# 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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### 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 ...
19k views

### 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 ...
47k views

### 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 ...
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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?
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### Applying Image Filtering (Circular Convolution) in Frequency Domain

To filter an image we can: Use a 3x3, 5x5, 7x7, etc. filter, that is convolve the image and the filter in the space domain. Use a FFT on both the image and the filter, multiply them together in the ...
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### Image Processing and applicability of 2D Fourier Transform

As a newbie in the world of signal processing, I am having a hard time in appreciating image 2-D fourier transforms. I am fully able to appreciate the concept of 1-D Fourier transform. Essentially, ...
26k views

### Image Reconstruction:Phase vs. Magnitude

Figure 1.(c) shows the Test image reconstructed from MAGNITUDE spectrum only. We can say that the intensity values of LOW frequency pixels are comparatively more than HIGH frequency pixels. Figure 1.(...
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### Vein extraction from this image

I have this image: What methods should I use to extract the veins from this image. Thank you.
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### Which domain used for denoising additive and multiplicative noises

I want to know what is the difference between additive noise, multiplicative noise.. In what domain these noises are handled to remove? I am interested particularly in image dataset Does different ...
2k views

### How to Zero Pad in Order to Perform Filtering in the Fourier (Frequency) Domain?

Consider an $M\times N$ image $f$ and an $G \times K$ filter $h$. Given that convolution in the spatial domain corresponds to multiplication in the Fourier domain, then we can perform a convolution of ...
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### JPEG DCT padding

Since the JPEG DCT block used is 8x8, how does the method deal with images with dimensions that are not multiples of 8? What kind of padding does it use? How are the 8x8 blocks of the image chosen?
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### recover image by only magnitude of image fourier transform

I have a image and I want calculate fft2 of it, after it I want recover image only by magnitude of it. how can I achieve this work? ...
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### what's gaussian noise look like?

I am using Matlab function imnoise to add gaussian noise to one image. However, it seems that adjacent samples of the noise is correlated. I am using matlab code below to add noise. ...
254 views

### 2D DWT computation order

In 2D the discrete wavelet transform (DWT) of an image using lifting based 5/3 filter, if I perform a row-wise operation first then perform column-wise operation then I will get 4 sub-band LL, LH and ...
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### How to find out if a transform matrix is separable?

In image processing, when we have a series of basis images, how could we know if the transformation is separable or not? For example, I know that following bases are separable and transformation can ...
635 views

### 2D DWT Image Issue

In the literature, I see that a 2D signal can be transformed by first doing a 1D transformation on each row of the matrix followed by the same procedure on each column. It seems that $k^{th}$ level ...
287 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 ...
63k 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 ...
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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 ...
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### 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 ...
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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 ...
22k views

### 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 ...
67k 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 ...
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### 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 ...
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### Is sift a good way to extract features from an image?

I am trying to extract features from an image, but I have failed to get the points that I want to extract, and hence my image fails to match with the template. Are there any checkpoints that I have ...
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### How to extract traffic signs from a photograph?

What image analysis techniques can I use to extract the traffic signs from an image such as the one below? Edit: After Anisotropic diffusion: The background that i don't want gets cleared a little ...
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### Most common modern day Image Segmentation techniques

I was doing some reading up on image segmentation techniques and I was wondering about modern day, state-of-the-art segmentation algorithms. What current segmentation techniques that are a 'must-read'...
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### Auto Detection of Rotation Angle on Arbitrary Image with Orthogonal Features

I have a task at hand where I need to detect angle of an image like the following sample (part of microchip photograph). The image does contain orthogonal features, but they could have different size, ...
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### Wavelet Transform

I want to perform 2D haar discrete wavelet transform and inverse DWT on an image.Will you please explain 2D haar discrete wavelet transform and inverse DWT in a simple language and an algorithm using ...
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### Why images need to be padded before filtering in frequency domain

In image processing books , we are told that Images need to be padded while doing filtering in the frequency domain. Why we need that zero padding ?