Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

In general, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame.

0
votes
0answers
3 views

estimation of the ground plane with pinhole camera model

I am trying to understand the pinhole camera model and the geometry behind some computer vision and camera calibration stuff that I am looking at. So, if I understand correctly, the pinhole camera ...
0
votes
0answers
9 views

Otsu Segmentation [duplicate]

I tried to do Otsu Segmentation on this Image But I get this following Result I want to segment that first picture using Otsu Method,so what I want to achieve is the "purple cell" in the center.
1
vote
2answers
56 views

How do you apply a filter after DFT on an image?

Let's say size of the image is 100 x 100 and the kernel matrix is 5x5. I took the DFT of both the image and the kernel. But how do I multiple these two matrices? And which parts involve in these ...
0
votes
1answer
35 views

Bilinear interpolation implemented by convolution

I read the paper Deep Feature Flow for Video Recognition https://arxiv.org/abs/1611.07715. In Sec.3, the author implements bilinear interpolation like this: $$f_i^c(p)=\sum\limits_{q}G(q,p+\delta p)...
0
votes
1answer
13 views

How to add additive noise to an image?

I have the following image I and I want to add additive noise using the array N below. Can you please give me a calculation example of how to achieve this? Do I have to move from image space to ...
0
votes
1answer
31 views

How to get general projection of rect function?

To be more clear I want to get a general expression for PƟ(t)= ∫∫rect(x)rect(y)δ(xcosƟ+ysinƟ-t)dxdy I also want to find particular projection for Ɵ=0 and Ɵ=45 and also Fourier Transform of the ...
0
votes
0answers
52 views

2D Signal Properties of Fourier Transformation [closed]

I was asked this question below. I have to match i-v to a-j (matching could be one to many or many to one) and i should prove the matchings. If conjugation is not made, i can assume that $h(n_1,n_2)$...
1
vote
2answers
47 views

Check whether a given equation is linear

$ a = (x, y) \in \mathbb{Z}^2 $ is given as a pixel. My equation in which $g$ is image(matrix) is defined as, $f(x, y) = 56g(x,y)+93g(x−1,y)+92g(x+1, y)−57g(x, y−1)+555g(x, y+1) $ How can we know ...
0
votes
0answers
14 views

How to obtain backprojected distribution?

I want to show that backprojected distribution , $f_b(r)$ , obtained by backprojecting the projections of the impulse function $\beta(r)=\frac{\delta(r)}{\pi r}$ is equal to $\frac 1r$. I figured out ...
0
votes
0answers
8 views

Deciding the patch size for training discriminative classifiers in object tracking

Object Tracking-by-detection methods work by training a classifier on the patches sampled around the predicted target location in the current frame, and using the classifier to predict the location in ...
-1
votes
0answers
7 views

what are the image processing algorithms Used for OCR on binary images(optical character recog)?

I am working on a binary(black & white) images, because of several constraints i thought of dropping Learning based methods for OCR. As the binary image contains text info. Image segmentation ...
0
votes
1answer
25 views

How can I trace a path around an image consisting of only black and white lines?

I'm looking for a way to trace a closed curve (i.e. a long list of pixel values all connected by lines in between) that approximates a bitmap image of black and white lines. The image starts out as ...
1
vote
1answer
40 views

How to represent impulse function in 2D?

To be more specific I want to show that impulse function in 2D can be represented as $β(r)=δ(r)/πr$. Also I want to show that each projection of a two dimensional impulse function at the origin is a ...
-1
votes
0answers
28 views

Functioning of Pre-processing blocks in image processing

Can anyone please explain that why do we need to preprocessing block and what is the importance of each block in preprocessing stage in image enhancement ?
1
vote
1answer
32 views

Why delete high frequence in fft return the area of the most changes?

I'm new to ||image-processing|| and || fft filters || I have a relative smooth $\mathtt{2D}$ (circle) gaussian surface (height $10$) with several "holes" in it, and the surrounding area [has] some ...
-1
votes
0answers
18 views

Feature preserving image downsampling

How can an image be downsampled without losing its features?. Let's say there's a $1000\times 1000$ green image with a small $5\times5$ red dot in the middle, I want to downsample the image to $100\...
0
votes
1answer
14 views

What do the Contour Levels Produced by Matlab Function Contourc Represent

I have been trying to understand what the contour levels are. As far as I understand a contour of the function $Z(x,y)$ is a set of points in the $(x,y)$ plane, such that $Z(x,y)$ is fixed at some ...
0
votes
0answers
12 views

Difference between morphological gradient and derivative of 1-D signal

What is the difference(s) between morphological gradient and derivative of 1-D signal (x(t))? Thanks in advance.
1
vote
0answers
18 views

“Image Processing” [closed]

I'm an Italian student. I'm studying Gnu Radio and I would like to upload a photo, can I upload it with "file image source" or other blocks? I need to make FFT of an a image. -> image 2D Thank you ...
5
votes
2answers
820 views

Why should an image be blurred using a Gaussian Kernel before downsampling?

I recently read that before downsampling an image, it should be blurred using a Gaussian Kernel. This way, the downsampled image is better than just picking a single pixel out of a NxN block or ...
0
votes
0answers
23 views

Expressing a square as product of rect functions

A square is centered at origin and length of one of its side is 'a' units. In terms of rect functions, such a square can be expressed as product of two rect functions, i.e., $f_a(x,y) = A [rect(mx)] ...
0
votes
0answers
14 views

Efficient determination of pixel cluster boundaries

Im looking to replace the values of pixels / pixel clusters in a greyscale image with the average of the values of their boundaries. Suppose the greyscale image is given by $I$ and the pixels to ...
0
votes
1answer
65 views

Basic confusion about the DFT and convolution

I am learning DSP (with Digital Images) and I have some elementary confusion about the convolution between two discrete periodic signals. Specifically, I have learnt that when filtering an image, we ...
0
votes
0answers
13 views

Readjusting the LSB encoded pixels in Edge Adaptive Steganography

I have two pixels generated using LSB encoding $(x_{i}^{'}, x_{i+1}^{'})$. However, there are chances that either one of them, or both, lie outside the range $[0, 255]$ or $|x_{i}^{'} - x_{i+1}^{'}| &...
0
votes
1answer
33 views

Edge detection in a crack pattern image

Here's an image of a cracked pattern. I wish to convert it to binary image where the continuous crack lines form the only discernible pixels. The main problems I am having in the lack of uniform ...
0
votes
0answers
64 views

How to calculate Total Variation (TV) of two images?

I try to implement Differential total variation (DTV) as described in (Wu, Y. et al 2017) or (Li, Y. et al 2015) to find the similarity measure between two images. (Li, Y. et al 2015) describe DTV as ...
1
vote
1answer
27 views

Entropy of an image with equalized histogram

Let's suppose we have an image and perform histogram equalization on it. Would the entropy of the resulting image be lower, higher or equal than the entropy of original image? At first I tought that ...
1
vote
0answers
31 views

Excluding points too close to a set of coordinates

I was wondering if anyone can help me. My ultimate aim is to take an image like the one shown and draw line between the white and black blobs that show a direction and output the coordinates in the ...
0
votes
0answers
14 views

Edge adaptive steganography

I am trying to implement an IEEE paper based on edge adaptive steganography. For that I have to convert a $m \times n$ resolution image to a row vector by raster scanning. Then I have to take two ...
0
votes
0answers
5 views

what's gray level features and how to compute it with python

Hi I am a new one to computer vision. now I am trying to classify the image into good or bad based on image features. Now I want to use the features in the following paper: https://arxiv.org/pdf/1202....
0
votes
1answer
29 views

What is the meaning of the sum of kernel components in digital image filtering?

When analyzing an image signal as a series of Dirac impulses in the continuous spatial domain, I applied continuous low pass filters (to reconstruct or smooth it) with area equal to 1 to preserve the ...
-2
votes
2answers
44 views

Image processing - Why is sum of values of a blurring filter = 1?

Usually, blurring filters have the sum of all the values in the filter matrix equal to $1$. Why is it so?
0
votes
1answer
22 views

How to draw a vector between light and dark spots on an image

I'm very new to Python and I need to draw vectors between dark and light spots on an image. Ive managed to convert it to greyscale but I'm struggling with identifying the dark and light spots. If I ...
1
vote
1answer
23 views

Fast morphological erosion/dilation with variable window sizes

I want to perform the following operation on an image: consider a square window around every pixel, find the maximum value in this window, and replace the central pixel value with this maximum value. ...
1
vote
2answers
63 views

Why are edges in spatial images represented as edges in their Fourier transform image?

Here is a well-known image and its Fourier Transform (magnitude). If I understand correctly the theory behind the FFT, each pixel in the FFT image represents a certain 2D sine wave with frequency ...
0
votes
1answer
26 views

Is this statement contradicting with the band-limiting theorem?

The following sentences are from the footnote of page 240 in R.C. Gonzalez's Digital Image Processing (3rd): An important special case is when a function that extends from -Inf to +Inf is band-...
1
vote
0answers
14 views

Relation between variance of gaussian noise and intensity variance in Bilateral filter

So I implemented the code for bilateral filter from here and ran it for various values of spatial sigma and intensity sigma. I noticed that when I add gaussian noise to an image with variance say 0.02,...
0
votes
1answer
21 views

Producing masks from mostly-static-background subtraction when given the background

My data set contains a number of high resolution greyscale images containing a person's face. A single image containing the background without the face is provided. The background is mostly static in ...
1
vote
0answers
11 views

converting digital length to physical length using reference object

I am trying to find actual length of an object, say X, from an image. For that I'm using a reference object , say Y, ( object of known dimensions ). From image while converting pixel length of X to ...
0
votes
1answer
54 views

Correlation between slightly misaligned images

I am matching camera images of projection screens with rendered pages of PDF documents using Pearson's and Spearman's correlation coefficient. When the images (3, 4, 5) are aligned, this works fine in ...
1
vote
0answers
24 views

What is a basic method to segment “dark blobs”?

I'm new to image processing, but I have good knowledge of general data processing. Could you please suggest an approach which can be used to segment images like this? I suppose it is some kind of ...
1
vote
0answers
22 views

Detection of interesting structure in images?

I'm looking for methods of computing some measure of structure in an image. (I do not have a rigorous definition of "structure" though........) Consider the 15 image blocks below: Suppose for each ...
0
votes
0answers
40 views

apply 2x Gaussian filter and then down sample by 2 an one dimensional input, choose parametric sigma to not miss so much information

Please consider a 1-dimensional signal as an input. What are the considerations in choosing $\alpha$ if two Gaussian filters each with parameter $\sigma = \sqrt{\alpha}$ are applied in cascade and ...
1
vote
2answers
36 views

What fps can be considered as a hardline for real-time performance? Is there any academic paper that describes this?

I am trying to design a deep learning based inferencing solution for security applications. My deployed program achieves an FPS of 15fps for classification. Can it be considered real-time?
2
votes
1answer
35 views

Sobel and Prewitt operators decomposition

I was reading in the wikipedia page of Sobel operator and Prewitt operator that is possible to decompose these two operators (quote form the Formulation paragraph): "as the products of an ...
3
votes
1answer
63 views

What's logic behind the constuction of Sobel's filter in image processing?

I am basically very new to this image processing field. I am presently working on edge detection on colour images. While learning the basics of edges and edge detection in images, I encountered image ...
0
votes
0answers
42 views

Difference between 2D image resampling and 1D signal resampling

I implemented a rational resampler for 2D bitmap images by the following steps: Zero-stuff to interpolate Low-pass filter to remove high frequencies introduced by zero-stuffing Low-pass filter to ...
1
vote
1answer
760 views

Removing noisy lines from image - opencv - python

I want to process different type of image to extract actual text from noisy image .I am using open cv to do this job it is working fine but the problem is I need to set different lower threshold to ...
0
votes
0answers
15 views

What is the best way to overcome color mixing limitation?

I'm doing image processing using c++ and openCV to process color. Color mixing method (addition and subtract), when you try to do it in computer with RGB system, colors will have some value (0-255). ...
0
votes
0answers
40 views

What does opencv `mean` function do when passing a mask of zeros?

INTRO I am looking at this project to implement some changes. The project is written in C++ using openCV library. Its goal is to detect cars in parking area to calculate the number of free spots. It ...