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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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 ...
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800 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 ...
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How would I fit a distribution to this image noise?

I have collected some noise data from a dimly lit CMOS image sensor. The distribution of pixel values is tallied below:- I'd like to be able to simulate this sensor noise. How would I fit a ...
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118 views

Improving credit-card-like image scan for OCR

OCR works best for black on white or binary images, where letters have sharp contours, no noise, and solid filling, i.e. they are nothing like this: For the curious it's a part of a document number ...
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1answer
103 views

How to find Performance Ratio (PR)?

If we have one image from BSD (The Berkeley Segmentation Dataset and Benchmark) and for this images Ground truth, how to calculate PR? PR is the ratio of true to false edges and can be calculated by ...
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1answer
122 views

Redistributing Color in a RGB Image According to a Gaussian Distribution

I haven't done this stuff in a while. If I have an image $I$ I can equalize the histogram of the image using some opencv procedure, it's already defined. Equalizing an histogram means essentially to ...
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16 views

Quantization of Image which have taken from partially less dark

I have picture with high resolution with 20M memory space and this image has been taken from the standing away from the window in room which has significantly less light as compared to outside. Image ...
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50 views

Scan an Auditorium, Count People, and Display Open Seats

I'm looking for any recommended approaches to be able to digitally process a room full people, like an auditorium or a movie theater and output the following information: Goals: How many people are ...
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92 views

How to obtain the relative position (coordinates) of SIFT feature from image center coordinates?

I have extracted SIFT features (keypoints and descriptors) of training set and saved in an inverted index form. My question is how can I calculate the coordinates of each visual features in an image ...
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84 views

how to describe the color of a small image patch?

I want to describe the color of an image patch (say of size 5x5) centered around a pixel of an rgb image. The most straightforward way to do that is to calculate the average color over that patch and ...
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256 views

Programming the IDWT for image processing

I want to program the 2D inverse discrete wavelet transform (only 1 level) in the case of image processing. In the matlab website there's this diagram: now, I want to program the IDWT with haar ...
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78 views

How to overcome effect of intensity variation in image processing?

I want to process an image for which I need the method to be robust to lighting conditions. For that the only thing I can think of is normalising intensity. I did this by dividing the image with ...
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1answer
116 views

wavelength / RGB valve per pixel

Preamble: I want to stress that I don't know anything about photo-editing or signal processing. But I am a composer who happens to be working on a project in which sound / light overlap. Question: Am ...
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452 views

Convex hull area in pixels

I am calculating different attributes for connected regions of the image, with the final goal of classification. One of the attributes I am working with is a sparsity measure, calculated as the ratio ...
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1answer
426 views

The Kernel in the Guided Image Filter

I am trying to understand how to calculate kernel matrix for guided image filter. Following is the formula for kernel calculation. where k is window withing pixels i and j belong i assumed that ...
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35 views

Simple technique to segment out optical disk and vessels from retinography

I'm looking for simple techniques to segment out the optical disk and vessels from a retinography. By simple I mean using techniques taught during an introductory course on Digital Image Processing. ...
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180 views

How doesn't JPEG huffman table contain 256 codes?

Here are the DHT entries I got from JPEG snoop: ...
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31 views

Kalman Filter - Gaussian representation

I'm trying to understand well the kalman filter, as a result i'm having this question : Why do we represent noise with a Gaussian ? what does this really mean intuitively ?
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485 views

How can l extract characters withe same bounding box size?

l have a set of images which represent a sequence of characters. l'm wonderning whether OpenCV can segments and crop each character from the image with same bounding box size. My numbers are not ...
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108 views

How to distort a signal (image) pattern using bilinear interpolation

I have a signal pattern $s$ that generated at time $t$ like this: $$ s(x,y,t)=D(x,y)\sin(\omega t-0.56) $$ Where $D(x,y)$ is a mode shape, calculated by $$ D(x,y)=a\left\{\left(\frac{x}{m}-0.55\right)...
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41 views

Looking for a file format for lane detection

I am trying to extract lane boundary lines from two recorded video cameras on the sides of the vehicle. I would ultimately like to calculate lane position from those boundaries. My thought process is:...
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Question about central spatial moments

Spatial moment $$ m_{pq} = \sum_{(x, y)\ \in \mathbb R} x^p y^q I(x, y) $$ The order of each moment is $p+q$. Central moment $$ \mu_{pq} = \sum_{(x, y)\ \in \mathbb R} (x - \bar x)^p (x - \...
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224 views

How can I properly detect a ball moving in a film capture?

I have problem in detecting a ball moving in a flume (image below). since converting the frames into grayscale format didn't work I converted it into rgb and make it more saturated. problems are: 1- ...
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2answers
938 views

Segmentation of warped text lines

I am trying to segment warped text lines found in photos taken from a page of a book (from the camera of a smartphone). This is meant as a preprocessing step before running OCR on them. I have found ...
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440 views

Segmentation and edge linking

I am trying to implement segmentation on an image. after a difference of Gaussians Process and applying weights to my edges I want to go through edge linking by local processing. I have seen this ...
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1answer
137 views

Image Processing- ornament detection

So I am working on a project where we are supposed to detect and count the red and gold ornaments in the picture provided in the link below. I am having issues detecting and counting each ornament and ...
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449 views

Image reconstruction using Laplace pyramid

Given a sub-sampled Image $P_n$ belonging to layer $n$, a Gaussian kernel $G$ and a Laplace Layer $L_{n-1}$ of layer $n-1$, my efforts to create $P_{n-1}$ of previous layer $n-1$ have failed. This ...
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29 views

Identifying who is who - Image processing

I am working on a problem where I have to find how many people are passing through a point and how many times they pass through. A good example use case for this problem would be counting how many ...
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1answer
148 views

Homography Matrix Correlations

If the homography matrix of Image 1 to Image 2 is given, and another homography matrix for image 2 to image 3 is given, how do I calculate the homography matrix for image 1 to image 3? PS : I need the ...
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1answer
111 views

Image reconstruction using Irradiation

I am a bit confused as to how to go about this. I have a surface [x,y,z] given by: ...
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255 views

Prediction-error filter for images

I am interested in studying local pixel value dependencies in images and I am wondering if it exists a general form of prediction-error convolutional filter that is able to suppress the image's ...
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73 views

Which is faster: image segmentation or line detection?

Some papers use image segmentation techniques and others use edge detection. I need to know which one is faster. update: I need to do semantic segmentation for outdoor sense and the data is optical ...
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103 views

MATLAB: Normalize Image in Frequency Domain

I have 3 different images and I have the data which is in frequency domain. The data size is : 192x256x88x32x3. ...
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2answers
225 views

Easy way to get rid of noise in a hand drawing

I would like to take a user's hand drawn input, and filter out "noise", aka small sketches or blobs, where the user might have screwed up and accidentally touched his hand to the drawing device, or ...
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573 views

Average gradient of pixels and sum of absolute diference

Studying the research paper Multidirectional Scratch Detection and Restoration in Digitized Old Images, E. Ardizzone et al., 2011: I have several questions regarding this section (5. Restoration), ...
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62 views

Enhancing very thin lines in images

I want to detect filopodia (red arrow indicates filopodia in a vessel image). My strategy is that if $I$ is the original and $J$ is the another image after opening operation. Then, $I-J$ is the ...
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159 views

What is the Center Frequency of Gabor Filter?

If the standard form of a Gabor function is as follows, $$ g_{\lambda, \theta,\varphi, \sigma,\gamma}(x, y)=\exp\left(-\frac{x'^2+\gamma^2y'^2}{2\sigma^2}\right)\cos\left(2\pi\frac{x'}{\lambda}+\...
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255 views

circle or arc recognition in noisy image

I have an image that is missing the center and contain what seems to be two parts of circles or maybe two arcs. What is a good metric or signal processing approach to use to differentiate between the ...
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51 views

What is the difference between “tree-based clustering” and “tree-based classification”?

Clustering is an unsupervised learning method and classification is a supervised one. I understand that a tree can be used for image classification since it is based on decision tree in which we have ...
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1answer
447 views

How to use the Walsh-Hadamard transform to filter 24 bit RGB color values in a localized spatial region?

After reading this Signal processing Stack Exchange article tonight, What is the Walsh-Hadamard Transform and what is it good for?, I became interested in applying the Walsh-Hadamard transform to ...
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38 views

Counting percentage of fouling on a surface

I am completely new to image processing and python. I hope I can find some help here. I am trying out a project on detecting fouling% on a ship hull using raspberry pi. I am trying to learn how this ...
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279 views

How is the luminance vector calculated for these linear matrix transforms

In the article "Matrix Operations for Image Processing" by Paul Haeberli there is an example described using a matrix to alter the saturation of an image. In the example given the author first ...
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1answer
235 views

compression algorithm

Steganography can hide one image inside another. If we have a compression algorithm that allows us to fit the bits for two images into the size of one, can we think of a way to modify a run-length ...
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2answers
434 views

Segment highly packed nuclei with dotted high intensity signal inside each object

I collected high magnification images on cell nuclei and I need to segment them (red circle in the image). The edges of the nuclei are visible but inside each nuclear object there are bright spots of ...
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29 views

DICOM Processing

I am trying to perform analysis of DICOM ultrasound images that have vascular flow rates. I am a new user to MATLAB, and I am trying to generate a line to fit the flow curve and calculate an area ...
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52 views

How to detect malformed-ellipse-alike objects?

I need to process a stack of ultrasonic images, where there is mostly a lot of noise to see, but I need to extract specific objects that look for example like this: Here is an example from Wikipedia ...
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36 views

Evaluation of circle detectors

I have several circle detectors. I want to evaluate their performance in finding the spherical steel markers in X-ray images. The radii of the circles are distributed in a narrow range around 8 px. ...
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272 views

Head pose estimation

I am looking for an efficient head pose estimation algorithm from facial features. What I already have: I already have implemented the code for stable facial landmarks(68 landmarks on the face). I ...
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224 views

Image processing: High pass filter to remove lowest 16 frequencies

How can I remove the lowest n frequencies of an image? Are the lower frequencies around the centre of the FFT result?
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474 views

how to compute horizontal angle of a pixel from a computer vision camera

My program needs to compute the angle of a pixel from a computer vision camera that has 120 degrees field of view, and resolution of 640 pixels wide and 480 pixels high. Program receives an X,Y array ...