# 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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### Performing DFT twice on an image. Why am I getting an inverted image? [duplicate]

I was asked to perform DFT on an image twice as a part of my school assignment. Why am I getting a blurry inverted image when I perform DFT on an image twice? Sorry, I'm new to image processing and ...
92 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 ...
620 views

### What is different between Euclidean distance and the Geodesic distance?

We have two kinds of distance in image: Euclidean distance and the Geodesic distance. What is different between them? Could you show mathematic formula or visualization to make it clear? The reference ...
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 ...
138 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 ...
180 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. ...
119 views

### Detecting moved and dirty areas between two snapshots/images

I'm new to image processing and trying to figure out best way to identify 'moved' and 'dirty' rectangles between two desktop screenshots.Basically, lets say there is a round circle moving on a screen, ...
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.
174 views

### python: how to compute the sharpness features of image

I am extracting the sharpness features of image as shown in the following image mentioned in a paper. I have done with the following code. Firstly, use the open cv convert the RGB to HSL (luminance ...
35 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.
270 views

### Chroma key algorithm with unknown background color

Suppose that I have an image with a foreground subject and a monochrome background. The image is a real world picture so the pixels belonging to the background do not share the same exact value. I ...
445 views

### python: how to compute the gray level histogram features as mentioned in the paper, and

Hi I am extracting the grey level features of image mentioned in this paper (part 4.5 low level features). "We describe two low level features that are particu- larly important for photo quality ...
223 views

### How do piecewise affine transformation work?

How can piecewise affine transform be used to warp an arbitrary collection of input landmark coordinates to a corresponding set of base coordinates? Can anyone give any physical examples, the book I ...
42 views

### On Human (Face) Detection

There are many face detection and recognition algorithms and APIs out there; however, most of them can produce same results for paintings and avatars as for human face. So, is there any specific ...
15 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 ...
38 views

### Zoom an image with respect to a given image

I posted this question in stack overflow, but I think it is more appropriate here: I have a reference image - 'image_01.png' of size 200x200 and resolution 72 px/in. I have another image 'image_02....
38 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 ...
81 views

### Skeletonization of a Circle - Image Processing

What will be the output of skeletonization of a circle? In my class my instructor said that it will be a single dot in the center but what I found on the Internet was a cross. I discussed with a ...
64 views

### Burst Deblurring algorithm - Understanding the results

I've attempt to implement the algorithm from the paper "Burst Deblurring: Removing Camera Shake Through Fourier Burst Accumulation". The main idea is to take several frames of the same scene, each ...
215 views

### How to approximate gaussian kernel for image blur

From wiki, a $3 \times3$ gaussian kernel is approximated as: $$\frac{1}{16}\begin{bmatrix}1&2&1\\2&4&2\\1&2&1 \end{bmatrix}.$$ Applying this kernel in an image equals to ...
16 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 ...
48 views

### HVS models and rods and cones

It is common to say that the YUV color model is inspired from the human visual system (HVS), knowing that we have many more rods than cones, and consequently, we are more sensitive to light than color....
82 views

### How to get the orientation value of a rotated square?

Suppose we have a square shape rotated by $d$ degrees counterclockwise (or $-d$ degrees clockwise) in a binary image as the following: I'm trying to rotate it by 'Orientation' value of regionprops ...
40 views

### How to resize a Summed Area Table/Integral Image?

There is very clear explanation on how a Summed Area Table/Integral Image works here: https://uk.mathworks.com/help/vision/ref/integralimage.html How to you scale this SAT/Integral Image? For ...
20 views

### Discretized Beltrami energy

In the paper "An Approach Based on Hybrid Genetic Algorithm Applied to Image Denoising Problem", I encounter this fitness function that by minimizing it, a denoised image of a noisy image is obtained. ...
93 views

### Camera Calibration - why do you have to move the calibration board?

I understand the mathematical derivation of Zhang's Method for camera calibration but what I don't understand is why we need to move and rotate the calibration board for several frames in order to get ...
142 views

### Multiple-image dense point cloud reconstruction with camera extrinsics/intrinsics

I have the following data available: Images from different angles X, Y, Z, pitch, yaw, and roll for each camera/image, together with the timestamp Lens distortion parameters and intrinsic camera ...