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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Cross Correlation Matrix

In my group, we have developed an algorithm which shows abstract information from quantum mechanical systems as images. This way, given a quantum system, we obtain an associated image which has the ...
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1answer
115 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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1answer
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Image Filtering by Averaging Similar Areas of the Same Image - Patch Based Processing

I heard of filtering algorithms which, to filter an image specific area, find similar areas in the image and average them to reduce the noice of the original area. E.g. an edge of a house can be more ...
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1answer
112 views

How to transform an aerial image

This is the first time I'm diving a little deep into images and computer vision. I have an aerial image taken from a drone (I know the pitch, roll, yaw of the drone and the angle of the camera ...
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1answer
34 views

Producing images with subpixel shift in region of interest

Let's say for a zebra image, and at certain pixel location, I would like to makes it "vibrate/warp" to and fro in horizontal direction at a certain frequencies in a sequence of images of time ...
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4answers
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How to extract traffic signs from a photograph?

What image analysis techniques can I use to extract the traffic signs from an image such as the one below? Edit: After Anisotropic diffusion: The background that i don't want gets cleared a little ...
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2answers
474 views

Convolution of an Image with a Kernel That Is a Product of Two Functions

Suppose that $G(i,j)$ is a Gaussian decay function on the distance between points $i$ and $j$ of an image. In addition, $D(i,j)$ is the difference between the VALUES of the image at those points. Now,...
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1answer
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Ambiguous results of phase correlation in pattern recognition

We are using phase correlation to find pattern on image and what we get is 15% of results is spurious. Ours pattern has 32x32 pixels and image for research has 32x512 pixels. So we put Pattern to ...
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1answer
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Why do we use Difference RGB to grayscale function?

I found this function for RGB to Gray scale converter at this kind: RGB to grayscale This example converts an image with RGB channels into an image with a single grayscale channel. The ...
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Processing Multiple Images to Detect Moving Object in Low SNR Conditions

I am new to this forum and new to the use of Fast Fourier transforms although I can program in Python 3 a bit. I have an unusual question and am seeking some general advice on (a) whether what I am ...
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1answer
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Difference Between Correlation and Convolution in the Context of Image Processing

Could you please clearly explain what is the difference between correlation and convolution that is done by a filter on an image? I mean in terms of signal processing definition I know that ...
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2answers
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Performance of MATLAB's `conv2()` vs. `imfilter()`

A lot of people use imfilter to achieve a 2-D convolution between an image and a filter, but the majority of people use conv2 ...
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1answer
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Corner detection using Chris Harris & Mike Stephens [duplicate]

I am not able to understand the formula, What is $W$ (window) and intensity in the formula mean, I found this formula in opencv doc http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/...
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How do i calculate the accuracy of an algoruthm?

I'm doing research on an machine learning image processing algorithm (segmentation algorihtm)i.e. computer vision performs when an image takes as an input and objects in an image are segmented and ...
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1answer
117 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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3answers
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Why normalize the data set before applying Direct Linear Transform

Direct Linear Transform (DLT for short) is a method of homography estimation, it solves the overdetermined linear system via SVD $$Ah=b$$to find a solution $h$ under constraint $\|h\|=1$. Actually it ...
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1answer
219 views

How to detect the maximum resolvable spatial frequency of camera?

I am trying to calculate the minimum line pixel width that can be distinguished from noise as shown in the camera test chart in Figure 1 where the thinner lines on the left are getting more and more ...
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2answers
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How do you interpolate between points in an image (2D), e.g. using splines?

I can understand just fine how to use 1-dimensional interpolation on data points where one coordinate is a function of the other: y = f(x). However, when we have an ...
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1answer
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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 ...
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1answer
241 views

Getting different results when running my program at different times [closed]

I am working on Speckle Noise reduction in Ultrasound Images using MATLAB R2013. I have designed 10 basic filters and trying out hybrid combination using these filters. When I run my program I get ...
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5answers
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How to separate a low amplitude signal of same frequency but different phase

I have a signal consisting of two sine waves of same frequency but have different phase (and also a lot of HF noise). Their amplitudes differ by about $120\textrm{ dB}$. How to I go about separating ...
3
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1answer
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Generate the Matrix Form of 2D Convolution Kernel

We know that a convolution can be replaced by a multiplication with a Toeplitz / Circulant Matrix. Meaning, assume I have convolution kernel $ h $ and matrix $ I $ (Of size $ m \times m $ for example),...
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2answers
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What Is the Algorithm Behind Photoshop's “Black and White” Adjustment Layer?

Can someone explain the algorithm behind the "Black and White" adjustment layer in photoshop? I have to reproduce it using C++ for an application that emphasizes non-red/magenta(ish) pixels from an ...
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1answer
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How do I evaluate the performance of a segmentation algorithm?

I'm currently on a project of liver tumor segmentation. I segmented the liver using region growing, and I have to assess how accurate the result is. I recently learnt that there are certain metrics ...
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1answer
36 views

Identifying the boundary points of a shape based on the centroid

I have a set of binary 2D images with objects in white and their boundaries in black (attached example). I also have a list of centroids (x,y coordinate pairs) identifying all objects. For each ...
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1answer
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removing vertical lines in grayscale images by thickness

Suppose we have a grayscale image that contains vertical lines. Now suppose that not all vertical lines are the same, some of them have different thickness. Question is, is there a way, in MATLAB or ...
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328 views

Spatial wavelength

I was reading a paper on motion magnification, Eulerian Video Magnification for Revealing Subtle Changes in the World by MIT CSAIL researchers, where the equation (14) of the paper uses spatial ...
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2answers
508 views

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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0answers
156 views

Residual error when setting measurement matrix in compresssive sensing

I have an issue when implementing compressive sensing to recover sparse vector. Assume I have sparse vector $x$ of length, for example, $(256,1)$. $x = [x_1,x_2,.....x_{256}]$. This vector is ...
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1answer
31 views

How to prepare different input size in CNN

I'm doing a research about personality identification based on their signature using CNN method, however the learning feature for the personality traits have a different input size. I understand that ...
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1answer
37 views

These two images are very similar. Why doesn't SSIM reflect that?

Here are two aligned images (greyscale, but same applies to RGB) that I want to compare using SSIM: Clearly, these are very similar images. It seems that the first image is more blur rr However, the ...
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1answer
446 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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1answer
308 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
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Shifting Image with MATLAB Code [closed]

img = rgb2gray(imread('lena.bmp')); imgFirstHalf = img(:,1:2:end); imgSecondHalf= img(:,2:2:end); implay(cat(3,imgFirstHalf,imgSecondHalf)) Now the question I ...
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1answer
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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?
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1answer
276 views

Analytical Expression for Convolution of Two 2D DFTs

I am trying to do an image analysis problem on some images, and I want to calculate some things in the frequency domain which are giving me problems. Say I have an (discrete) image $I(x,y)$ of size $...
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0answers
83 views

Image processing for camera health monitoring

I have a set of cameras. I would like to monitor the output of the cameras to make sure they are operating well. So far my ideas: standard deviation and the mean of the picture - to find out if the ...
2
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1answer
97 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 ...
0
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1answer
34 views

Low samples numbers machine vision training for object detection

I'm trying to set-up a machine vision application in which I have to detect the position of a printing nozzle (in the red sqaure in the image) in a field of view in order to prcisely position a ganty ...
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4answers
2k views

Apply Principal Component Analysis (PCA) 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 ...
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0answers
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Unexpected Results in Rank Transform Based Disparity Estimation

I am applying a normal rank transform of size 7 x 7 to the right/left shifted images in order to obtain their disparity map using a typical block matching algorithm in MATLAB. My code to obtain to the ...
3
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2answers
102 views

Convolution v.s. Cross Correlation in Digital Image Processing

I understand that from mathematical point of view, only difference between Convolution and Cross Correlation is that Convolution is commutative, while Cross Correlation is not. In many articles ...
4
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1answer
101 views

On the Measurement Matrix Used for Compressing Sensing

Assume we have a matrix $x$ of size $(8,8)$ where each column is considered to be sparse with degree of sparsity equals to $4$. it means that every column can have $4$ zeros and $4$ non-zeros values ...
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3answers
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What Do Skewness and Kurtosis Represent?

I understand that the question could mean a lot of things but I am thinking specifically to image processing. For example, I know that the mean can be a basic texture feature that represents the ...
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1answer
750 views

What Do We Expect Likelihood Function to Be Used For?

In my understanding, I let make a example. For example, you can see in the following picture. Consequently, We want to find ^sigma. and We have already known the observation data(which is random ...
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1answer
66 views

Determining Parameters of S Function for Image Global Contrast Enhancement

I know that S-function (membership function from fuzzy set theory) is a commonly used function for image enhancement. I am reading a paper titled - A Novel Fuzzy Image Enhancement Using S-Shaped ...
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0answers
21 views

remove outlier spectra

I have a set of spectra (hyperspectral imaging) per class (~10000) and want to remove those spectra which behave different then the mean of the spectra. I want to remove the entire spectra (not ...
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5answers
17k views

Good Language for Implementing Computer Vision System / Algorithm / Application?

I am trying to implement a content based image retrieval system but before I do so I would like to get an overview of some programming languages suitable for this task (having good libs and such). ...
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1answer
1k views

How Do I Plot Color Distribution of HSV Image in MATLAB

I have a dataset of images representing human skin. How do I plot the skin color distribution in HSV color space and YCBCR color space. However, I'd like ignore the "value" or "brightness" in both ...
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2answers
54 views

Image Processing in MATLAB

We try to multiplication operation of a black & white image with RGB image in same image but their class is not same: BW -> logical, RGB -> UINT8. How can I convert from Logical to UNIT*? Or, can ...

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