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.

This tag is for mathematical questions about the field of image processing. Note: programming issues related to image processing belong on other Stack Exchange sites: Stack Overflow, Signal Processing or Computer Science.

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What do eigenvalues have to do with pictures?

I am trying to write a program that will perform OCR on a mobile phone, and I recently encountered this article : Can someone explain this to me ?
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Mathematical explanation behind a picture posted (lifted from facebook)

In this image given below, there is an actor's (famous south Indian actor Rajinikanth) image which can be seen only if you shake your head ! I had lifted this from Facebook. I am just curious to know if there is any mathematical explanation for it.…
Rajesh D
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What does the Fourier Transform mean in the context of images?

This is clearly a very important equation with tonnes of properties that I see come up a lot in image processing literature, but I don't understand why this equation is important, and what it is saying. What does it really mean and why is the…
water
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What is divergence in image processing?

What is the difference between gradient and divergence? I understood that gradient points in the direction of steepest ascent and divergence measures source strength. I couldn't relate this to the concept of divergence in image processing. What is…
Premnath D
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Laplacian 2D kernel - is it separable?

I'm wondering if the 2D laplacian kernel 0 1 0 1 -4 1 0 1 0 is also a separable kernel. How can I find that out?
paulAl
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How to measure the irregularity of a hexagon?

I need to evaluate the quality of a list of machine parts, which roughly has one center point surrounded by 6 exterior points. If the quality is good, then the 6 exterior points will form a regular hexagon and the center point will locate in the…
Wei Feng
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What are the limitations /shortcomings of Fourier Transform and Fourier Series?

I am fond of Fourier series & Fourier transform. But every approach has some outcomes and some shortcomings. It's limitations lead to innovation of new approach. So, can anybody explain about The limitations/ shortcomings of the Fourier…
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How can I combine affine transformations into one matrix?

So from what I understand from this picture, the box is stretched to twice its width. And it is then flipped from the x-axis. And then it is rotated 30 degrees anticlockwise. So these three transformations are Scaling, then Reflection then…
Ogen
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How to mark rational points on a sphere

I found this picture on mathoverflow, which I find very intriguing and so I like to know how to draw such an image with a simple computer program. To calculate the rational point, I can draw a line from P_0(0,0,1) and P_1(u,v,0) and calculate the…
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Homotopy and watershed

homotopy is a new word to me. Upon trying to understand this property, I immediately think of another well-known segmentation algorithm: watersheds. I see that watershed should exhibit some homotopic properties. In fact, I've also located a paper…
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A mathematical way to represent an image kernel?

How to represent the calculation in this image mathematically? For example: With the discrete convolution and Fourier Transform. It tries to do a calculation on the original image (image $A$/input) and save the result of the calculation in image…
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Why is $8 \times 8$ matrix chosen for Discrete Cosine Transform?

In JPEG and MPEG, why is $8 \times 8$ matrix chosen for Discrete Cosine Transform? Why not any other, say $64 \times 64$?
user9476
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Algorithms to increase or decrease the contrast of an image

While tinkering with image editing, I thought I might implement a contrast algorithm; something that would take a range of values and, based on the value that the user provides (from 0 to 255; the range of a byte) the contrast will be decreased or…
person27
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Image Reconstruction:Phase vs. Magnitude

Figure 1.(c) shows the Test image reconstructed from MAGNITUDE spectrum only. We can say that the intensity values of LOW frequency pixels are comparatively more than HIGH frequency pixels. $$ f(x,y)= ∑_(u=0)^(U-1)∑(v=0)^(V-1)\ |F(u,v)|…
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Least square fit of ellipse worsens with increasing border thickness

I use the least square method to fit ellipses to data points that originate from a binary image. The least square fit minimizes the sum of squared algebraic distances between data points and the closest point to a non-centered, rotated ellipse. For…
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