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.

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22 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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2answers
99 views

Estimating an Image Filter from Examples

I am sure this question must be fairly easy and could have been answered on this site but perhaps I am not finding the right keywords to search for it. I would like to know what are the common ...
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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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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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Removing noisy lines from image - opencv - python

I want to process different type of image to extract actual text from noisy image .I am using open cv to do this job it is working fine but the problem is I need to set different lower threshold to ...
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can I combine 2 raster with wavelet transform in R? [closed]

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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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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1answer
517 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 ...
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55 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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2answers
34 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 ...
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31 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
67 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
2k views

Otsu Thresholding : Why 'minimum within class variance' gives the optimum threshold?

I was trying to understand the Otsu thresholding algorithm in image processing. For that purpose I found a useful link. I got the algorithm flow, but a fundamental doubt arises. Why 'minimum within ...
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1answer
622 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) ...
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1answer
443 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" ...
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3answers
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Difference between SNR and PSNR

I understood that SNR is the ratio of signal power to the noise power. In terms of images, how the original image is affected by the added noise. In PSNR, we take the square of the peak value in the ...
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1answer
233 views

Poisson Noise Removal from an Image

What type of filters can be used to remove Poisson noise in an image? I tried applying Gaussian filter to few points in the spectrum.
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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 "...
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Image Processing - What Is a Gradient Domain?

What is the gradient domain? Does it relate to the Laplace Pyramids? I found only articles assuming you know what it is and not define it, can someone please define what is it and what it is used for?...
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2answers
404 views

2D Image Convolution: Spatial Domain vs. Frequency Domain Convolution in the Computational Complexity Sense

I want to convolve 2 images I1 and I2. Let's assume they have the same size. I know 2 methods: 1) Use direct definition of 2D convolution 2) i. Computer FFT of I1 (call it I1_FFT) and FFT of I2 (call ...
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1answer
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Image Gradient - Flipping Effect of the Convolution Matrix (Kernel) for Edge Detection

Prewitt operator is a common operator to compute image gradient in edge detection, and I knew that to apply this Prewitt operator to an image is just to convolve them together, say, the image is ...
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What Techniques Are Used for Signal / Image Denoising (Example Image Provided)?

I have an image that looks like this (it might appear low res in a browser because it is 16 MB). This image was taken with a scanning electron microscope, but because the equipment is outdated there ...
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1answer
197 views

2D Digital Signal Processing - Applying High Pass on and Image

I have been doing my research on 2D digital signal processing. What I am doing is about noise removal of digital image: Type of noise that I want to remove from an images is like the Gaussian noise ...
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1answer
805 views

Removing Noise from Dental Radiography

I'm working on a project of applying Active Shape Model to locate tooth in dental radiograph. For those familiar with the technique, I'm currently trying to sample along normal vectors for each ...
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5answers
23k views

Noise Removal from an Image Using OpenCV (Comparison to Neat Image)

I tried removing noise from the image shown below using Median Blur in OpenCV. But i'm not able to remove the colour noise completely as it is done in Neat Image. Any suggestions.? 1. Original Input ...
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1answer
865 views

Remove Checkered Noise (Pattern) from an Image

I'm trying to remove what looks like a checkered noise pattern that has been added to an image. Comparing the 2D FFTs The one on the left is the original, while the middle one is the corrupted one. ...
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2answers
255 views

Filter for Reducing Background Noise in Image

I have images where there is a lot of "black" background (few shades of black). (In many images at least half the pixels are background). I need to get interest points from the image, but because the ...
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1answer
609 views

Removal the DC Component of Gabor Filters

I recently was studying gabor filters and came to know that they have a shortcoming that they do have a minimum but some reasonable dc component. now my question is why is it necessary to remove the ...
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3answers
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How to Remove Gaussian Noise from an Image without Destroying the Edges?

What is the best filter for removing Gaussian noise without destroying the edges? I am using the standard Lena images with additive Gaussian noise and I want to denoise before applying anisotropic ...
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2answers
54 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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1answer
1k views

Implement the 3D Structure Tensor in C/C++?

I am trying to figure out the details on how to implement the 3D structure tensor in C/C++ in an easy but efficient way and need some advice! For a discrete function $ I(x_i,y_j,z_k)$ the 3D ...
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1answer
156 views

How to Calculate the Hann Low Pass Filter / Kernel for Image Processing

I'm currently studying for an exam in image processing and stumbled upon a exercise which i could not answer and my professor will not be available before the exam anymore. The exercise goes as ...
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2answers
127 views

Finding the Width of a Point Spread Function (PSF)

I have a binary image that has been convolved with the following PSF: $$\mathrm{PSF}(x,y)=\cosh^{-2}\left(\frac{\sqrt{x^2+y^2}}{w}\right)$$ where $w$ is unknown. The image binary image generally ...
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1answer
780 views

Formula for 2D Image Filter for Scratch Detection

Consider Multidirectional Scratch Detection and Restoration in Digitized Old Images Research Paper. In section 4.1 (Preprocessing), they gave us a formula of the kernel, $$ H(u, v) = \frac{1}{1+0....
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1answer
64 views

Histogram of Gradient

I was calculating which would be faster in computation, Inverse Fast Fourier Transform or Histogram Of Gradient but I am unable to calculate its running time. What would be the running time of ...
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1answer
2k views

Scanning from Book - Gradient Removal

This sample image: is warped on the left side. I don't want to dewarp, but just to remove shadow gradient (caused by book's spine). I guess gradient can be calculated from upper part of the image ...
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1answer
176 views

Convolution in Image Processing

Does anyone know how to write arg min code in matlab with explanation? I am referring to a paper for my research. I am not sure whether I can paste the paper link here. At first, I try to do feature ...
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1answer
146 views

Wiener Filters - Obtaining /Estimating Image and Noise Spectrum

We all know the famous Wiener Filter, $$G(\omega_1 , \omega_2)=\dfrac{H^*(\omega_1 , \omega_2)}{|H(\omega_1 , \omega_2)|^2 + \dfrac{N(\omega_1 , \omega_2)}{S(\omega_1 , \omega_2)}}$$ How to we use ...
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2answers
63 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 ...
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1answer
1k views

Convolution Based Image Interpolation

From a book, I learned that image interpolation (or upsampling) can be written as a convolution like this: $$g(i,j) = \sum_{(x,y)}f(x,y)h(i-rx,j-ry)$$ while $r$ is the upsampling rate. But I have a ...
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1answer
2k views

Convolution in Image Processing?

I got the concept of Convolution in signal processing from a video lecture that it is method to get the area overlapped between two signals when one signal is flipped over and traversed over another ...
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1answer
307 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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1answer
595 views

How to Do Convolution a 2D Signal (Image) and Result of Convolution of Two 1D Filters?

Assume a 2-D signal (i.e., some image). Load image and assume it to be signal x. Next assume that instead of having a 2-D filter you have two one D filters $$f_1[n] =\begin{bmatrix}0.25 && 0....
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1answer
134 views

Detection Algorithm in 2D Images

Suppose there is a two-deimensional image which consists of pixels. In every pixel, there are 0 to n apples with different colors, which can be digitalized(e.g.[0,10000]). So we can plot a histogram ...
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2answers
110 views

Generate 3D image from Multiple 2D Images

If we're to capture an image of a body using four (4) WebCam with a 16 megapixel (1 in the front, 1 in the back and 2 sides(left and right)). Is it possible to make a 3D out of it using image ...
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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 ...
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1answer
215 views

Morphological Gradient Versus Linear Gradient in Image Processing

To obtain the gradient from an image, one can use a linear filter that for example is derrived from the derrivative of a gaussian. Then convolving the image with this linear filter gives you the ...
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2answers
12k views

How to Compute Image Gradients?

How to compute Image gradients? In X Direction - Kernel : -1 0 1 In Y Direction - Kernel : -1 0 1 Let's assume my input image is: unsigned char* imgImage; ...
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1answer
427 views

2D Convolution in MATLAB Causes Artifacts (Boundary Issues)

I`m trying to do a 2D fast convolution in Matlab of large matrices. If I use FFT version based on convolution theorem ( https://en.wikipedia.org/wiki/Convolution_theorem ), there are some artefacts in ...
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1answer
2k views

Convolution and Cross Correlation on 2D Image

I have read that convolution and cross-correlation are the same thing, but convolution flips 180 degrees (images), or time reverses (sequences) the kernel, before performing the elementwise ...