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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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Calculate image brightness with python

for a project. How to code by inputting an image in python and calculate the image brightness?
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How to calculate the variance of noise when an image is downsampled?

I have a noisy image for which I know the noise variance. (Basically I created noisy image by adding noise). Now, I'm downsampling this noisy image. How does the noise variance change? Is it possible ...
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What metric can I use to give results from a computer vision application?

My application uses different light sources to visualize some patterns but these can only be observed on backlight. Some of these sources are the sun at noon, sun at dawn, at dusk, etc., incandescent ...
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How does phase relate to motions in an image?

There is lots of research based on exaggerating motions by decomposing an image into complex sub-bands using pyramid representations such as the complex steerable pyramid and manipulating phase ...
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12 views

fitting lines based on image content with python

I trained an algorithm for road semantic segmentation that gives an output like this: I want to retrieve the coordinates of the vanishing point (the top of the triangle) and to fit two lines ...
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Switching camera angle based on several images

Given a number (3 or 4) of different images of a given subject from different angles, how do I interpolate to an angle that isn't available on any of the photos? What is this technique called and is ...
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34 views

Method(s) to extract text from different sections of a invoice [on hold]

Since the content of this picture is in Chinese, you do not have to try your methods on this image. A similar image with English content suffice.
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problem in selecting correct algorithm for project (RCNN)

I am doing a deep learning project in which i have to identify different models of cars. i am a bit confused for the following reason: first is what algorithm should I use. I have studied that RCNNs ...
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Calculating the Mean Square Error (MSE) in Wavelet Denoising

I´m currently reading the paper (to be more precise: it´s a chapter from the book "Shearlets, Multiscale Analysis of Multivariate Data" by Kutyniok and Labate) "Image Processing Using Shearlets" by G....
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Is there a way to find a picture inside another picture, using only 2D Fourier Transforms of both images?

Can Fourier Transforms of both images tell anything about "likeliness" of two pictures? If yes, how precise? Can it still work if only several pixels are different or can it tell they are same if one ...
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1answer
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Confusion regarding lacunarity of koch curves with same fractal dimension but different orders

I'm trying to use the concept of lacunarity to classify images, as per how a few research papers have done it. To verify whether my equations and implementation are correct, I'm trying to verify the ...
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1answer
31 views

Scratch Detection On Noisy Textured Surface

I wish to extract long thin scratches from the noisy background image.I have tried several ways such as stacking smoothed image with input image to remove some of the noisy background patch before ...
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retrieving complete 2d autocorrelation function from 2d power spectral density function (numpy.fft.ifft2)

My question is at the boundary between signal processing and python. I have a 2d power spectral density function (PSDF) constructed on Nx/2 + 1 and ...
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1answer
38 views

Why does White Noise in images imply noise in adjacent pixels are independent?

My professor said in the class that for "Additive White noise, the noise in pixels adjacent to each other are independent". How? This is what I have got so far: White noise implies that PSD (Power ...
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2answers
39 views

Correlation between 2 signals of uneven dimensions

As a part of my work, I am trying to correlate the audio signal in a video with the pixels of each frame. The steps I follow are: Audio sampling rate and frame rate of the video are known. So, ...
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What are the differences between Gaussian down-sampling and bicubic down-sampling in Matlab? Which is more accurate for simulating low resolution?

I see in some of the technical papers, good practice for downsampling is to first pass the image through a Gaussian Filter and then take sampling to avoid problems like aliasing and so on. However, ...
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Can anybody explain the difference between SIFT and GLOH image descriptors

There are very few resources on GLOH (Gradient Location and Orientation Histogram), Can anyone explain how is it different from SIFT?
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1answer
36 views

Why is the size of results from FFT half the size of the input, while that is not the case in image processing?

When dealing with real data, Fourier Transform produces symmetric results and FFT algorithms discards half of it. An input with 1024 points will yield only 513 points in the output. However, in image ...
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1answer
22 views

Error due to downsampling an image

I have two images $I_1$ and $I_2$ suppose $I_2 = downscale(I_1)$, so for example if $I_1$ has resolution 1024x1024 $I_2$ could be 512x512. How can I measure how much quality I've lost during this ...
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2answers
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Is the Sobel filter a high pass filter, and if not, what is the difference between them?

I am an artist with an interest in signal processing. I realize that maybe this question very basic, but the web banner on the frontpage says "anyone can ask", so I assume that means beginners too. ...
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14 views

Bundle adjustment optimization parameters

While reading the Wikipedia article on Bundle adjustment, I came across the following objective function used to represent the bundle adjustment problem. I have two questions regarding this objective ...
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0answers
15 views

Amount of pixel eroded

Is there a definite relation between the kernel size and shape of a morphology change and the amount of pixels added or removed? I have a case where I have a segmented image, and I need to remove x ...
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0answers
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Filter imaging based on the spectrum image

On the left I have the noised spectrum image can we choose which filter to work based on it? For example in the 3rd row it seems that all the energy is concentrated in the middle so we need to "...
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23 views

Detection of Video Quality Using Python

I am getting started with image/video processing. As a start I have a dataset for which the goal is to detect the quality as the video progresses. Based on my readings I think any video under test ...
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Polyphase FIR image downscaling

I recently started designing a Polyphase FIR filter in with a lanczos kernel interpolator to resample an image in Python. The goal is to downscale the image using these methods. However, I think I don'...
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Corresponding filter in the frequency domain

If we take a 7 by 7 mean filter in the spatial domain, the corresponding filter in the frequency domain is the sinc function? Is there is a list of filter in spatial domain and corresponding function ...
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Adaptive Clip Limit on CLAHE

I am working on CLAHE algorithm in order to contrast enhancement. I try to find best clip value to get best result image. However, each input image desires different clip value. Therefore, I need an ...
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0answers
22 views

Which frequency filter is it?

To which frequency filter the following operator is equivalent? -1 0 -1 0 4 0 -1 0 -1 In the image domain, it is a laplacian rotated by 45 degrees. In the ...
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22 views

Rotation invariant vs rotation variant

I have a very basic question. We have Rotation invariant filters and filters which are not invariant to rotation. Now let us suppose I want to apply one of these filters. How can I decide which one is ...
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1answer
23 views

What principles to use, in order to create field that will be read by OCR?

I currently have an invoice, where some numbers are written by hand, and I would need to read them automatically. My past experience is that people who write numbers will them write in so many ...
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0answers
31 views

How to normalise data for iterative computation of extrinsic camera matrix?

Hartley & Zisserman defend that data normalisation is an essential step prior to the estimation of geometric image transformations. The reasoning behind this, as stated in their book [1, Section 4....
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1answer
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How should I go about cleaning up this kind of images? (algos)

I want to extract text from some images with messy backgrounds. First step was switching to gray scale, applying an edge detection algorithm, and then cleaning up a little bit. Here's an example of ...
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1answer
45 views

Determining parameters of S-function

I know that S-function (membership function from fuzzy set theory) is a commonly used function for image enhancement. I am reading a paper titled 'A Novel Fuzzy Image Enhancement using S-Shaped ...
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34 views

Performing inverse DFT after taking conjugate of the result of DFT

The following is a question I got in my school assignment. Pick an image and follow the operations Multiply image by (−1)x+y. Compute the DFT. Take the complex conjugate of the ...
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1answer
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Performing DFT twice on an image. Why am I getting an inverted image? [duplicate]

I was asked to perform DFT on an image twice as a part of my school assignment. Why am I getting a blurry inverted image when I perform DFT on an image twice? Sorry, I'm new to image processing and ...
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52 views

How to set sigmas and kernels for 3D-Laplacian of Gaussian filters to blob detection in Matlab?

I have written code according to a paper for Lung CT images, but its output wasn't correct. I think it is because of the setting of its parameters. The paper is about a multi-scale method using a ...
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1answer
269 views

What is different between Euclidean distance and the Geodesic distance?

We have two kinds of distance in image: Euclidean distance and the Geodesic distance. What is different between them? Could you show mathematic formula or visualization to make it clear? The reference ...
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Which algorithms can efficiently identify rectangular regions in noisy greyscale image?

I have a large number (~50000) of square greyscale images, about 180x180 pixels. I need to efficiently scan them for containing significant block like regions. See the following pictures where I have ...
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27 views

Multifractal analysis of an image using wavelets

I want to measure the fractal character of images using a wavelet approach (if possible) in python. (E.g., maybe things like roughness, anisotropy, or just the fractal dimension - perhaps just ...
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python: how to compute the color distribution of image in the paper with python and openCV

I am computing the color distribution of image as mentioned in the paper: https://arxiv.org/pdf/1202.2158.pdf. ...
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4answers
101 views

Detecting moved and dirty areas between two snapshots/images

I'm new to image processing and trying to figure out best way to identify 'moved' and 'dirty' rectangles between two desktop screenshots.Basically, lets say there is a round circle moving on a screen, ...
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1answer
21 views

Can Normalized Cut be used to find connected components in binary images?

I'm unsure whether Normalized Cut can or can't be used to find connected components in binary images. I would argue that it could, but could not validate this argument.
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1answer
59 views

python: how to compute the sharpness features of image

I am extracting the sharpness features of image as shown in the following image mentioned in a paper. I have done with the following code. Firstly, use the open cv convert the RGB to HSL (luminance ...
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0answers
15 views

MatLab-Finding error in hough line transform

Can I calculate the number of error in Hough Line Transform using MatLab? I did Hough Line Transform process from Canny Edge Detection, but it is unable to detect all the lines. Thanks.
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1answer
61 views

Chroma key algorithm with unknown background color

Suppose that I have an image with a foreground subject and a monochrome background. The image is a real world picture so the pixels belonging to the background do not share the same exact value. I ...
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1answer
32 views

python: how to compute the gray level histogram features as mentioned in the paper, and

Hi I am extracting the grey level features of image mentioned in this paper (part 4.5 low level features). "We describe two low level features that are particu- larly important for photo quality ...
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0answers
33 views

How do piecewise affine transformation work?

How can piecewise affine transform be used to warp an arbitrary collection of input landmark coordinates to a corresponding set of base coordinates? Can anyone give any physical examples, the book I ...
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0answers
32 views

On Human (Face) Detection

There are many face detection and recognition algorithms and APIs out there; however, most of them can produce same results for paintings and avatars as for human face. So, is there any specific ...
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0answers
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Amplifying the difference of luminance between pixels of color images?

I'm doing some research on digital watermarking and came across an article that embeds QR codes on mostly grayscale images and the extraction part for color images is quite confusing the article ...
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1answer
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Zoom an image with respect to a given image

I posted this question in stack overflow, but I think it is more appropriate here: I have a reference image - 'image_01.png' of size 200x200 and resolution 72 px/in. I have another image 'image_02....