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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174
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5answers
61k views

“River” detection in text

Over on the TeX stackexchange, we have been discussing how to detect "rivers" in paragraphs in this question. In this context, rivers are bands of white space that result from accidental alignment ...
109
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6answers
59k views

What does frequency domain denote in case of images?

I was just learning about the frequency domain in images. I can understand the frequency spectrum in case of waves. It denotes what frequencies are present in a wave. If we draw the frequency ...
64
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4answers
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What are some free alternatives to SIFT/ SURF that can be used in commercial applications?

As far as I understand, both SURF and SIFT are patent protected. Are there any alternative methods that can be used in a commercial application freely? For more info on the patent check out: http://...
63
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8answers
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Why do we use the HSV colour space so often in vision and image processing?

I see the HSV colour space used all over the place: for tracking, human detection, etc... I'm wondering, why? What is it about this colour space that makes it better than using RGB?
54
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8answers
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What are some good signal and image processing blogs worth following?

Are there some good sites or blogs where I can keep myself updated on the latest news and papers about image and signal processing research, or I should just check out "classical" providers like IEEE ...
52
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10answers
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Is deep learning killing image processing/computer vision?

I'm looking forward to enroll in an MSc in Signal and Image processing, or maybe Computer Vision (I have not decided yet), and this question emerged. My concern is, since deep learning doesn't need ...
47
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6answers
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Best way of segmenting veins in leaves?

I have done a lot of research and found out methods like adaptive thresholding , watershed etc that can be used of detecting veins in leaves . However thresholding isn't good as it introduces a lot of ...
47
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4answers
21k views

Analogous Library to OpenCV for Audio Processing / Analysis

I understand OpenCV is the de facto library for programming image processing in C/C++; I'm wondering if there is a C or C++ library like that for audio processing. I basically want to filter raw waves ...
45
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3answers
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What algorithm does Google use for its “Search By Image” site?

What is your best guess how Google Image Search works? I can upload a photo and can search for similar images. What algorithm does it use to identify similar images?
45
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5answers
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Point Pattern Recognition

Having two different size of sets of points (2D for simplicity) dispersed within two different size squares the question are that: 1- how to find any occurrence of the the small one through the ...
40
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1answer
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How to flatten the image of a label on a food jar?

I'd like to take pictures of labels on a jar of food, and be able to transform them so the label is flat, with the right and left side resized to be even with the center of the image. Ideally, I'd ...
39
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6answers
5k views

What Properties Make Certain Wavelets “Better” Than Others In Image Compression?

I am trying to teach myself more about image compression using the wavelet transform method. My question is: What is it about certain wavelets that make them preferable when compressing images? Are ...
37
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3answers
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What are the most common algorithms for adaptive thresholding?

Adaptive thresholding has been discussed in a few questions earlier: Adaptive Thresholding for liver segmentation using Matlab What are the best algorithms for document image thresholding in this ...
33
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7answers
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Finding squares in Image

I need to find the squares in an image using OpenCV (no problem in matlab or any other, generally what i expect are some ideas). Consider the test image below : I need to find those coloured squares ...
32
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2answers
15k views

What's the difference between the Hough and Radon transforms?

I'm familiar with the Radon transform from learning about CT scans, but not the Hough transform. Wikipedia says The (r,θ) plane is sometimes referred to as Hough space for the set of straight ...
31
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5answers
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What Factors Should I Consider in Choosing an Edge Detection Algorithm?

I've learned about a number of edge detection algorithms, including algorithms like Sobel, Laplacian, and Canny methods. It seems to me the most popular edge detector is a Canny edge detector, but is ...
30
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5answers
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What are the best algorithms for document image thresholding in this example?

I'm trying to implement various binarization algorithms to the image shown: Here's the code: clc; clear; x=imread('n2.jpg'); %load original image % Now ...
29
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5answers
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Detecting Trail in Forest Images

Is anyone aware of any research/papers/software for identifying a trail (as a line or point-to-point curve) in an image of a forest scene (from the perspective of the camera standing somewhere along ...
28
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5answers
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Why are Gaussian filters used as low pass filters in image processing?

In 1d signal processing, many types of low pass filters are used. Gaussian filters are almost never used, though. Why are they so popular in image processing applications? Are these filters a result ...
27
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5answers
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Good language for computer vision?

I am trying to implement a content based image retrieval system but before I do so I would like to get an overview of some programming languages suitable for this task (having good libs and such). ...
25
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4answers
2k views

Find the stomata in a plant microscopy image

Here is a question for image processing experts. I am working on a difficult computer vision problem. The task is to count the stomata (marked below) in DIC microscopy images. These images are ...
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3answers
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How can I reconstruct a 3D structure from a set of images?

I have a set of contours (set of line segments) grouped in the following way: $S_i = \{I^0, I^\frac{\pi}{4}, I^\frac{2\pi}{4}, \ldots, I^\frac{7\pi}{4} \}$ where $S_i$ denote sequence of photos of ...
23
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1answer
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Mathematics of Harris corner point detection

This is the mathematical expression for Harris corner detection: But I have the following doubts: What is the physical significance of $u$ and $v$? Many references say it is the magnitude by which ...
22
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3answers
13k views

How do I remove motion blur?

Is there a generically accepted method of removing motion blur from an image. For a simple case, we can assume that motion happens in a straight line. I assume that it's a two part process composed of ...
22
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1answer
6k views

What are the practically relevant differences between various image resampling methods?

Mathematica's ImageResize function supports many resampling methods. Not being familiar with this area, beyond nearest neighbour, bilinear, biquadratic and bicubic ...
21
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5answers
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What are the audio equivalents of images like “Lena”, “Mandrill”, and “Cameraman”?

I don't know what to call these images, but they're very often used in the image processing world as standard examples to show the output of a particular operation. Here's a link to the page ...
20
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3answers
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Fastest Algorithm for Distance Transform

I am looking for the fastest available algorithm for distance transform. According to this site http://homepages.inf.ed.ac.uk/rbf/HIPR2/distance.htm, it describes: The distance transform can be ...
19
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4answers
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How do I detect distinct objects when their edges touch each other?

I need to find all the contours in an image retrieved from the camera. So I first use the canny edge detector to find the edges and then find the contours. Pretty simple. However, my contours get "...
18
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6answers
21k views

What is the Walsh-Hadamard Transform and what is it good for?

I am trying to teach myself about the WHT but there dont seem to be many good explanations of it online anywhere. I think I have figured out how to calculate the WHT, but I am really trying to ...
18
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3answers
9k views

What's wrong with this code for tomographic reconstruction by the Fourier method?

I've been playing around with tomographic reconstruction algorithms recently. I already have nice working implementations of FBP, ART, a SIRT/SART-like iterative scheme and even using straight linear ...
17
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4answers
11k views

What Are the Limitations of a Canny Edge Detector?

Broadly a majority of the literature on edge detection algorithms and applications that uses edge detection, references Canny's edge detector. So much so that it looks like almost "the solution" to ...
17
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5answers
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How to remove the glare and brightness in an image (Image preprocessing)?

I have an image Is there any way of removing the bright white spots ? Please help thanks Edit: After operating with gaussian and then displaying using imagesc get the following output which ...
17
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5answers
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How can I compare two pictures from the camera and tell if there are enough differences to detect movement?

I want to use my phone as a CCTV system to control a room in my house, and display an alert when something is moving. For now, what I have succeeded in doing is to grab a picture every minute and ...
17
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3answers
7k views

How to Detect Gradients and Edges in Images?

I want to be able to find points in images that are the centre of a radial gradient like the one shown in the left picture below. Any ideas on how I could use a Hough transform or some other computer ...
16
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1answer
36k views

Difference between correlation and convolution on an image?

Could you please clearly explain what is the difference between correlation and convolution that is done by a filter on an image? I mean in terms of signal processing definition I know that ...
16
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2answers
19k views

Why do we use keypoint descriptors?

I just studied about SURF and I'm going for its implementation, but I still didn't understand why we use descriptors. I understand what keypoints are and their purpose, but when we extract the ...
16
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2answers
848 views

How do you measure “detail” of a signal?

I have an image and I would like to measure the amount of detail in it. Another way to look at it is to measure how blurry an image is. One way is to analyse the high frequency components in the ...
16
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2answers
17k views

Downsampling an image by an integer factor

When downsampling an image by an integer factor $n$, the obvious method is to set the pixels of the output image to the average of the corresponding $n \times n$ blocks in the input image. I remember ...
16
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2answers
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Wiener Filter for Image Noise Reduction (Image Denoising)

I'm trying to get my head round the operation of the Wiener filter for the purpose of image noise reduction. In my case I'll have used another noise reduction filter first and will then use the result ...
16
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3answers
25k views

Difference between SNR and PSNR

I understood that SNR is the ratio of signal power to the noise power. In terms of images, how the original image is affected by the added noise. In PSNR, we take the square of the peak value in the ...
16
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2answers
32k views

Are there any good open-source (well, free) handwriting OCR programs?

The title asks it all. I have before me a data entry task that I'm not too enthusiastic about: 50-100 pages of handwritten sign out/sign in logs. The format of the logs may help. Pages are ...
16
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1answer
3k views

Removing Glare from Image

Disclaimer: I am in NO way engaged in signal processing. Just very curious... Ny question is, very simply: is it possible to apply software processing to an image to remove or reduce headlight glare?...
15
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4answers
4k views

List of possible image features for content based image retrieval

I am trying to find a list of possible image features like color, oriented edges and so on for measuring their usability in case of finding same/similar objects in images. Does anyone know such a list ...
15
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7answers
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DSP or signal/image/data processing jokes

Some other StackExchange/StackOverflow sites are entertained with a certain level of humor or fun. What is your favorite “data analysis” cartoon? is particularly worth mentioning (IMHO) this xkcd ...
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5answers
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what is smoothing in very basic terms

What is smoothing and how can I do it? I have an array in Matlab which is the magnitude spectrum of a speech signal (the magnitude of 128 points of FFT). How do I smooth this using a moving average? ...
15
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3answers
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Can Gabor filter be used for detecting dents in cars?

I am doing some research on Gabor filters for detecting dents in cars. I know Gabor filters have had widespread use for pattern recognition, fingerprint recognition, etc. I have an image. Using some ...
15
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4answers
17k views

How can I remove shadows from an image?

I have this image I would like to remove the shadow from the image. I know a lot of different methods like certain morphological operations have been used to remove shadows: I have created this ...
15
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3answers
46k views

Gaussian Blur - Standard Deviation, Radius and Kernel Size

I've implemented a gaussian blur fragment shader in GLSL. I understand the main concepts behind all of it: convolution, separation of x and y using linearity, multiple passes to increase radius... I ...
15
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2answers
19k views

Find circle in noisy data

I have an image that looks like the one below: I'm trying to find the radius (or diameter) of the circle. I have tried using circular Hough transform (via matlab's ...
15
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4answers
6k views

People detection from above

I am trying to find some method to detect people using only one camera 3 meters above the ground. This is a frame returned by camera: UPDATE: Video test -> http://dl.dropbox.com/u/5576334/...