# Questions tagged [image-processing]

This tag is for the mathematics involved in the field of image processing. Many such questions are also appropriate for Signal Processing Stack Exchange.

214 questions
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### When is a mapping the proximity operator of some convex function?

Sorry for cross-posting from MO. It's been a few days and the question hasn't received any attention there. So, is there a characterization of mappings $p : \mathbb R^n \rightarrow \mathbb R^n$ which ...
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### Compute real length from perspective

Given the two green lines and the real distance between them (blue lines), is it possible to calculate where in the picture would be placed a point 4.5m away from a certain initial point (red line)? ...
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### Multiphase levelset Chan Vese algorithm

I am implementing the multiphase level Chan Vese algorithm. I am using IPOL document as reference (http://www.ipol.im/pub/art/2012/g-cv/article.pdf) Everything is clear for me, except the stopping ...
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### Detect clusters in an RGB space

With OCR one of the first stages in a processing pipeline is to accurately identify what is print and what is paper, generally achieved by some form of binarization. In the good old days most scans ...
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### How to deblur a image matrix blured by two circulant matrix?

We suppose an image matrix $X\in \mathbb{R}^{n_1\times n_2}$ is blurred by two circulant matrices $\Phi_1 \in \mathbb{R}^{n_1\times n_1},\Phi_2 \in \mathbb{R}^{n_2\times n_2}$. We can observe the ...
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### Increasing the accuracy with techniques of interpolation

I am currently pursuing my Masters in electrical engineering and the class I am taking is Image Processing. Last night my professor introduced an interesting idea of ways of "guessing" the color of ...
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### Aligning image contour to map coordinates - ways to solve?

Got an exotic problem I guess, but still. Let's say, I have an random image contour, created bu Laplace or Sobel algorithm. Also - I have a random set of coordinates (pretty dense one for example). ...
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### How to arrange these detected points from one end points to other, edge to edge of an object?

Please suggest what topic to tag this question if I have tagged it in the wrong topic, after going through this. I have detected partial edge of an object like this after image processing. I have ...
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### How to do 3D reconstruction using matched points (with stereo images)?

I have 2 images, called left and right images. I have some matched points $[c_l,r_l]$ and $[c_r,r_r]$ in both of them (these points are in pixel coordinates). For a 3D point in the real world, they ...
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### calculating the effect of a point-spread function in the frequency domain

If my point spread function looks like: h(x) = 1, |x| <= W (where W is a positive integer) 0, |x| > W then i want to measure how it would effect the frequency content of some function f(x),...
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### Calculate the height of a person on a picture

I am experimenting with an app to calculate the length of a person with the camera of my phone. I put my phone on the ground against the wall and make a picture. This situation is shown in the image ...
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### Change of basis from RGB to different set of colors

Color images are defined by red, green, blue (RGB) values at each pixel. What if instead I wanted to define pixel colors by orange, black, and yellow? Is there a way to change the basis of colors from ...
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### Relation between focus and camera intrinsic parameters

Does a focus tuning affect the camera intrinsic parameters? More precisely, if the focus of a camera is changed, does the camera intrinsic parameters matrix remain unchanged? Apparently, since this ...
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### Derivative of an Euclidean-Vector norm.

Consider: x a $N \times 1$ vector , with elements $x_i$ b a $N \times 1$ vector , with elements $b_i$ A a $M \times N$ matrix , with elements $a_{ij}$ ( Symmetric matrix - Block Circulant ) As we ...
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### Math behind Photoshop's gradient tool

I want to implement something like Photoshop's gradient tool and I need to understand the math behind it. Can anyone explain the differences between linear, radial, angle, reflected, diamond gradients?...
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### 2D Discrete Fourier Transform on an Image - Example with numbers (rgb)

I am trying to write my own function that takes an image, an pixel by pixel it calculates that pixel value that will produce a 2D Fourier Transform image. I have no idea about signal processing, my ...
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### Eigenvalue and informations?

I have been wondering about this these last couple of days and cannot seem to understand how come this is the case.. I know about the eigevalues and the eigenvector, and that it can be found on for ...
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### Homography matrix form for decomposition

I am trying to decompose a homography matrix. I read that there are a few methods to do that (e.g. Faugeras, Zhang). But I wasn't able to produce a useful output yet. I am not sure which form my ...
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### Understanding JPEG compression.

I have some problems in understanding a passage of the JPEG compression algorithm: Consider an $8\times8$ matrix $M$ that in our case is a "piece'' of a channel (for example the red channel $R$) of ...
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### Distributional Representation of Perimeter in Chan-Vese

While re-implementing the classic Chan-Vese Algorithm for image segmentation, I stumbled upon the following statement, which I have problems to understand: Let $H: \mathbb{R} \to \mathbb{R}$ be the ...
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### What is the difference between Bilinear interpolation and Bilinear filtering

I'd like to know that different between bilinear interpolation vs blinear filtering in the manner of image processing warp operation. Are those two operations are identical ? I try to sample a ...
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### Euler Lagrange equations

I need to minimise $$\int\limits_\Omega|\nabla H_\epsilon(\phi)|\,dx\,dy$$ with respect to $\phi$. Where $H_\epsilon$ is the regularised Heaviside function, so that it is differentiable. This can be ...
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962 views

### Area optimization: Packing rectangles inside rectangle

Background: I am scrambling to figure out the optimization algorithm to build sprite image, which is essentially a big container rectangular image, with multiple rectangular images. I have found an ...
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### 2-D DFT of a matrix PxP and 1-D DFT of a vector of size P^2?

What is the difference between the following two things: make a 2-D Discrete Fourier Transform of a certain matrix A[p,p], first reshape this matrix into a 1-D vector a[p^2,1], and compute the 1-D ...
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### Calculating the aspect ratio of the rotated rectangle on the image

I need to determine the aspect ratio of the rectangular object (such as mobile phone or credit card) on the image. The problem is that the object might be photographed from an angle or perspective. So ...
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### Projection Slice theorem getting rid of artifacts?

I have employed the fourier(projection) slice theorem in matlab. I have a 3D image, P(x,y,z) defines their pixel intensities at a given location int he image volume, it is discrete and uniform. I ...
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### Singular Value Decomposition

I want to decompose an image $A$ using the Discrete Wavelet Transform and then find the singular values, $S$, such that $A=USV$. I will then do the same to another image such that $B=USV$. I will ...
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105 views