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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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120 views

Convolution Offset and Factor in Frequency Domain

See this link. The following Convolution in Spatial domain code is written in C#. ...
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Chapter 4, section 4.2.1. in Szelisky computer vision, is there a mistake?

I've already asked a similar question in mathematics exchange without getting an answer, I read a bit more and I think the question might be more suitable for the signal processing exchange. ...
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Output of a bank of gabor filters, derive ellipses like regions

I'm trying to implement an algorithm that show how to detect wrinkles in clothes, without going to much into details this is the step that is confusing me. Assuming we have an image $I$ and a set of ...
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1answer
52 views

How Does Mean Centering Affect the Result of Using SVD to Compress Images?

I have been learning about using the Singular Value Decomposition to find low rank approximations to matrices. I had an image which I converted to a matrix. I regarded each row of the matrix as a '...
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Using feature detection as weight function in non linear filtering energy function

In image processing \ computer vision It is known that some filtering operations can be formalized as $$ E(u)=\int_{\Omega} \lVert u - f \rVert^2 + \lambda \lVert \nabla u\rVert^2 d\Omega $$ ...
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1answer
52 views

What Is a Weighted Local Histogram?

I'm reading through a couple of academic papers, and this terms often comes up "local weighted histogram". An example of quote is the following: First, cumulative histograms are built for every ...
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1answer
95 views

Count Matches to a Kernel

So, I have this problem where I want to apply a kernel to an image and count the number of matches that happened. So for example, if I have the kernel: $$\begin{bmatrix} 1 & 2 & 1\\ 1 & ...
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1answer
241 views

Laplacian of Gaussian Approximation and Gaussian Blur as the Solution of Heat Equation

While I was reading SIFT paper(Lowe, 2004), I came across the method that he apply "heat diffusion equation" to Gaussian function to derive that $$ \frac{∂G}{∂σ} = σ∇^2G $$ I searched Wikipedia and ...
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78 views

detecting specific words in images?OCR?

i'm not sure if this question belongs here or in stackoverflow but i feel like it belongs here as it is more about the approach than the code itself. i'm trying to write a program that searches in a ...
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1answer
66 views

Transforming Non-Uniformly Sampled Image onto Rectangular Grid

I have an image and associated latitude and longitude matrices. So I know the latitude and longitude of every pixel. However, due to the camera orientation, the image is skewed and thus the latitude ...
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1answer
479 views

Fastest Available Algorithm to Blur an Image (Low Pass Filter)

Iam working with a camera that produces ugly artifacts: by using ANY blur filter on the camera's output the visual quality improves drastically: The above image was created using OpenCV's cv::...
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2answers
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How can I remove flickering background in a video?

I have a black and white video taken with a high speed camera and I notice a background flickering coming from my LED light. The images alternate from dim to bright and it makes the videos quite ...
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2answers
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What is the relation between kernel functions, kernels used in convolution and null spaces of a matrix?

I have recently started learning about machine learning and have come across kernels and null spaces. I understand that null space is the set of all vectors that satisfy the equation A.v = 0 (Where A ...
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43 views

How to produce the Semantic Segmentation Dataset?

I am preparing my own synthetic data-set, to pre-train my deep learning model. I have produced images and there corresponding masks using some python scripts, but I am not able to find the way of ...
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1answer
210 views

The Differences between Super Resolution and Denoising and Deblurring

In the field of computer vision/image processing, what are the differences between super-resolution and de-noising/de-blurring? Thanks.
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1answer
132 views

Correlation peformed by convolution

Background: The question here is related to images in particular and not signal/waveforms. I have been reading a lot of answers about the difference between convolution and correlation but I am stuck ...
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1answer
52 views

How to measure the distance between two circle-like-lines over 360 degree

I am looking for a slim and with that quickly programmable image processing strategy to measure the distance between two circles over 360°. It is important to notice that the circles are not perfect, ...
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1answer
186 views

Binarization, and then thinning/skeletonization

I have pictures of networks, like the one below, and my goal is to obtain the network's skeleton from processing those images. My approach lies in two steps, first I convert grayscale image to binary ...
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1answer
37 views

Is the Bilateral Filter a Solution of Some Variational Method?

I've been watching these video lectures about variational methods in computer vision. In one of such video lectures a it is explained for example that the Gaussian filtering is a solution of the ...
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1answer
48 views

The Gradient Operator of a Vectorized Image in Matrix Form

I have this optimization problem: $$ \arg \min_{ X \left( i, j \right) } \sum_{i, j} \left\| X \left( i, j \right) - 255 \right\|_{2}^{2} + \lambda \sum_{i, j} \left\| \nabla X \left( i, j \right) - \...
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1answer
111 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 ...
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1answer
76 views

How to Approximate the File Size Ratio of Two JPEG-LS Compressed Images? [closed]

For instance, a high-resolution image (25MP) and a low-resolution image (4MP) of the same scene. When compressing them both with ...
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2answers
39 views

How Can JPEG Be Used to Realize a Transfer Application with a Fixed Bit Rate? [closed]

For simplicity, assume a fixed bandwidth (5MB/s) and that each second an image with 12MP is generated. The quality of the image ...
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1answer
28 views

Most reliably and rapidly readable 2D barcode?

QR Codes are far and away the most popular 2D barcodes for mobile applications these days. However, there are several other widely-used 2D barcode symbologies as well, including Aztec (used in the ...
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1answer
688 views

Scale invariant template matching

For my application I am looking for a free, fast and scale-invariant template matching algorithm. The templates can only be scaled within the scene (no skew or rotation) and the scale is unknown. ...
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1answer
81 views

Circle detection with incomplete edges

I want to detect circles in the image below but this approach, of using cv2.approxPolyDP on contours and counting the sides of the polygon, doesn't work here since some of the circle is missing. Is ...
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1answer
92 views

What Are Different Approaches to Realize a Gaussian Blur (Smoothing) Step on an Image? [closed]

Could some review some methods to apply Gaussian Filter (Blur) on an image besides the direct one using Truncated FIR (classic convolution with Truncated Kernel) approximation?
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Image brightness and contrast adjustment on stereo image pairs

I have a pair of stereo images captured with two different cameras. They differ in brightness and contrast as they were not captured with global shutter cameras. I need to apply semi global matching ...
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2answers
415 views

What is a filter bank?

Suppose, I have 3 kernels: $$ \left[ \begin{array}{cc} a&b&c\\ d&e&f\\ g&h&i \end{array} \right] $$ $$ \left[ \begin{array}{cc} p&q&r\\ s&t&u\\ v&...
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2answers
236 views

Gaussian pyramid: why needs the image to be downsampled

In the context of a gaussian pyramid, why is the image downsampled separately although the numbers of pixels are decreased through smoothing already? In my understanding, the number of pixels will ...
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1answer
53 views

opencv otsu binarization not working

I tried to apply opencv OTSU binarization on the following image, but it generate a black image. Here is the following python code: ...
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1answer
544 views

Is there a penis detection demo similar to face detection?

Tutorial for face detection: Is there a script / tutorial / demo for penis detection? These guys ran into some issues: Fairly serious question, future of internet memes is at stake. Breast / ...
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2answers
61 views

improving pre-processing (noise removal) orange seven segment display for OCR reading

About this project: Older images have the date they where taken placed on the image, in the bottom left hand corner. The goal is to extract this date and put it in the EXIF data of the scanned photo. ...
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1answer
183 views

Intuitive Meaning of Regularization in Imaging Inverse Problems

Hello Every one I have been trying to understand the intuitive meaning of using a regularizer in images. Specifically what does the Total Variation regularizer do in images and how is it able to ...
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2answers
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Is SSIM a measure of mutual information?

As i have seen contradictory information online: is the quality measure SSIM between two images (one base-line, one distorted) directly correlated to the mutual information between the two. One one ...
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2answers
81 views

Are there any quick way to tell if a kernel is a high-pass filter?

Im new in this image processing field so please be gentle with terminology, i have a kernel of 3x3 and i want some way in order to test if its a high pass filter or not Thanks in advance
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0answers
121 views

How to flatten this OCT image with respect to the marked line

I am working on a medical image processing project where I have to use retinal OCT images. I am using the dataset available here. This dataset has a lot of images and I want to flatten all of them. I ...
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91 views

Feature Extracting from an image from JAFFE database using gabor filter

I am trying to implement a feature extractor using gabor filter in MATLAB. I have taken images from the JAFFE Database. Here is my code: ...
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1answer
57 views

How to make series circle shift invariant

I have a series of numbers. They may be integer, floating, or ...
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1answer
168 views

Subtracting DC Offset a Complex Signal?

If I take the magnitude of a complex signal, and then subtract the mean amplitude, I remove DC offset but lose the real and imaginary components. How can I properly subtract the DC offset of a complex ...
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15 views

Square grids in single-pixel cameras

I have read a few research papers where the authors used Hadamard matrices as masks for image capture. In almost all of them the arrangement of the mask is square, e.g., some use a Hadamard $4096$ to ...
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1answer
86 views

Wiener deconvolution in cpp giving back the same image

I was trying to deblur a noisy image using wiener deconvolution. I found this code which added noise to an image and removed it as well. Modifying this code only i tried to implement the exact formula ...
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1answer
52 views

How Can PCA Be Used in Image Analysis [closed]

I am still a not how PCA can be used in image analysis and where is it is mostly used. For example how can PCA be used in order to differentiate between different faces? Can you please mention other ...
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2answers
538 views

How to Classify a Kernel as Low Pass Filter (LPF) or High Pass Filter (HPF)? How to Transform an LPF Kernel into HPF Kernel?

The filter impulse response is [1/9 1/9 1/9;1/9 1/9 1/9;1/9 1/9 1/9]. how do i determine whether it is an Low pass filter or a high pass filter. If this is a low pass filter how do i convert it to a ...
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2answers
62 views

What are some current algorithm(s) for finding if two images are copies of each other?

Could anyone enlighten me on what are the current best ways to detect if two images are the same (i.e. a copy or edited copy of each other)? What feature detection method do they use (SIFT, DWT, pixel ...
2
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1answer
112 views

Gaussian Equivalent of Convolving an Image 50 Times with a Box Filter

I have a image that I'm convolving 50 times with a box filter, and I like to replace this with a single gaussian filter. Because both box filter and gaussian filter are separable I can just study the ...
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1answer
41 views

How does reconstruction function relate to watershed segmentation?

I'm trying to understand how watershed work by reading The Morphological Approach to Segmentation: The Watershed Transformation S. Beucher and F. Meyer This document mentions the reconstruction ...
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1answer
967 views

Use of the Sobel Filter for Image Gradient [MATLAB]

I am using the Sobel filter for an RGB image. I have found two different ways to do that and the results look a little different. What is the difference between these two methods? Method 1 ...
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1answer
1k views

Convolution and cross-correlation on 2D image (Example)

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 ...
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Fast Calculation of Legendre moments in images using kernel-separability

I am implementing zero order approximation method to calculate Legendre moment of an image. One simple way to calculate moments is directly using loops and calculate the double summation as given in ...