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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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1answer
627 views

How to warp a pixel patch to another camera

I have two cameras with rotation and translation starting from the world origin and a patch in the first camera's reference coordinate system. I want to warp this patch into the second camera's ...
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1answer
57 views

Removing lines of certain length from an image in MATLAB

I want to remove the portion of the line (highlighted by the yellow circles) where pixels form a straight vertical line segment. If I use the strel ...
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1answer
228 views

Can I segment characters from this image with CSV?

I am trying to segment my characters on this image with using column sum vector. This method actually works on the paper I've read about license plate recognition. it looks useful for my images ...
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0answers
13 views

Understanding performance of Lucas Kanade Iterative Image Registration Technique

I am reading the paper: Lucas, B. D., & Kanade, T. (1981). An iterative image registration technique with an application to stereo vision. I am having some trouble understanding section 4.3 ...
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1answer
412 views

Can you detect circles only using the hough line transform?

I'm not talking about the Hough Circle Transform (where you replace the representing eqns, hence the parameters with a 3D set) but a Hough Line Transform. My solution to this: A hough line transform ...
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2answers
60 views

Scratch Detection On Noisy Textured Surface

I wish to extract long thin scratches from the noisy background image.I have tried several ways such as stacking smoothed image with input image to remove some of the noisy background patch before ...
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1answer
219 views

Algo name: detecting elongated shape in 2d image by convolution with directed lines

I am detecting a shape with roughly known orientation (obtained by using Hough line transform) in thresholded binary image by convolving the image with line with that orientation, and counting the ...
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0answers
20 views

Disabled parking sign detection

I would like to ask you, if you could recommend some algorithm for detection of handicapped or disabled parking sign painted on the road or on the traffic sign. I am thinking about image morphology (...
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1answer
37 views

How to extract a smooth contour from a set of points in 3D?

I am trying to segment a 3D volume. The outcome of all my volume segmentation algorithms is a set of candidate points in 3D space. Now I need to smooth this point cloud and fit a closed surface it. My ...
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0answers
5 views

Sigma Value change after down-sampling

I am I have an image with a specific sigma(say 2). I downsample the image. Will thr be any change in the sigma for the downsampled image?
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1answer
37 views

How is the Gaussian kernel related to the Euclidean distance of the neighbourhoods in the non-local means algorithm?

I am reading the paper A non-local algorithm for image denoising that describes the original non-local means algorithm. They define (p. 3 of the pdf) the distance between two square fixed ...
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2answers
59 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 ...
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1answer
33 views

What is the relation between time, frequency, spatial and spectral domains?

What is the relation between time, frequency, spatial and spectral domains? I think that time and spatial domains are the "original" domains (e.g. if the signal is a greyscale image, then the domain ...
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1answer
107 views

Image reconstruction using Irradiation

I am a bit confused as to how to go about this. I have a surface [x,y,z] given by: ...
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2answers
73 views

Why isn't bilateral filtering shift-invariant?

I have a source (that I can't share) that states that bilateral filtering isn't shift-invariant (that is, it depends on the input signal), hence we cannot use convolution and the Fourier convolution ...
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1answer
25 views

What is energy in image processing?

There are several web articles on the topic, but, after having read them, I still don't know what "energy" is, in the context of computer vision (CV) and image processing (IP). It is related to ...
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0answers
12 views

Use FOV or camera deprojection to find position of pixel in world coordinates relative to my camera?

A teammate and I were discussing how best to get a 3D coordinate point (X, Y, Z) in world units from an RGB-D depth image. I'm using an intel real sense D435. From how I have researched it using the ...
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3answers
82 views

How Much Zero Padding Do We Need to Perform Filtering in the Fourier Domain?

Consider an $M\times N$ image $f$ and an $G \times K$ filter $h$. Given that convolution in the spatial domain corresponds to multiplication in the Fourier domain, then we can perform a convolution of ...
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1answer
26 views

Deriving vector paths from pen strokes

I want to calculate vector paths that approximate pen strokes from handwritten documents. My tool needs to run in batch mode, unlike hand tracing or Illustrator's "Image Trace" feature. The potrace ...
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1answer
32 views

What is a periodic signal in image processing?

In the context of image processing (and computer vision), the concept of convolution comes up a lot. Convolution is quite related to the concept of Fourier transform and DFT. In the context of image ...
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1answer
25 views

What is the difference between domain and range filtering?

In the context of image processing, I have heard the expressions "domain filtering" and "range filtering". What do these terms refer to? What is the difference between them?
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1answer
32 views

What are the parameters of a calibrated spherical camera?

I'm aware if we have a pinhole camera model several parameters describe the specific camera (such as aspect-ratio, focal length, principal point, distortion parameters etc). There're standard ...
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2answers
44 views

Understanding of Histogram-of-Oriented-Gradients

I am learning about HOG and I understand it from here. A well-explained page with an example. I am not understanding this concept that how it works A 16×16 block has 4 histograms which can be ...
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0answers
20 views

What is the difference between a range filter and a low-pass filter?

A low-pass filter attenuates the high frequencies, preserving only smooth variations in the provided image. The result of an image which is low-pass filtered is an image with blurred edges (hence ...
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1answer
129 views

How to Detect a Inhomogeneity Region in Image

I have an image that includes object and background. However, the object appears some inhomogeneity region due to illumination. My work is that how to detect inhomogeneity region. Which is feature can ...
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0answers
15 views

What is the relation between smoothing and blurring?

Is there any difference between smoothing and blurring? Are these two operations the same or do these terms refer to different operations?
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1answer
25 views

Why exactly is the Guassian filter a low-pass filter?

In image processing, a Guassian filter is used to blur an image. A low-pass filter is a filter that attenuates the high frequencies, preserving only smooth variations in the provided image. Is a ...
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0answers
8 views

What is intuitively a diffusion in the context of images?

I have heard the word "diffusion" in the context of image processing and computer vision. However, images are discrete and I associate the word "diffusion" with a continuous process. Intuitively, what ...
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0answers
28 views

Intuitively, why is the comb function the sampling function?

The comb function can be used to sample a continuous signal. The comb function is defined as follows $$ C_T(t) = \sum_{k=-\infty}^{\infty} \delta(t - kT) $$ where $\delta$ is the Dirac function, ...
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1answer
59 views

What do we mean by spectrum?

Consider the context of image processing and computer vision, and, in particular, discrete Fourier transform. For example, in the sentence In the Discrete Time Fourier Transform the forward ...
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0answers
29 views

What is the difference between an impulse response and a kernel?

It seems to me they are two terms used to refer to the same concept, but, according to the Wikipedia page on Guassian filter a Gaussian filter is a filter whose impulse response is a Gaussian ...
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2answers
1k views

Why do we need 4 points for homography but 7/8 points for fundamental matrix calculation?

Sorry if this is a trivial question but I could not find a suitable answer elsewhere. I recently learned about homography and fundamental matrices in a CV class. I understand how these matrices are ...
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2answers
706 views

What Does Normalizing Gradient Means?

Since my algorithm needs to detect long, coherent edges, the estimated local magnitude P for each pixel is normalized with respect to the magnitudes in it’s local neighborhood W (i.e., a 5x5 window). ...
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0answers
23 views

How does phase relate to motions in an image?

There is lots of research based on exaggerating motions by decomposing an image into complex sub-bands using pyramid representations such as the complex steerable pyramid and manipulating phase ...
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1answer
165 views

How to apply the provided wave transforms on an image

I want to implement one of the following mappings in MATLAB and verify its performance on an image, but I couldn't. Please help me with the implementation
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0answers
13 views

fitting lines based on image content with python

I trained an algorithm for road semantic segmentation that gives an output like this: I want to retrieve the coordinates of the vanishing point (the top of the triangle) and to fit two lines ...
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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
46 views

Nyquist frequency , sampling distance

I have few questions I tried to solve regarding nyquist theorem, and I would like to see your opinion if I'm doing it correctly?(one I know the answer second one not sure). 1.Let $f(x)$ and $g(x)$ be ...
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1answer
25 views

Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
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2answers
70 views

Nyquist sampling

I know that if $f_\mathrm{m}$ is the "Nyquist frequency" (max frequency) and $f_\mathrm{s}$ sampling rate then $f_\mathrm{s}>2f_\mathrm{m}$. Am I correct so far? I have a signal $x(t)$ with max ...
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0answers
59 views

tensor flow is slow on gpu

I'm trying to do people detection using tensorflow. Here is a video of what I came up for https://youtu.be/93XOujVi-1U My questions. I run the tensorflow on GPU 1050ti nvidia, and it's extremly ...
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1answer
465 views

How can I detect pipeline cracks using OpenCV and Python?

I have developed a robot that captures images of the pipeline interior as it moves. The requirement was to be able to detect cracks inside. So far i tried several OpenCV codes that find the crack ...
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0answers
29 views

Rotation invariant vs rotation variant

I have a very basic question. We have Rotation invariant filters and filters which are not invariant to rotation. Now let us suppose I want to apply one of these filters. How can I decide which one is ...
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0answers
33 views

How to normalise data for iterative computation of extrinsic camera matrix?

Hartley & Zisserman defend that data normalisation is an essential step prior to the estimation of geometric image transformations. The reasoning behind this, as stated in their book [1, Section 4....
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1answer
875 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 ...
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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): ...
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0answers
24 views

Implementation of PCA for hyper-spectral Image Processing

I have been studying the concept of PCA and its implementation for dimensionality reduction for more than 1 month. My goal is to classify a hyperspectral image using sparse representation by the ...
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0answers
12 views

How to receive v-chip signals from digital TV stream

I'm trying to retrieve and decode V-chip data from my TV streams (NTSC/ATSC digital streams). Apparently these data are embedded somewhere in the stream itself, but I have no clue how they are ...
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0answers
25 views

Co-prediction of signals

Is there any plausible method to estimate or predict one signal, on the basis of known value of another signal, provided the two signals bear a strong correlation? For instance, the audio amplitude ...
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1answer
144 views

python: how to compute the gray level histogram features as mentioned in the paper, and

Hi I am extracting the grey level features of image mentioned in this paper (part 4.5 low level features). "We describe two low level features that are particu- larly important for photo quality ...