All Questions
Tagged with image-processing image-processing
3,213 questions
11
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1
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Opencv calcHist and calcBackProject in plain english
i've started experimenting with c++ and opencv because of i want to learn image processing.
Now, my first exercise is to create a skin detector with calcHist and calcBackProject.
But i don't ...
- 924
11
votes
2
answers
1k
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What's the Underlying Algorithm for Detail Preserving Upsampling in Photoshop CC?
The detail-preserving upsampling algorithm in Photoshop CC is truly amazing. It can upscale any image while preserving details in almost real-time. And I truly wonder how it is implemented.
I've ...
- 211
11
votes
2
answers
3k
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Counting vechicles in an image
I have been trying to implement an algorithm for successfully counting cars in an image. I have tried implementing A Method for Vehicle Count in the Presence of
Multiple-Vehicle Occlusions in Traffic ...
- 387
11
votes
1
answer
1k
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How Can I Use MATLAB to Solve a Total Variation Denoising / Deblurring Problem?
The Total Variation Denoising Problem is given by:
$$ \arg \min_{x} \frac{1}{2} {\left\| A x - y \right\|}_{2}^{2} + \lambda \operatorname{TV} \left( x \right) $$
Where $ \operatorname{TV} \left( \...
CEB12
11
votes
2
answers
23k
views
Apply a Gabor filter to an input image
I tried to apply a Gabor filter with a specific scale (according to my values of lambda and sigma, so it is (7x7) and for 4 orientations (0, $\frac{\pi}{4}$, $\frac{\pi}{2}$ and $\frac{3\pi}{4}$) to a ...
- 111
11
votes
1
answer
356
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Recover curves from noisy collection of points
Background: I'm trying to make a system that tracks a number of bubbles in a video
I'm implementing the bubble detection in the single image case using the Circular Hough Transform. Due to occlusion, ...
- 113
10
votes
5
answers
6k
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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, ...
- 155
10
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3
answers
12k
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Why normalize the data set before applying Direct Linear Transform
Direct Linear Transform (DLT for short) is a method of homography estimation, it solves the overdetermined linear system via SVD $$Ah=b$$to find a solution $h$ under constraint $\|h\|=1$. Actually it ...
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10
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2
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12k
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Understanding SURF Features Calculation Process
So, I was reading the paper on SURF (Bay, Ess, Tuytelaars, Van Gool: Speeded-Up Robust Features (SURF)) and I can not comprehend this paragraph below:
Due to the use of box filters and integral ...
- 424
10
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3
answers
24k
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Understanding the Gabor filter function
I need to implement a script for generating features from an input image by using the Gabor filter. I have no past experience of wavelets and I'm just learning Fourier analysis (I understand the basic ...
- 265
10
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2
answers
7k
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Meaning of the Transpose of Convolution
I have an $n \times n$ asymmetric convolution kernel, $k(t_1,t_2)$. $k$ is zero everywhere except for in small regions near the corners.
I also have an $n \times n$ image, $f$.
Let $*$ denote ...
- 295
10
votes
3
answers
6k
views
Why Is Bi Quadratic Interpolation for Image Resampling / Interpolation Rarely Done?
Related question: What are the practically relevant differences between various image resampling methods?
Bilinear and bicubic interpolation for image resampling seem to be fairly common, but ...
- 203
10
votes
2
answers
9k
views
Phase Correlation - Poor Performance on Noisy/Blurred Images?
I have successfully tested 1D phase correlation algorithm to determine vertical shift between two synthetic images.
When I moved to real images, however, it is not able to detect translation at all (...
- 4,275
10
votes
2
answers
5k
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Isolate the non blurred part of foucsed image
I have an image taken by a mobile phone camera with focus on a part of it let say a face or whatever.
I want to know -approximately- where is the focused area. For example, a bounding box around the ...
- 266
10
votes
2
answers
848
views
Filtering kinda "half-toned" image for OCR processing
I have a scanned PDF material to which I want to add hidden text layer, so I could index the document. I used ghostscript black and white tiff output device (tiffg4) to extract pages as tiff images, ...
- 583
10
votes
1
answer
7k
views
Why does the separable filter reduce the cost of computing the operator?
A separable filter in image processing can be written as product of two more simple filters. Typically a 2-dimensional convolution operation is separated into 2 onedimensional filters. This reduces ...
- 265
10
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1
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375
views
decision rule for image segmentation
Let $Y$ be a measured (noisy) image $Y= X+ noise$, where $X$ is an image contains $0$(Background) and $200$(object). I need to create a decision rule that determines whether the true pixel value was $...
- 470
10
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2
answers
3k
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Phase shift and phase spectrum terms in multidimensional signal
I know about phase of a 1D signal. But when I go into higher dimensions like 2D,3D etc, it becomes headache to grasp the concept.
What are the terms phase shift and phase spectrum mean in case of ...
- 407
10
votes
2
answers
6k
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What is the Compression Algorithm used by Facebook?
I would like to know what is the Compression Algorithm used by Facebook for compressing the images? I uploaded a image of size 242 Kb and I downloaded the same image from my Facebook album. The size ...
- 1,021
10
votes
1
answer
2k
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How to remove stains from images?
I have this extremely distorted and stained image
Is it possible to remove this stain ? Could image inpainting help ?
Please help
EDIT : Another image
After applying anisotropic diffusion and ...
- 2,192
10
votes
1
answer
744
views
What is the antialiasing algorithm employed by video cards?
What is the algorithm employed by video cards when one talks about for example 8xAA?
I thought the algorithm was about looking at neighboring pixels for correction. ...
- 333
10
votes
4
answers
2k
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Noise removal in medical segmented image
Can anyone suggest methods for removing the noise (indicated inside the red square) from every where in the following image, while keeping the white lines?
- 301
10
votes
2
answers
3k
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Algorithms for detection of fingertips or nails
Can you give me some advices on what could be the best algorithm(s) to use for detection of fingertips/nails in image. First thing that crossed my mind was Viola - Jones. After rethinking I concluded ...
Srđan
10
votes
3
answers
2k
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Denoising by DCT and hard thresholding
If I have an image and I find the DCT and then apply hard thresholding on the coefficients and then IDCT then I have attenuated the noise.
Can someone please explain in detail or point me to the ...
- 101
10
votes
1
answer
326
views
Advise on detecting anatomical landmarks in a CT reconstructed volume
I'm trying to automatically detect some medical defined anatomical landmarks in a CT reconstructed volume. Medical doctors use these landmarks to measure some patient specific parameters.
I have ...
- 337
10
votes
2
answers
1k
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Examples of linear/logistic regression applications
I was wondering about super simple applications of linear or logistic regression to signal processing (image processing specifically)?
I'm a math guy that's been asked to explain some mathematical ...
10
votes
1
answer
6k
views
What is the link between the homography computed over 2 images and the homography computed over the same images upside down?
With OpenCV, I compute the homography between, say, these two images:
and
Don't worry about the strange white form on the right side, it is due to the smartphone holder I use. The homography, given ...
- 1,049
10
votes
1
answer
2k
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Could you describe the effects for varying different parameters of a canny edge detector?
Last couple of questions touched upon Canny edge detector
What are the limitations of a Canny edge detector? and
Best way of segmenting veins in leaves?
The basic outline of the algorithm is as ...
- 5,597
10
votes
2
answers
2k
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How to estimate octave and size for visual features positioned at Harris corners
I am currently working with and comparing the performance of several feature detectors provided by OpenCV as basis for visual feature matching.
I am using SIFT descriptors. I have accomplished ...
- 3,676
10
votes
2
answers
5k
views
How to implement a gradient based Hough transform
I am trying to use the Hough transform for edge detection, and would like to use gradient images as the basis.
What I have done so far, given the image I of size <...
10
votes
3
answers
13k
views
Chroma-Subsampling: How to properly calculate the data-rate
I am having a hard time understanding how to calculate the data rate when leveraging chroma-subsampling in e.g. a Y'UV image:
I have the following examples for a calculation:
Image resolution: <...
- 203
10
votes
1
answer
9k
views
Phase correlation vs. normalized cross-correlation
I asked this over at Mathematics Stack Exchange, but since this sort of lies on the border of the questions normally asked over there and the questions you see over here I'll ask it here as well. (As ...
- 101
10
votes
1
answer
442
views
How does auto focus in cameras work?
I am just wondering how does camera auto focus work. What kind of processing does it do on images in order to adjust the focus? Is there freely available code that detects the focus level of an image ...
- 117
10
votes
2
answers
2k
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Log-Polar DFT Based Scale-Invariant Image Registration
I'm trying to do image registration using phase correlation as described in the Reddy Chatterji paper. In my case, the images may be scaled and translated relative to each other.
The algorithm for ...
- 203
10
votes
2
answers
637
views
Image Processing - Counting nuclei
I am trying to create a program that can count the number of nuclei in such an image:
What I've already done is the following, step by step:
Apply an Alternating Sequential Filter (closing and ...
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10
votes
3
answers
3k
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Detecting a filled glass object
I've been sent here from this question in stackoverflow, please excuse me if the question comes too specific and it's not in the manners in here:)
The task is to find a glass with specific liquid in ...
- 202
10
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2
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424
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Deconvolution Question on Article "Deriving Intrinsic Images from Image Sequences" by Yair Weiss
there are n derivative filters: $f_i$, and denote $f_i^r$ as $f_i$'s reverse filter such that
$$f_i(x,y)=f_i^r(-x, -y)$$
$r_i, f_i$ given, to find $r$ from the equations:
$$f_i * r = r_i, (1 \leq i \...
- 101
10
votes
1
answer
562
views
What interpolation methods can I use to get the tightest fit for these curves?
I am working with MRI images of the brain that have certain areas marked by hand like and .
I am trying to come up with an interpolating function that will let me describe such curves so that I can ...
- 201
10
votes
1
answer
187
views
Data decomposition method invariant to small shift and scale?
Is there a data decomposition method similar to eigenvalue that estimates projection matrix to reduce dimensionality but does not project similar vectors too far away in euclidian distance terms from ...
- 287
9
votes
5
answers
1k
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Detecting tennis courts in aerial images? [duplicate]
Possible Duplicate:
How to find tennis courts in aerial imagery
I am trying to detect tennis courts that are present in aerial images ..
I have the following image:
I tried color image ...
- 2,192
9
votes
6
answers
8k
views
DSP programming in C/C++
I have exposure to MATLAB and have some basic exposure to signal processing and plotting in MATLAB... but I am more comfortable with C/C++ than MATLAB because I have been working in Image processing ...
9
votes
1
answer
13k
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3D Position estimation using 2D camera
I have a camera (iPhone), I have a 3D control object in the image that I know its properties very well. (My control object). There is also a secondary object in motion. The ultimate goal is to ...
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9
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2
answers
20k
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kernels to compute second order derivative of digital image
For an image $I$, its first order derivatives can be computed using several oprators, such as
$$K_{sobel} = \left[ \begin{array}{ccc} -1 &0 &1 \\ -2 &0 &2 \\ -1 &0 &1 \end{...
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9
votes
2
answers
24k
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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 ?
- 457
9
votes
1
answer
821
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How to expand on and deepen a basic skill set for image/video processing?
I didn't take any class on image processing but I studied the subject based on lecture notes and important books for last three months. So at this point, I would like to sharp my image processing ...
- 1,229
9
votes
1
answer
11k
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FFT of image data: "mirroring" to avoid boundary effects
I load and display an image of some rice in Matlab:
g = imread('rice.png');
imshow(g);
I take the FFT of this image and shift it:
...
- 1,783
9
votes
4
answers
3k
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How to do De-Houghing of a Hough transform'ed Image?
I'm working with code found at Rosetta Code for creating a Hough transform. I now want to find all the lines in an image. To do so I need the ρ and θ values of each of the peaks in the Hough space. A ...
- 743
9
votes
2
answers
3k
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Surface detection
How would one segment large area's of gray (ranging from white to black) from an image ? (If you know this in opencv, you may answer by saying what you would do in opencv). For example given this ...
- 392
9
votes
3
answers
3k
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FFT for line detection
I am trying use the FFT in a different way then most people ask about. I want to be able to take a picture of a graph with regular repeating vertical lines, and to process the image to determine how ...
justagruvn
9
votes
2
answers
684
views
Finding radius r of the overlappable sphere(s) in 3D image
My current problem:
I have an input 3D binary image (a 3D matrix that has only 0 and 1) that consists of random numbers of sphere with radius r.
We do not know how many spheres are there in the ...
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