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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Image from Inverse FFT operation is sparse

I'm trying to train a deep nerual network that takes in input, an signal in the frequency domain, and attempts to learn a mapping to another signal in the frequency domain. Basically, the input to ...
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26 views

Text detection and recognition from Image

Let say you are given this image and want to detect and recognize the digits printed on the fuses. for all CV-operations i used OpenCV 3.4.4 and Python I did already these things: Detection: 1) ...
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34 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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25 views

What is a `patch expert'?

In many facial tracking algorithms based on constrained local models (CLM), such as this one and also this one, the first step of the algorithm is to learn a 'patch expert' which learns if a proposed ...
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19 views

Seperating two (image) signals in Fourier Space / Denoising

i have a problem here which is not so easy to solve. I have a measurement system which provides me two signals: -The "contrast" channel" - this is the main channel on the object -A second channel ...
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21 views

Retro Tiled Image Palettization Algorithm?

In most cases today, image palettization consists of reducing the overall number of colors in an image to some fixed number globally. This is typically solved as a straightforward but computationally ...
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22 views

Finding Local mean value of pixels of window

I want to solve the equation (2) in the attached picture which tells the local mean value. But i don't have any idea about how to evaluate this equation using matlab code. could only guess w indicates ...
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50 views

How to calculate the variance of noise when an image is downsampled?

I have a noisy image for which I know the noise variance. (Basically I created noisy image by adding noise). Now, I'm downsampling this noisy image. How does the noise variance change? Is it possible ...
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16 views

fitting lines based on image content with python

I trained an algorithm for road semantic segmentation that gives an output like this: I want to retrieve the coordinates of the vanishing point (the top of the triangle) and to fit two lines ...
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20 views

Switching camera angle based on several images

Given a number (3 or 4) of different images of a given subject from different angles, how do I interpolate to an angle that isn't available on any of the photos? What is this technique called and is ...
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23 views

problem in selecting correct algorithm for project (RCNN)

I am doing a deep learning project in which i have to identify different models of cars. i am a bit confused for the following reason: first is what algorithm should I use. I have studied that RCNNs ...
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40 views

Calculating the Mean Square Error (MSE) in Wavelet Denoising

I´m currently reading the paper (to be more precise: it´s a chapter from the book "Shearlets, Multiscale Analysis of Multivariate Data" by Kutyniok and Labate) "Image Processing Using Shearlets" by G....
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25 views

Is there a way to find a picture inside another picture, using only 2D Fourier Transforms of both images?

Can Fourier Transforms of both images tell anything about "likeliness" of two pictures? If yes, how precise? Can it still work if only several pixels are different or can it tell they are same if one ...
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102 views

Scratch Detection On Noisy Textured Surface

I wish to extract long thin scratches from the noisy background image.I have tried several ways such as stacking smoothed image with input image to remove some of the noisy background patch before ...
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113 views

retrieving complete 2d autocorrelation function from 2d power spectral density function (numpy.fft.ifft2)

My question is at the boundary between signal processing and python. I have a 2d power spectral density function (PSDF) constructed on Nx/2 + 1 and ...
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16 views

Amount of pixel eroded

Is there a definite relation between the kernel size and shape of a morphology change and the amount of pixels added or removed? I have a case where I have a segmented image, and I need to remove x ...
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16 views

Filter imaging based on the spectrum image

On the left I have the noised spectrum image can we choose which filter to work based on it? For example in the 3rd row it seems that all the energy is concentrated in the middle so we need to "...
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74 views

Detection of Video Quality Using Python

I am getting started with image/video processing. As a start I have a dataset for which the goal is to detect the quality as the video progresses. Based on my readings I think any video under test ...
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40 views

Polyphase FIR image downscaling

I recently started designing a Polyphase FIR filter in with a lanczos kernel interpolator to resample an image in Python. The goal is to downscale the image using these methods. However, I think I don'...
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9 views

Corresponding filter in the frequency domain

If we take a 7 by 7 mean filter in the spatial domain, the corresponding filter in the frequency domain is the sinc function? Is there is a list of filter in spatial domain and corresponding function ...
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78 views

Adaptive Clip Limit on CLAHE

I am working on CLAHE algorithm in order to contrast enhancement. I try to find best clip value to get best result image. However, each input image desires different clip value. Therefore, I need an ...
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25 views

Which frequency filter is it?

To which frequency filter the following operator is equivalent? -1 0 -1 0 4 0 -1 0 -1 In the image domain, it is a laplacian rotated by 45 degrees. In the ...
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51 views

Rotation invariant vs rotation variant

I have a very basic question. We have Rotation invariant filters and filters which are not invariant to rotation. Now let us suppose I want to apply one of these filters. How can I decide which one is ...
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1answer
29 views

What principles to use, in order to create field that will be read by OCR?

I currently have an invoice, where some numbers are written by hand, and I would need to read them automatically. My past experience is that people who write numbers will them write in so many ...
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38 views

How to normalise data for iterative computation of extrinsic camera matrix?

Hartley & Zisserman defend that data normalisation is an essential step prior to the estimation of geometric image transformations. The reasoning behind this, as stated in their book [1, Section 4....
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1answer
20 views

How should I go about cleaning up this kind of images? (algos)

I want to extract text from some images with messy backgrounds. First step was switching to gray scale, applying an edge detection algorithm, and then cleaning up a little bit. Here's an example of ...
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1answer
49 views

Determining parameters of S-function

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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43 views

Performing inverse DFT after taking conjugate of the result of DFT

The following is a question I got in my school assignment. Pick an image and follow the operations Multiply image by (−1)x+y. Compute the DFT. Take the complex conjugate of the ...
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86 views

How to set sigmas and kernels for 3D-Laplacian of Gaussian filters to blob detection in Matlab?

I have written code according to a paper for Lung CT images, but its output wasn't correct. I think it is because of the setting of its parameters. The paper is about a multi-scale method using a ...
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19 views

Which algorithms can efficiently identify rectangular regions in noisy greyscale image?

I have a large number (~50000) of square greyscale images, about 180x180 pixels. I need to efficiently scan them for containing significant block like regions. See the following pictures where I have ...
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99 views

Multifractal analysis of an image using wavelets

I want to measure the fractal character of images using a wavelet approach (if possible) in python. (E.g., maybe things like roughness, anisotropy, or just the fractal dimension - perhaps just ...
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144 views

python: how to compute the color distribution of image in the paper with python and openCV

I am computing the color distribution of image as mentioned in the paper: https://arxiv.org/pdf/1202.2158.pdf. ...
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1answer
26 views

Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
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33 views

MatLab-Finding error in hough line transform

Can I calculate the number of error in Hough Line Transform using MatLab? I did Hough Line Transform process from Canny Edge Detection, but it is unable to detect all the lines. Thanks.
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14 views

Amplifying the difference of luminance between pixels of color images?

I'm doing some research on digital watermarking and came across an article that embeds QR codes on mostly grayscale images and the extraction part for color images is quite confusing the article ...
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35 views

Correspondence between spatial frequency and pixel position

I have a very basic image processing question for which I have not been able to find an answer so far: On several occasions I have encountered descriptions of image filters given in the frequency ...
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15 views

Extracting straight line and curves from an edge image using fourier coefficients

I came across Fourier coefficients and my understanding is that it is very efficient in analysing image properties such as shape etc.. I know we can use Fourier descriptors to describe shape... But in ...
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1answer
72 views

Brightness equalization between different images

I am dealing with a proprietary whole slide image format from 3DHistech, namely MRXS. This image is produced by scanning a glass slide biopsy. The scanner takes pictures at certain positions which ...
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1answer
93 views

How to add additive noise to an image?

I have the following image I and I want to add additive noise using the array N below. Can you please give me a calculation example of how to achieve this? Do I have to move from image space to ...
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17 views

Efficient determination of pixel cluster boundaries

Im looking to replace the values of pixels / pixel clusters in a greyscale image with the average of the values of their boundaries. Suppose the greyscale image is given by $I$ and the pixels to ...
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1answer
29 views

Producing masks from mostly-static-background subtraction when given the background

My data set contains a number of high resolution greyscale images containing a person's face. A single image containing the background without the face is provided. The background is mostly static in ...
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1answer
737 views

What does opencv `mean` function do when passing a mask of zeros?

INTRO I am looking at this project to implement some changes. The project is written in C++ using openCV library. Its goal is to detect cars in parking area to calculate the number of free spots. It ...
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1answer
40 views

How would I fit a distribution to this image noise?

I have collected some noise data from a dimly lit CMOS image sensor. The distribution of pixel values is tallied below:- I'd like to be able to simulate this sensor noise. How would I fit a ...
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22 views

Anisotropic filter implementation wrong?

I've this implementation of the anisotropic filter: ...
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25 views

Extracting overlapping features in an image when individual features are known

Consider this image: Which is a sum of two different sets of features: The first is a collection of overlapping squares with value of 5 and the second is a collection of overlapping squares with ...
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41 views

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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23 views

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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115 views

Improving credit-card-like image scan for OCR

OCR works best for black on white or binary images, where letters have sharp contours, no noise, and solid filling, i.e. they are nothing like this: For the curious it's a part of a document number ...
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1answer
344 views

SSIM(YUV) vs SSIM(Y): values very different

I'm seeing some weird results when trying to compare image qualities in a few different color spaces. Have a look at my graph: I want to compare with another publication, which reported PSNR(YUV) and ...
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1answer
99 views

How to find Performance Ratio (PR)?

If we have one image from BSD (The Berkeley Segmentation Dataset and Benchmark) and for this images Ground truth, how to calculate PR? PR is the ratio of true to false edges and can be calculated by ...