camera calibration/pin hole camera model and working out 3d position

I have a calibrated camera and have the intrinsic parameters. I also have the extrinsic parameters relative to a point (the world origin) on a planar surface in the real world. This point I have set ...
9
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1answer
865 views

The Scale Space Theory Understanding

In the scale-space theory the scale-space representation of the signal $f(x), x = (x_1, ..., x_d)$, (in case of image $d = 2$) is given as: $L(x, y; t) = g(x, y; t) * f(x, y)$ where $g(x, y; t)$ is a ...
4
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3answers
871 views

Resources for an introduction to computer vision

Does anyone have any suggestions on good resources or sites for learning about computer vision?
10
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1answer
23k views

Adaptive Thresholding for liver segmentation using Matlab

I need to segment liver from an abdominal CT image using Adaptive Thresholding. But I get the entire foreground separated from the background alone. I need only the liver part of the foreground ...
4
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2answers
3k views

Why optical flow ? why not tracking

I have a question that might be stupide ! Supposing that I try to detect object moving in a video or human action. Many works are based on optical flow computation. My question is why using OF is ...
3
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2answers
4k views

camera calibration: why chessboards?

Chessboards are very frequently used for camera calibration, this website also talks a bit about why: wiki. One of the reasons is, that chessboards define many natural interest points. Now my (very ...
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vote
2answers
334 views

Harris Corner Detection

In Harris Corner detection, is there any particular reason why this function is chosen: $R=det(M)-k*trace(M)^2$ We want to a function to evaluate how fast E(u,v) fluctuate accross different ...
0
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2answers
87 views

Selecting gradient orientation for Generalized Hough Transform while scaling and rotation is present

I am using this link to study Generalized Hough Transform. I will explain it briefly. In order to detect a shape, an R-table is created for the shape with $\phi$ indicating gradient orientation for ...
9
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1answer
2k views

Good features / algorithms for recognizing car-models in images

I have a question concerning object recognition, especially recognizing car-models! I am at the beginning of a work about identifying the same car-model in different images. At the moment I think one ...
3
votes
1answer
2k views

Wavelength filter with OpenCV

I am new to OpenCV and DSP. I want to code a filter which act like a real optical filter. When you filter the image, the output looks like shotted with a $550nm$ optical filter lens. Like a Bandpass ...
3
votes
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 ...
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2answers
4k views

Edge detection on a color image

I understand the process of using a Sobel kernel for edge detection in greyscale images. The input is a greyscale image, and the output is a greyscale image. I'm having trouble, however, figuring out ...
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2answers
357 views

Seeking segmentation methods for this light microscope image

Although I am not new to math or programming, I am a total newbie to image segmentation. I have the following light microscope image and I would like to segment it into cytoplasm (the magenta ...
1
vote
1answer
4k views

Ground plane estimation from a single image (was: confusion about homography and calibration camera parameters)

I'm new to this multiple view geometry issues and I'm a little bit lost, and some concept are not clear at all. I have a calibrated camera ( = I have distortion coefficents, field of view, and with ...
1
vote
1answer
98 views

Automatic Image Enhancement of Images of Scanned Documents (Auto Whitening)

Dropbox have make a blog post about there automatic enhancement method for scanned document image - Fast Document Rectification and Enhancement. I followed the post and they mention a formula to make ...
0
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1answer
79 views

what is $1/f$ property of the visual world?

I was watching a talk by Edward H. Adelson on the perception of materials and surfaces. He mentions a $1/f$ property of the visual world. He says: low frequencies are prevalent than high ...
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4answers
1k views

basic hsb skin detection, neon illumination

i hope this is the right place to ask. otherways sorry for my mistake and pleace advice me a better site. i'm trying to implement a super simple skin detector using some range of hsb image. i'm using ...