Questions tagged [image-processing]
In general, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame.
2,337
questions
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7 views
Size filtering on binary images
I have noisy images from which I extract the contours using OpencCV's findCountours, which performs binarization internally. This results in innumerable small ...
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1answer
12 views
What is the difference between positive matrix coefficients and negative matrix coefficients of an audio?
I have turned an audio file into an one dimensional array by using audioread function in matlab and found several positive and negative fractional coefficient values.What is the basic difference of ...
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1answer
28 views
How can I detect the tree rings?
I'm looking for the way to detect the tree rings automatically in the wood dist image.
Using the matlab, I have removed the background, and binarized the image.
How can I detect the white and black ...
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0answers
8 views
Questions about Optical Flow implementations
I have some doubts related to some of the optical flow implementations.
How to compute angular error for optical flow algorithms? I know the formula for computing,
$\theta=\arccos(\vec{v}_c\cdot\vec{...
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0answers
11 views
Extract feature points and visualize on 3d Mesh
I'm Coding with python,
I have a 3d Model mesh, and I'm trying to get features and descriptors
So I was able to get Zernike moments using mahotas library which gives a vector of data, I have to ...
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0answers
10 views
What is the name and theory behind a basic motion filter with background update?
I am working on machine vision task. I am using openCV in Python. I need to detect motion. Best would be if I can calculate the difference between the new image and background. However, the ...
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0answers
4 views
can I combine 2 raster with wavelet transform in R?
I Have same problem, i will combine 2 raster data with wavelet fusion
r1<-brick("mask data/r1_mask_black.tif")
r2<-brick("mask data/r2_mask_black.tif")
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0answers
18 views
Detect Colors in an image using opencv python
How to find different colors present in an image? Is K means clustering enough or any other simple way of doing it using opencv exist?
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0answers
12 views
Kalman Filter in Vision - Constant Velocity Model - Units
Let's assume we have series of frames with a known object. I want to track the object using Kalman filter using constant velocity / acceleration models. My questions are:
(i) Which model to use? CV ...
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0answers
26 views
Weight update in particle filters
For particle filtering weight update, often the transitional prior is used for the proposal density, in which case the weight update simplifies to just the likelyhood function. However, in one ...
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2answers
25 views
Camera image pixel structure origin
I am using machine vision for industry task with opencv. I have images from a camera monitoring the process. The detailed look at the small part of the image follows:
Enlarged:
In the detail, it ...
1
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0answers
26 views
drawing a line from where the tires meet the ground
I followed these steps to write a program in Matlab to detect the edge of the wheels where they meet the ground.
Step 1. read the image
Step 2. k-means segmentation
Step 3. Dynamic binarization
...
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0answers
12 views
Autocorrelation of vector of images
I have a set of images (think a ball getting bigger and smaller). I want to assess the periodicity in this string of images (each data point in my signal is an image). How can I go about doing this in ...
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2answers
32 views
Making sense of indices in 2D convolution operations
Referring to the answer here: https://www.quora.com/Why-are-convolutional-nets-called-so-when-they-are-actually-doing-correlations, the equation for a discrete 2D convolution is specified as:
$$C(x,y)...
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1answer
23 views
How do I detect the sharp edges in the following image?
I am looking to count the sharp pointy triangular things in the image. However I was unable to do so. One approach I did try was take a convex hull of the contour and then find convex defects but it ...
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0answers
22 views
What is a low pass kernel [closed]
Can someone tell me some common features of a low pass kernel? I have tried looking it up but i cannot find anything.
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0answers
23 views
Which noise reduction tecnique? [closed]
What is one of the most useful noise reduction techniques of filtering the Fourier space?
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1answer
16 views
Recommended approach for extracting specific edges from image?
I have several sets of images with a typical image being:
and from each image, I would like to extract the top and bottom curves of the object, shown in red here:
What are some possible tools I ...
1
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1answer
42 views
Outlined text extraction from image using OpenCV
I have some video frames I'd like to extract some text from (for making softsubs from hardsubbed video for learning). The text in question is mostly in Chinese script (some numbers and Latin letters) ...
1
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0answers
37 views
Robust custom watermark algorithms?
I'm doing research on image and audio watermarking, and so far I've read some literature in order to get basic introduction and good initial understanding of this topic. Right now I'm reading book "...
1
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2answers
29 views
The Gradient of Least Squares of 2D Image Convolution
Given the objective function:
$$ \frac{1}{2} {\left\| h \ast x - y \right\|}_{2}^{2} $$
Where $ h $ is the 2D convolution kernel and $ x $ is the 2D convolution image and $ y $ is a given 2D image.
...
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0answers
14 views
Optical flow Horn & Schunck smoothness error
I was reading about the Horn & Schunck method and they define the smoothness error as (Robot Control 1988 (SYROCO'88): Selected Papers from the 2nd IFAC Symposium p. 348):
$E_{sm} = \iint{\left(...
1
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1answer
24 views
What impact have different types of border-handling on high pass or low pass filtering?
When high or low pass filters are being applied to an (grayscale) image, the borders need to be handled separately. They could be filled with 0's or 255's (b/w), repeat the nearest pixel value, or ...
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0answers
4 views
Why can ARSS not recreate audio from a spectrogram without sounding muffled?
Why do ARSS and all audio to spectrogram then back to audio program's create audio files that sound muffled?
I know their is some physics and math with the short-time Fourier transform and etc. I ...
0
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0answers
15 views
Find specific feature within an image / Neural Networks
i am working in the field of image processsing and we have a certain problem which is difficult to solve by rules-defined algorithms.
Is it possible to teach a certain pattern into a neural network, ...
0
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1answer
23 views
Are there any efficient algorithm to detect circular shape of arbitrary size in an image?
I have images that are 1278 by 1024. They are pictures of a certain product that is rectangular in shape and are about 25mm by 20mm. As a part of a quality inspection process using computer vision, ...
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2answers
768 views
Career in signal processing
I am doing my MSc in electrical engineering, and there are not many courses in my university on signal processing. I want to develop my skills in signal processing such that I have a hold in one ...
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2answers
38 views
Definition of difference between compression and filtering
I'd like to explain the motivation.
It sounds like a neuroscience topic but I am after the strict Signal Processing POV.
(I don't come from a Signal Processing background).
Interested to learn ...
0
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0answers
25 views
urgent: MRI calculations question
I have a biomedical imaging exam tomorrow and I'm struggling quite a bit with this question below (from b-d). I was hoping someone could help answer these questions or at. I'll describe my approach to ...
0
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1answer
14 views
Similarity or Relation between Walsh Hadamard Transform and Slant Transform
Is there any relation between Walsh Hadamard Transform and Slant Transform? Or is there any common property or similarity?
0
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2answers
44 views
Image Brightness on 2D Fourier Transformation
What effect does the brightness have on the frequency spectrum of 2D Fourier Transformation?
Example. Suppose we have a gray image and calculate 2D Fourier Transformation. Then we increase the ...
0
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1answer
82 views
Amplitude demodulation of sinusidal signal in matlab
AM-demodulation task and I was asked to demodulate the signal in MATLAB and the result should contain three pictures.
plotting the $fft$ the (frequency spectrum)of the signal i was able to determine ...
0
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1answer
19 views
Linear Panorama Transform
I am trying to create a linear panorama (a series of images taken from the same plane but not the same location and not rotated) but was not sure which transform is appropriate for this task. I know ...
1
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1answer
30 views
How to interpret PSNR value?
Say, I have original image, noised and denoised. By PSNR value I want to find out how good does my denoising algorithm works.
For which pair of the images should I calculate it? I've tried it for ...
0
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1answer
25 views
MATLAB Image-Processing Toolbox: asking for a roadmap!
I plant trees in the north of BC for a living and have next to
none sp experience, please be gentle :^]
TLDR:
The problem is essentially this:
tracking and calculating the "height" of three ...
1
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4answers
72 views
Apply Principal Component Analysis for RGB Images
I've implemented a method to compute PCA on grayscale images.
I haven't seen PCA on RGB images yet, which left me wondering if it is possible to perform it.
With RGB images, is PCA done for each ...
0
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0answers
7 views
Response function for digital camera pixel
To help me with doing some signal processing on an image, I'd like to model how a digital camera works.
The camera has a bunch of pixels. What is the relationship between the value of that pixel in ...
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0answers
27 views
Recreating an image from random samples?
Assume that I have samples from an image, but the samples aren't on a grid, but instead there are multiple lowres versions of the original where the sampling locations are slightly jittered, so the ...
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0answers
32 views
Camera obstruction detection
I'd like to detect if camera view is obstructed (fully or partially) by some object (paper, hand, some device, etc).
Do you know any good methods for this task?
I've already experimented with:
RGB ...
0
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2answers
37 views
What do the 1D filters represent when using imfilter?
I am reading the source code of an algorithm that is used to process an image. While reading this source code (and others), I've found lines of code of the form
...
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0answers
23 views
How to create 3D signed distance function?
I am trying to segment a 3D shape using levelset. I want to track shape movement in consecutive frames.
Now I want to create a signed distance function matrix for ...
2
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0answers
31 views
How does the “additive operator splitting” exactly work?
I am reading about the non-linear (or non-homogenous) diffusion method (aka anistropic diffusion method). There are several ways of implementing this method. In all cases, we first need to discretise ...
0
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1answer
17 views
Why is the anisotropic diffusion equivalent to the heat equation when using a constant diffusion coefficient?
The anisotropic diffusion is defined as
$$\frac{\partial I}{\partial t} = \mathrm{div} \left( c(x,y,t) \nabla I \right)= \nabla c \cdot \nabla I + c(x,y,t) \Delta I$$
where $\operatorname{div}$ is ...
0
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0answers
48 views
How can I calculate homography from the room height and camera calibration matrix?
EDIT2: I've added an assumption that the camera calibration matrix is given. Other factors (rotation, camera pose) are still not given.
I want to measure actual lengths of floor edges (blue lines in ...
4
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1answer
156 views
Efficient implementation of 2-d circularly symmetric low-pass filter
How can a two-dimensional ideal circularly symmetric low-pass filter or its approximation be efficiently implemented on data sampled on a square grid? I'm referring to an ideal filter with a spatial ...
1
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2answers
58 views
What Is the Relation Between Deblurring and Deconvolution in Computer Vision and Image Processing?
The deblurring problem can be modelled as follows
$$
f = \phi u + \epsilon, \; \epsilon \sim N(0, \sigma)
$$
where $\phi$ is a filter (e.g. a low-pass filter) and $\epsilon$ is a Gaussian noise.
In ...
1
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1answer
28 views
is there a use for a changing kernel in image convolution
I understand the principle of image convolution. Maybe. I think it is this:
You use a small matrix with numbers in it,
then take a sample of an image with as many pixels as you have numbers in your ...
1
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1answer
32 views
Why entropy value can be used as measure of contrast of an image?
I was looking for value that can measure a contrast of an image. And I found a couple of answers like this one https://stackoverflow.com/questions/13397394/how-to-measure-contrast-in-opencv-visual-c/...
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0answers
54 views
What are the limitations of Watershed Segmentation Algorithm?
I am developing an Android application using Opencv to detect objects from images.
I used Canny edge detector to detect the edges and extract contours, and it's working good so far.
But I need to ...
0
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1answer
39 views
OpenCV warpPerspective implementation
I've implemented the least squares method to find the homomorphic image to fix the rotation and projection in an image.
Now I'm trying to implement the OpenCV warpPerspective method in order to "fix" ...
