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.
71
questions
21
votes
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 ...
45
votes
3answers
20k 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?
65
votes
4answers
48k views
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://...
47
votes
6answers
19k 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 ...
52
votes
10answers
15k 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 ...
33
votes
2answers
15k 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 ...
64
votes
9answers
74k 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?
26
votes
4answers
2k 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 ...
30
votes
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 ...
40
votes
1answer
13k 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 ...
34
votes
7answers
18k 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 ...
26
votes
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 ...
17
votes
4answers
8k 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 $...
12
votes
2answers
521 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. ...
7
votes
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
439 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?...
1
vote
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 ...
0
votes
2answers
2k 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 ...
46
votes
5answers
8k 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 ...
16
votes
2answers
19k 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 ...
17
votes
3answers
7k views
How to Detect Gradients and Edges 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 ...
28
votes
5answers
16k 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).
...
16
votes
5answers
16k 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-...
12
votes
4answers
17k 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 ...
8
votes
3answers
16k 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 ...
7
votes
1answer
17k 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 ...
14
votes
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 ...
14
votes
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 ...
14
votes
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 ...
12
votes
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 (...
8
votes
5answers
436 views
Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features
I have a task at hand where I need to detect angle of an image like the following sample (part of microchip photograph). The image does contain orthogonal features, but they could have different size, ...
7
votes
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 ...
4
votes
3answers
999 views
Resources for an introduction to computer vision
Does anyone have any suggestions on good resources or sites for learning about computer vision?
26
votes
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 ...
17
votes
2answers
11k 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
votes
1answer
934 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 ...
10
votes
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 ...
10
votes
1answer
24k 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 ...
0
votes
2answers
184 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 ...
8
votes
2answers
3k views
Generate the Convolution Matrix of 2D Kernel for Convolution Shape of `same`
I want to find a convolution matrix for a certain 2D kernel $ H $.
For example, for image Img of size $ m \times n $ , I want (in MATALB):
...
4
votes
2answers
4k 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
votes
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 ...
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 ...
1
vote
2answers
421 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 ...
9
votes
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 ...
2
votes
2answers
5k 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 ...
2
votes
1answer
138 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 ...
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
2answers
488 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
2answers
104 views
Why can convolution only be applied to compute the output of a linear filter?
We apparently cannot compute the output of a bilateral filter (BF) using convolution (with the image) because the BF is a non-linear filter. In general, why can convolution only be applied to compute ...
