# 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.

472 questions
16k views

### 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 ?
8k views

### 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 ...
42k views

### 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 ...
20k views

### 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 ...
15k views

### 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 ...
475 views

### 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) ...
299 views

### 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 ...
7k views

### 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 $64 \times 64$?
6k views

### 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?
268 views

### 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 ...
10k views

### 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 ...
24k views

### What does it mean to divide by the standard deviation?

I'm trying to "variance-normalize" an image. In order to do so, I subtract the mean from the pixel value (to have a $0$ mean), and divide by the standard deviation (to have a unit variance) right? But ...
3k views

### Two Quadrilaterals Intersection Area (Special Case)

I have two intersecting quadrilaterals (the area of intersection is the grey polygon with thick boundary): These properties holds: One quadrilateral is always a rectangle There is always some ...
1k views

### any idea what fractal algorithm might generate this shape?

I Found this image around, and i'm curious what algorithm generates this kind of shape In particular, i'm curious how the flow lines are generated, since usually the Mandelbrot iteration just ...
2k views

664 views

### Reprojecting/converting an orthographic image/grid into a cartesian grid

I'm trying to dewarp a fisheye image into a simple rectilinear image of a subset of the fisheye. As part of this, I'm trying to map the azimuth/altitude values into a point on the image. The points ...
914 views

### How do I find/predict the center of a circle while only seeing the outer edge?

Question What formula would allow me to predict the center of this circle? In addition, what attributes of this image must be detected in order to predict the center? I figured understanding the ...
243 views