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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CT Slices to Planar XRay
I have axial slices of chest CT scans. Now, I want to use all these slices to construct a planar structure like an X-ray with a coronal view (Posterior to Anterior or Anterior to Posterior view).
I ...
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3answers
64 views
Reversing the Order of Operators for Edge Detection?
Usually, for edge detection, we perform smoothing and then pass it through difference filter. What if application of difference filter happens first and then smoothing. How the math behind the same ...
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1answer
26 views
Is it okay to interpolate between overlapping areas obtained using a sliding window?
I am using a 50x50 pixel sliding window which moves left to right every pixel so that it covers a whole binary image which is about 2000x2000 pixels. In the window, the ratio value of black to white ...
3
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1answer
31 views
How does DCT decorrelate images?
I've read in multiple places that DCT decorrelates Toeplitz matrices and images usually have Toeplitz structure. Can you explain with an example how DCT decorrelates a Toeplitz matrix?
Example for DFT:...
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2answers
66 views
1D DCT matlab code
I was writing MATLAB code to compute 1D DCT of sample y.
On computing DCT for y=[0,1,2], code generates coefficient ...
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2answers
39 views
How Does Color Conversion and Downsampling work When JPEG compressing a grayscale image?
For color images I know you have to convert to YCbCr format, and then for downsampling is based on the fact that human beings see differences in Y more than differences in Cb or Cr.
How do I do these ...
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1answer
25 views
Intuition about tag pose estimation accuracy
I have some difficulties to have a correct intuition about expected pose accuracy when dealing with planar pose estimation (e.g. pose estimation from AprilTag detection) and perspective camera model.
...
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1answer
28 views
What Is an Oriented Gaussian Second Derivative Filter
In the paper: Detecting and Localizing Edges Composed of Steps, Peaks and Roofs, the authors refer to an image filter as an oriented second-derivative Gaussian filter. I'm trying to figure out what ...
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24 views
How to plot ROC Curve of feature detecttion algorithm? [closed]
I want to compare the performance of feature detection algorithms like Harris, Shi-Tomasi, MSER, ORB, FAST, BRISK and KAZE using ROC Curve. I found that I need TP rate FP rate. How do I derive the TPR ...
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2answers
19 views
MRI K-space to image: why track frequencies in two dimensions?
While trying to better understand how an MRI goes from k-space to an image, I came across this wonderful website that explains how you would represent an image as a collection of rows of pixels where ...
2
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3answers
145 views
What does this paragraph mean?
I'm reading this paper about about an algorithm to measure image sharpness, and am confused by these sentences in the 6th paragraph:
It is well known that the attenuation of high-frequency content ...
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1answer
21 views
What is Bottom-Hat transformation?
I am reading the Digital Image Processing book by Gonzalez and i can't seem to understand Bottom-hat transformation. Can anyone explain it to me in easy terms?
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1answer
28 views
Selecting a Digital Signal Processor for a Specific Image Sensor
I am working on developing a camera and I am trying to select hardware for the camera. I believe that I may need a digital signal processor to compress image data before it is transmitted to a ...
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1answer
38 views
Detect lines transitioning to blobs in images
I have the following images (in high resolution, uncompressed). When the process starts, the left image is displayed and it ends something similar to the right image.
The first image shows labyrinth-...
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0answers
15 views
Standard Deviation of Character Gradients in a Document Image
I have the paper titled "CG-DIQA: No-reference Document Image Quality Assessment Based on Character Gradient". It is all about assessing the quality of the document image based on its blurriness. To ...
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0answers
109 views
Algorithm that Fills the White Holes Within the Character Image
I have this degraded image :
Using paintbucket tool in Paint.NET Windows application, I fill the character image black.
My ...
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1answer
17 views
Noise problem when transforming and quantizing difference between images
I have a program which does forward and inverse DCT and quantization and dequantization using JPEG matrix. If I apply it to a single image it works fine, but if I try to apply it to a difference ...
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1answer
16 views
Bilinear Interpolation on A Subsection Of An Image
Is it possible to do bilinear interpolation on each 8 by 8 block of an image one at a time until you cover the entire image rather than doing it on the entire image? What are the consequences of this?
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23 views
Compressing sparse vectors based on compressive sensing
I have a sparse vector $x$ of size $N$x$1$ which is sparse with number of non-zeros values are $m$, it means $m$ out of $N$ values are non-zeros, the non-zeros locations are distributed randomly.
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21 views
security in biometrics
I read the following in one of the research papers:
Cancelable biometrics using random projections can be implemented by multiplying a random matrix with a feature vector. The result is a cancelable ...
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0answers
34 views
What is the gradient of fft?
I have a time-series of length N generated by the following equation:
...
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0answers
12 views
Computing White Speckle Metric in a Document Image
The paper 'Metric-based No-reference Quality Assessment of Heterogeneous Document Images', discusses about measuring the quality of characters in a document image. I'm having difficulty to understand ...
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1answer
22 views
What happens when you wrap a 3x3 kernel at the corners of an image?
I am puzzled by what actually happens when you process border cases when applying an image filter. For instance if I apply a 3x3 Gaussian kernel to the top left pixel[0][0], the remaining pixels that ...
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2answers
45 views
Understanding zero-phase filters
I'm reading the book "Digital Image Processing" by Gonzalez and Woods and I'm wondering how their definition of zero-phase-shift filter is equivalent to the one given here.
"Digital Image Processing" ...
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2answers
58 views
Binary image? Only black and white? [closed]
By name, a binary image is one that has two levels. But is it essential that those two colors are black and white? Or any other combination also allowed as shown in attached snap. Snap is output image,...
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1answer
28 views
Advantages and disadvantages of multiplying sparse vector with sparse matrix
Assume I have a sparse vector $x$ whose few values are non-zeros, that vector is multiplied with sparse unitary matrix $Y$ giving $z = Yx$. Are there any advantages of detecting the sparse vector $x$ ...
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1answer
37 views
Zero-phase-shift filters must be symmetric about the origin
In reading Rafael Gonzalez Digital Image Processing, second edition, section 4.10.2,
the author writes:
Notch filters are the most useful of the selective filters. A notch filter rejects (or passes)...
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3answers
91 views
What is the DFT of a binomial filter?
I hope this question is not too simple, I just started learning digital image processing. The 1D binomial filter of size 2 is defined by $B_2 = \frac{1}{4}\begin{bmatrix}1 & 2 & 1\end{bmatrix}$...
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What is Maximally Stable Extremal Regions (MSER)?
In the paper , MSER is being defined. Please help me understand what is MSER and how to implement it.
The paper says,
The regions are defined solely by an extremal property of the
intensity ...
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1answer
11 views
Comparision between SSIM and MAD Image Quality Assessment Algorithms
I have been working with Most Apparent Distortion(MAD) tool to evaluate the quality of images. I have read a paper that compares SSIM, PSNR, FSIM, etc. with MAD. I am uncertain about some calculations ...
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0answers
61 views
Reconstruct signal from imprecise sampling?
I'm trying to digitize a VGA signal with a low-power consumer computer running a consumer OS and am having issues with the stability of the sampling rate.
What I did so far:
grabbing the green ...
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2answers
53 views
What does it mean to rotate an image by 0.1 degrees?
In the old Tangent Prop paper (you don't need to know this paper), the tangent vector of the rotation transformation (think of this as a vector-valued function) at some input image is approximated by (...
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17 views
Smoothing jagged lines in an image?
I have an image like this - I would like to smoothen the lines in this (as you can see they lines are a little jaggy.) How can I do this?
I obtained the lines by isolating them from another image ...
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1answer
29 views
Image Processing [closed]
I have an image and I am trying to find its rows and columns.
A = imread('lena.jpg');
nrows = size(A,1)
ncols = size(A,2)
This is 3 dimensional matrix. Output ...
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1answer
33 views
Justification for Squared $ {L}_{2} $ Data and Smoothness Term as an Error Bound
Often in variational methods (and not only) we have an energy that is of the form:
$$E(u) = \frac{1}{2}\|f-u\|^2_2 + \frac{\alpha}{2}\|\psi(u)\|^2_2,$$
where the first term is referred to as the data ...
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1answer
12 views
Questions in a Character Degradation Model Paper
I have questions in the ‘Noise region definition’ and ‘Noise generation process’ of the paper “A character degradation model for grayscale ancient document images”.
In Noise region definition, ...
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24 views
How can I stitch bottom of some image to topside of another image by erasing as much overlapped image as possible?
I have 2 images of size 1920*1080 and I want to try image-stitching on them. These are images (images are from wind turbine blade.)
This is the first image
And the second image.
I already have ...
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21 views
What is the difference between template matching and object detection?
What is the difference between template matching and object detection? Is the only difference that the template is typically rectangular while the objects can be of any form (including rectangular)?
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22 views
How to know what kind of noise?
Im working with friends on a computer vision project for university. For the preprocessing part we are going to use a Gaussian filter. One of my project partner said I have to justify the use of a ...
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0answers
59 views
Is rotation of a Fourier transform the same thing as Fourier transform of a rotation?
I'm working on an image processing problem and wondering if DFT(rotation(image)) == rotation(DFT(image)) (1). My final goal is to apply rotations in the Fourier domain then do an inverse Fourier ...
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2answers
32 views
Average image over $N$ frames with one frame buffer
Can you give some filter that is averaging an image over $N$ samples in a recursive way that only needs one frame buffer?
$\frac{1}{N} \sum_{k=1}^{N} y_{k}(m,n)$
I can only imagine filters that need ...
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0answers
56 views
Mapping ring asteroids in Elite Dangerous by image processing
In the game Elite Dangerous, which is an online spaceflight-based sandbox game set in a procedurally-generated galaxy, one of the most profitable in-game occupations is mining commodities from ...
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2answers
29 views
Downsampling Image
Can you suggest me a good downsampling algorithm for an image. I explored area averaging method, but I am looking for better. I am using good in the sense that it should be less computational ...
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0answers
19 views
Gaussian filter vs median filter vs wiener filter??Noise tackling performance with image corrupted with salt and pepper noise
I am trying to remove noise in an image usig three different filters,but i am bit confused in output performance of each filter. I think gaussian filter has best performance in this case(please guide ...
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0answers
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How to implement a single shot object detector with only “one” anchor box per feature-map cell
I am newbie to SSD model, I have some images of products on a shelf , I trying to detecting that products using SSD with one anchor box per feature map, please help me out, how to prepare the data and ...
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1answer
35 views
Confusions regarding meaning of “kernel” in signal processing and image processing? [duplicate]
While studying filters in DSP and DIP, the term "kernel" is often encountered
What is the meaning of "kernel" in context of filters??Please kindly explain in simple words with an example
I have also ...
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Learn the relationship between the pixels in a chunk of an image and then search for more chunks like this one
I've just started to learn computer vision and I have a doubt about if I can do the following and how can I do it.
If a 4x4 square of the image is like this one:
Here I want to detect another chunk ...
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Building a spatio-temporal filter
I want to implement a spatio-temporal filter for my images which are a set of silhouettes of a cycle of walking. So I gather all the images in an array and convolve the 3D array with my spatio-...
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2answers
52 views
Confusions regarding frame rate?
We know that when many image are shown in succession they create illusion of video
But what is the minimum rate of frame/images so that still images appear as video?
In this case, images/frames are ...
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1answer
21 views
change in size of an individual pixel? [duplicate]
If we want to change resolution of an image,we can achieve that by increasing or decreasing the number of pixels
Is there any other way ? Can we change dimensions of an indvidual pixel,rather then ...
