# Tag Info

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### What Is the Difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat Wavelet?

Laplace of Gaussian The Laplace of Gaussian (LoG) of image $f$ can be written as $$\nabla^2 (f * g) = f * \nabla^2 g$$ with $g$ the Gaussian kernel and $*$ the convolution. That is, the Laplace ...

### How do I get the most accurate camera calibration?

I decided to post this answer here because a while back, this came up as the top result in Google and its suggestions helped me. So I decided to share my experience too. Having spent countless hours ...

### In opecv function Hough circles how does parameter 1 and 2 affect circle detection and how can I adjust them to increase accuracy?

Intuition for parameters of HoughCircles: image: 8-bit, single channel image. If working with a color image, convert to grayscale first. method: Defines the method to detect circles in images. ...
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### How to remove the noise without destroying the main edge?

Use bilateral filter or anisotropic diffusion first. The effect of anisotropic diffusion is as the following: . The MATLAB code can be found here. Here is its effect on your image: Finally, non-...

### How do I get the most accurate camera calibration?

Here is a list of 'best practices' for camera calibration which I originally posted here: https://calib.io/blogs/knowledge-base/calibration-best-practices Choose the right size calibration target. ...
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### Isolate the non blurred part of foucsed image

In general, this is an image segmentation problem (http://en.wikipedia.org/wiki/Image_segmentation) into which you would be trying to isolate the focused to the non-focused regions of the image. ...
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### How to Get Rid of Ripples from a Gradient Image of a Smoothed Image?

I think it happens due to 2 things: Quantization You are working using UINT8 Image, try convert it into floating Point Image. You may do this by ...

### How to Create Image Editing Filters

The word "Filter" in Image Processing word relates to "Neighborhood" based operation on pixels. Filters in the context of Instagram and other Image Processing applications are combination of point ...
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### Is it possible to hack camera calibration without having access to the camera?

If I understand correctly, you don't need the intrinsics or extrinsics to achieve that, if a top-down view is all you want. You could basically define 4 points on your parallel lines and then warp the ...
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### In opecv function Hough circles how does parameter 1 and 2 affect circle detection and how can I adjust them to increase accuracy?

If you have an idea what size circles you are looking for, then it would be best to set min_radius and max_radius accordingly. Otherwise, it will return anything circular of any size. Parameters 1 ...
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### K-means for 2D point clustering in python

It can be done very easily with the scikit-learn. Examples are easy to find on their website, i.e. here. In my opinion it is the best way to go. Modified code example from the above link: ...
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### Python - Normalized cross-correlation to measure similarites in 2 images

I guess you can compute for each pixel the correlation coefficient between patches centered on this pixel in the two images of interest. Here is an example where I downloaded the figure attached here ...
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### Given a set of lines, find only those who are parallel (perspective)

Parallel lines in the image do intersect at a vanishing point. Therefore simply hypothesizing lines (a gradient direction at a point suffices to describe it) and voting (see Hough voting) would ...
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### Gaussian Equivalent of Convolving an Image 50 Times with a Box Filter

What you should do is work with the Variance. The Variance of Discrete Random Variables with support of $\left[ -l, l \right]$ is given by (Notice that since the Expected Value is $0$, the ...
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### How Could One Imitate Photoshop's Vibrance Filter with OpenCV?

The Vibrance in Photoshop is a mask guided saturation. What does it mean? It means we add saturation only to pixels marked by the mask while leaving others untouched. The mask evaluates the original ...

### Is it possible to convert from 2D to 3D form?

[EDITED] Here's how it's done. Steps: 1. Isolate the Road Divider Part. Then, using Houghlines, find out the longest lines in Image. Find out the extrema points that cross image boundary. You got ...
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### Feature Detection on a Circular Metal Surface for Character Recognition

Do not struggle forming a database of images to match via descriptors. This would be too computationally cumbersome and would require immerse amount of training. Such a scalable solution doesn't exist ...

### Isolate the non blurred part of foucsed image

Here is an easier approach, that does not involve sliding-window analysis. Convert your image to grayscale (this is not required, but I will assume that you only have one channel for the sake of ...

### Noise Removal from an Image Using OpenCV (Comparison to Neat Image)

NeatImage probably uses Wavelets based Noise Reduction. You can look for methods based on that. Today you need methods which are "Edge Aware", namely they smooth yet keep edges in tact. Have ...
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### What Is the Cause for Poor Results with Adaptive Thresholding?

Some guidelines for using Thresholding: Stretch the image to use the whole Dynamic Range (DR). Apply some Denoising (Very very gentle). Median with small radius would be a good idea. Unless you hand ...

### What Is the Best Color Space to Work with for Hand Detection: RGB, HSV, or YCrCb?

Intuitively, HSV is the place to easily define Skin Color Hues. Yet there is a broad work on that and even articles about the optimal Color Space for Skin Detection. Yet, you should have a look at ...

### Image Gradient: Light to Dark, Dark to Light

The UINT8 type is limited to integer numbers on the range [0, 1, 2, ..., 255]. Hence negative values are clipped into 0. A solution could be wither use other types (Floating Points) or scale and ...

### What Is the Difference between Difference of Gaussian, Laplace of Gaussian, and Mexican Hat Wavelet?

The Ricker wavelet, the (isotropic) Marr wavelet, the Mexican hat or the Laplacian of Gaussians belong to be the same concept: continuous admissible wavelets (satisfying certain conditions). ...
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### Redistributing Color in a RGB Image According to a Gaussian Distribution

After you equalize the histogram you can think of your data as a stream of variables ${X}_{i}$ where $X \sim U \left[ 0, 1 \right]$. Now all you need is to transform samples of Uniform Random ...

### Recommended Order of Performing Denoising, Deblurring and Super Resolution on an Image

If your image is modeled as an image which is noisy, blurry and heavily decimated the optimal thing to do is estimate the image given that model. The model is well defined in @Laurent Duval's ...
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### How to Remove Double Lines Detected Along the Edges by Edge Detector?

I ran the following code: ...
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### MATLAB rand and C++ rand()

It is a programming question, not a signal processing question - keep that in mind, and next time use the StackOverflow. MATLAB rand function returns uniformly distributed variable on interval $[0,1]$...

### Calculating a homography based on detected lines

I will explain two approaches for this: 1) One approach would require a line matching algorithm. After matching the lines, you could simply use the end points of the lines in order to compute ...