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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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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 ...
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22 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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39 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 ...
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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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How to implement Just Noticeable Difference(JND) of an Image [on hold]

I want to implement the algorithm of 'Just Noticeable Difference'(JND) of an Image with python-opencv or c++.
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After advice about detecting focus quality of objects in a photo detected using YoloV3

I've spent the last couple of days playing with YoloV3, and have had very good results. My use case is sports photography, and the object detection for people/bikes etc is very very good, I'm very ...
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18 views

Understanding SURF point-of-interest localization

I've recently read Herbert Bay's paper of SURF. From which I understand: SURF calculates a table from each image pixel's Hessian matrix's determinant, instead of SIFT's Difference-of-Gaussian table. ...
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What are the meanings of Fx, Fy, Sx and Sy in Image Processing?

I am currently reading a book titled "Learning OpenCV 3 Computer Vision in C++ with the OpenCV Library", and I come across these two equations: ...
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Once spines recognized, how do I find each individual book?

I want to make a system like the Book Spine Recognition on Youtube. So I read research paper and I built this system. According this paper, I use Hough transform, then I recognize book boundary ...
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55 views

2-d circularly symmetric low-pass filter

For a square pixel grid, the ideal 2-d low-pass filter with a horizontal and a vertical cut-off angular frequency $\omega_c$ in radians has an impulse response (kernel) $h_{\small\square}(x, y)$ that ...
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9 views

How to warp and enlarge the center of an image?

I am trying to smoothly enlarge the center part of an image. The Skimage code that I use need an inverse map that specifies location of input pixels that will occur at the output pixel location. If I ...
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OpenCV: How does bitwise_not work?

I am experimenting with the OpenCV-library in python. Let's say I read in an image such as: ...
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How to Combine / Cascade two `3 x 3` Filters into One `5 x 5` Filter

If you have a uniform 3x3 box filter T which is: 1 1 1 1 1 1 1 1 1 And an 3x3 laplacian filter W which is: 1 -2 1 -2 4 -2 1 -2 1 Can these 2 filters be combined into one 5x5 filter, the ...
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Implementing Edge Preserving Diffusion (Anisotropic Diffusion)

I am trying to implement edge preserving diffusion. Recall the general diffusion equation to be: $$\DeclareMathOperator{\Div}{div}\delta_t u = \Div(g \nabla u)$$ Where $g$ is the speed of the ...
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170 views

Autodetecion of 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, ...
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Block Diagram of Digital Image Processing [closed]

I was preparing a short report. I got confuse in making the block diagram of DIP. How does the Digital image processing block diagram look like?
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How to use a found homography matrix H to transform an image? (MATLAB)

Following is my procedure to find homography matrix(H): 1)Pick 6 pairs of correspondence on two images(images of the same object but in different angles) 2)normalise (normalise2dpts()) the points ...
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How to uniquely identify the numbers from a given map (image)

I have to uniquely identify the numbers from a given map, which represents the the various regions according to their elevation using numbers.
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Efficient way to compute how much light is present in a scene (for camera focusing)

I'm developing somewhat of a camera app and need a way to compute how much light is present in a specific scene to know how to adjust the exposure and iso level so that the focused point will detailed ...
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1answer
18 views

Why does the Y component in YCbCr represent luma/intensity?

As far as I know, the RGB to YCbCr conversion is just a linear transformation, yet the Y channel successfully captures the intensity value of each pixel. How? In other words, where do the following ...
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1answer
14 views

Estimate gap between two adjacent images

I have two images of a panoramic view but there is a small gap (<24 pixels) in the horizontal dimension between them. I would like to do interpolation/inpainting to fill the gap, but the exact size ...
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29 views

How do 2D DCT basis functions interact to produce 8x8 JPEG tiles?

This section is a bit of an intro. If you want to skip directly to where the problem is explicitly outlined, skip to the bottom of this post. Please note that I'm not hip with mathematical lingo, so ...
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1answer
41 views

What is the result of fourier transform of an image

I am new to computer vision and Fourier transform concept. I have examined some codes. In those codes, an image is performed Fast Fourier transform by using the function ...
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How to harvest the highest amount of information from an image?

I wrote a script that detects objects, crops the part of the image where an object is located and tries to increase the quality of cropped image. The object detection runs tensorflow. To increase ...
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2answers
60 views

Help understanding MATLAB code [on hold]

I need some help understaing some MATLAB code: The function takes an input of 8x8 matrix and outputs a 63x1 array, I understand that it goes through the matrix in a specific zigzag way (Picture ...
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Images as Markov chains

I have seen literature on representing black and white images as probability distributions and then computing "distances" between them, for example, in optimal transport. I was wondering if there is ...
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Requirement of time step in convolution output?

I am studying time domain analysis from book signals and systems labotary with matlab by alex palamides when i was studying convolution command topic on page 187, author discussed use of ...
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Image processing problems that make use of the theory of hybrid dynamic systems

This semester I am taking a course called "hybrid dynamical systems". So far we have seen how to model these systems, the properties of reachability and determinism. We have also seen the properties ...
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Concept of scales in Gabor filter

I've been reading about Gabor filters, and there is a concept of scale. While I understand that Gabor features help in analyzing both the frequency and orientations of an image, what is the idea of ...
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1answer
32 views

confused in difference between calculations of convolution and multiplication?

How are two signals multiplied? And how is it different from convolving two signals?? I have read the above question on dsp stack exchange and i also tried it in my matlab , code is as follow: ...
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Multi-light Image Collections fusion - not defined parameter

Description I am working on implementation of fusion method proposed by Fattal, R.; Agrawala, M. and Rusinkiewicz, S. in paper called Multiscale Shape and Detail Enhancement from Multi-light Image ...
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1answer
24 views

Isotropic and Anisotropic in the Total Variation Framework

The isotropic TV is defined as the estimation of 2-norm of gradients $\sqrt{(y_{i+1,j}-y_{i,j})^2+(y_{i,j+1}-y_{i,j})^2}$, while the anisotropic TV is defined as the estimation of 1-norm of gradients $...
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Satellite imagery color normalization

Satellite images available from public sources (Google Maps, Bing, ArcGis, etc) have a common "flaw" with color balance abruptly changing in places where two different images were stitched (perhaps ...
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Sampling Theorem for images

A medical Image has a size of 8x8 inches. The sampling resolution is 5 cycles/mm. How many pixels are required? Will an image of size 256x256 be enough? I know sampling in 1D signal but cannot get ...
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Why am I not getting the intended coefficients in this 2D Fourier demonstration?

I am trying to demonstrate how the 2D Fourier decomposition of an image works with Matlab and a very, very simple example. I create a 4 x 4 pixel image with cosine basis vectors as such: ...
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1answer
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How to Remove the Patch Artifacts of Neural Network Denoising Process?

I have written a python script which uses the Noise2Noise: Learning Image Restoration without Clean Data implementation of the Auto Encoder which is useful to remove noise from images. In the original ...
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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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Automatically crop out certain region around red objects

I have the image seen below and I would like be able to automatically crop out everything around each red section - not enough to overlap but enough that you can see how connected to the green parts ...
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2answers
57 views

Circular Convolution Matrix of $ {H}^{H} {H} $

We all know that Discrete Fourier Transform (DFT) corresponds to circular (not linear) convolution. That is to say, if $x(n),h(n)$ and $y(n)$ is the original signal, the filter and output signal in ...
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25 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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How to separate spliced(photoshopped) part from the rest of the spliced image?

I'm working on a project to detect spliced images and want 128x128 patches at the boundaries of the forged regions. I have the authentic background image and the spliced(photoshopped) one. If I ...
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Hisotgram equalisation error, help with my code

Iam working on implenting a histogram equalisation of an image without using inbuilt functions specifcally imhist and histeq, I have, for the most part understood what do during a histogram ...
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22 views

Elimination of image blurring using noise model restoration techniques

How can the blurring be eliminated from image using the noise model restoration process techniques? To my knowledge the answer must be filter.If yes,then which filter is used?
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1answer
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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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How do I denoise a microscope image?

I'm working in a computer vision project, where the goal is to detect some specific parasites, but now that I have the images, I noticed that they have a watermark that specifies the microscope ...
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2answers
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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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2answers
22 views

Extracting image metadata programatically

I hope this is the right location to post this, as my question isn't really stack-overflow material but involves images. I have hundreds of SEM-Images like this: and need to track changes in certain ...
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2answers
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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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Fresnel transform over image

You can recommend the literature or tell you what the Fresnel Transform does to the image. I realized that this describes the passage of a light wave through an optical element, but I need to ...
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2answers
80 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 ...