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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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Is the Bilateral Filter a Solution of Some Variational Method?

I've been watching these video lectures about variational methods in computer vision. In one of such video lectures a it is explained for example that the Gaussian filtering is a solution of the ...
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The Gradient Operator of a Vectorized Image in Matrix Form

I have this optimization problem: $$ \arg \min_{ X \left( i, j \right) } \sum_{i, j} \left\| X \left( i, j \right) - 255 \right\|_{2}^{2} + \lambda \sum_{i, j} \left\| \nabla X \left( i, j \right) - \...
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97 views

Automatic Image Enhancement of Images of Scanned Documents (Auto Whitening)

Dropbox have make a blog post about there automatic enhancement method for scanned document image - Fast Document Rectification and Enhancement. I followed the post and they mention a formula to make ...
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1answer
68 views

How to Approximate the File Size Ratio of Two JPEG-LS Compressed Images? [closed]

For instance, a high-resolution image (25MP) and a low-resolution image (4MP) of the same scene. When compressing them both with ...
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How Can JPEG Be Used to Realize a Transfer Application with a Fixed Bit Rate? [closed]

For simplicity, assume a fixed bandwidth (5MB/s) and that each second an image with 12MP is generated. The quality of the image ...
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1answer
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Most reliably and rapidly readable 2D barcode?

QR Codes are far and away the most popular 2D barcodes for mobile applications these days. However, there are several other widely-used 2D barcode symbologies as well, including Aztec (used in the ...
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438 views

Scale invariant template matching

For my application I am looking for a free, fast and scale-invariant template matching algorithm. The templates can only be scaled within the scene (no skew or rotation) and the scale is unknown. ...
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1answer
78 views

Circle detection with incomplete edges

I want to detect circles in the image below but this approach, of using cv2.approxPolyDP on contours and counting the sides of the polygon, doesn't work here since some of the circle is missing. Is ...
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1answer
84 views

What Are Different Approaches to Realize a Gaussian Blur (Smoothing) Step on an Image? [closed]

Could some review some methods to apply Gaussian Filter (Blur) on an image besides the direct one using Truncated FIR (classic convolution with Truncated Kernel) approximation?
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Image brightness and contrast adjustment on stereo image pairs

I have a pair of stereo images captured with two different cameras. They differ in brightness and contrast as they were not captured with global shutter cameras. I need to apply semi global matching ...
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50 views

How to extract text from scene images?

I tried many methods for segmenting images like the example below ; but i obtained no efficient result can someone suggest me a good method for extracting text from complicated images like this ...
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2answers
214 views

What is a filter bank?

Suppose, I have 3 kernels: $$ \left[ \begin{array}{cc} a&b&c\\ d&e&f\\ g&h&i \end{array} \right] $$ $$ \left[ \begin{array}{cc} p&q&r\\ s&t&u\\ v&...
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Gaussian pyramid: why needs the image to be downsampled

In the context of a gaussian pyramid, why is the image downsampled separately although the numbers of pixels are decreased through smoothing already? In my understanding, the number of pixels will ...
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Robert's cross used for gradient feature extraction

I am at loss concerning the explanation of a method in the paper Detecting handwritten signatures in scanned documents by Cüceloğlu and Oğul. The aim is to identify the location of a signature in a ...
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1answer
46 views

opencv otsu binarization not working

I tried to apply opencv OTSU binarization on the following image, but it generate a black image. Here is the following python code: ...
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How do I interpret the Matrix resulting from 2D Fourier Transform of an Image? [duplicate]

I asked this question on StackOverflow but was told that it was better suited for here. I am having trouble understanding the result of the 2D Fourier transform on images. Are the indices in the ...
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1answer
345 views

Is there a penis detection demo similar to face detection?

Tutorial for face detection: Is there a script / tutorial / demo for penis detection? These guys ran into some issues: Fairly serious question, future of internet memes is at stake. Breast / ...
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2answers
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improving pre-processing (noise removal) orange seven segment display for OCR reading

About this project: Older images have the date they where taken placed on the image, in the bottom left hand corner. The goal is to extract this date and put it in the EXIF data of the scanned photo. ...
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1answer
131 views

Intuitive Meaning of Regularization in Imaging Inverse Problems

Hello Every one I have been trying to understand the intuitive meaning of using a regularizer in images. Specifically what does the Total Variation regularizer do in images and how is it able to ...
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Vector VS Raster for Image Scaling

I am working on production-grade Image Scaling based on Java. Use Case: For serving cards(credit cards) on different devices/platforms. I wanted to know which approach I should consider in software ...
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243 views

Using Ordered Dithering Given a non-monochrome palette

Good afternoon. I've been looking into image processing techniques to reduce the amount of color, and one of the ones I"ve come across is ordered dithering (Wiki). In the examples I've seen online, ...
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2answers
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Is SSIM a measure of mutual information?

As i have seen contradictory information online: is the quality measure SSIM between two images (one base-line, one distorted) directly correlated to the mutual information between the two. One one ...
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2answers
72 views

Are there any quick way to tell if a kernel is a high-pass filter?

Im new in this image processing field so please be gentle with terminology, i have a kernel of 3x3 and i want some way in order to test if its a high pass filter or not Thanks in advance
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How to flatten this OCT image with respect to the marked line

I am working on a medical image processing project where I have to use retinal OCT images. I am using the dataset available here. This dataset has a lot of images and I want to flatten all of them. I ...
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Feature Extracting from an image from JAFFE database using gabor filter

I am trying to implement a feature extractor using gabor filter in MATLAB. I have taken images from the JAFFE Database. Here is my code: ...
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1answer
54 views

How to make series circle shift invariant

I have a series of numbers. They may be integer, floating, or ...
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1answer
129 views

Subtracting DC Offset a Complex Signal?

If I take the magnitude of a complex signal, and then subtract the mean amplitude, I remove DC offset but lose the real and imaginary components. How can I properly subtract the DC offset of a complex ...
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Square grids in single-pixel cameras

I have read a few research papers where the authors used Hadamard matrices as masks for image capture. In almost all of them the arrangement of the mask is square, e.g., some use a Hadamard $4096$ to ...
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1answer
62 views

Wiener deconvolution in cpp giving back the same image

I was trying to deblur a noisy image using wiener deconvolution. I found this code which added noise to an image and removed it as well. Modifying this code only i tried to implement the exact formula ...
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1answer
40 views

How Can PCA Be Used in Image Analysis [closed]

I am still a not how PCA can be used in image analysis and where is it is mostly used. For example how can PCA be used in order to differentiate between different faces? Can you please mention other ...
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2answers
297 views

How to Classify a Kernel as Low Pass Filter (LPF) or High Pass Filter (HPF)? How to Transform an LPF Kernel into HPF Kernel?

The filter impulse response is [1/9 1/9 1/9;1/9 1/9 1/9;1/9 1/9 1/9]. how do i determine whether it is an Low pass filter or a high pass filter. If this is a low pass filter how do i convert it to a ...
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2answers
60 views

What are some current algorithm(s) for finding if two images are copies of each other?

Could anyone enlighten me on what are the current best ways to detect if two images are the same (i.e. a copy or edited copy of each other)? What feature detection method do they use (SIFT, DWT, pixel ...
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1answer
78 views

Gaussian Equivalent of Convolving an Image 50 Times with a Box Filter

I have a image that I'm convolving 50 times with a box filter, and I like to replace this with a single gaussian filter. Because both box filter and gaussian filter are separable I can just study the ...
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1answer
37 views

How does reconstruction function relate to watershed segmentation?

I'm trying to understand how watershed work by reading The Morphological Approach to Segmentation: The Watershed Transformation S. Beucher and F. Meyer This document mentions the reconstruction ...
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1answer
662 views

Use of the Sobel Filter for Image Gradient [MATLAB]

I am using the Sobel filter for an RGB image. I have found two different ways to do that and the results look a little different. What is the difference between these two methods? Method 1 ...
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1answer
978 views

Convolution and cross-correlation on 2D image (Example)

I have read that convolution and cross-correlation are the same thing, but convolution flips 180 degrees (images), or time reverses (sequences) the kernel, before performing the elementwise ...
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Fast Calculation of Legendre moments in images using kernel-separability

I am implementing zero order approximation method to calculate Legendre moment of an image. One simple way to calculate moments is directly using loops and calculate the double summation as given in ...
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1answer
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Best way to fill an image placed into a larger box without creating artificial edges?

If you are training a neural net for a bunch of images of different size, and you have to put them all in a same-size enclosing box for input to the neural net, what's the best way to fill the ...
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Estimating the deformation of a printed label in an image

For a university honours project, I am developing an algorithm to read the text on nutrition labels. One difficulty I have encountered is how to 'flatten' the text in images of labels that are very ...
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88 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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364 views

Understanding scipy.ndimage.filters.convolve function

So I am using scipy.ndimage.filters.convolve function. I understood how it works for 2D matrices from the documentation. But when I apply this to 3D matrices it is ...
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1answer
190 views

SSIM(YUV) vs SSIM(Y): values very different

I'm seeing some weird results when trying to compare image qualities in a few different color spaces. Have a look at my graph: I want to compare with another publication, which reported PSNR(YUV) and ...
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2answers
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Image processing: How to find center of biggest blob in an image?

Let's say I have an image like this one, and have masked it so all yellow pixels are 1 and all black pixels are 0. I would like to (1) fit the largest possible circles containing solely yellow pixels ...
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2answers
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Is there a way to measure each pixel's content in an image somehow?

Is there a way to measure each pixel's content in an image somehow? Like can I interpret each color as some kind of a single value, rather than a triplet? Perhaps I can think of them as $\mathbb{R}^...
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1answer
187 views

How to detach overlapping contours but not to remove small ones. Alternative to erosion-dilation cycle

Background: I'm trying to detect trees on a sequence of aerial images by calculating a stereo disparity for consequent pairs of images. This is how disparity looks like. White spots are trees: Next, ...
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1answer
39 views

How to recognize for small video sequence with a large sequence?

I'm working on the idea of recognizing a small video sequence (a sequence of 18 seconds) within a long one (a sequence of 15 minutes), the first idea that come to mind stats that I have to ...
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1answer
71 views

Image Histogram - What Is the Interpretation of PDF

For digital images (assume 2D gray scale image), the normalised intensity histogram is often treated as the probability distribution function of the intensity ie., intensity is treated as a random ...
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1answer
200 views

How do steerable pyramids work?

I'm reading a paper about texture synthesis using pyramids, and the very first section mention two methods for constructing pyramids, one is the Laplacian Pyramid (which I'm quite familiar with), the ...
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Given the 4 corners of two QR codes on a photographed sheet of paper, can we get a deskewed rectangular image?

I made a photo of 2 sheets of paper with a phone camera, each of them cropped at the: (x1, y1) top left corner of top QR code (x2, y2) bottom right corner of bottom QR code I hoped that the x, y ...
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Linear Predictive Coding in Gray Scale Image

I was trying make linear predictive code in gray scale image and want to find first 5 correlation values where the grayscale pixels are: [$S_2$][$S_3$][$S_4$] [$S_1$][$S_0$][$blank$] And i want to ...