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# Tag Info

### 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. ...
Accepted

### What's Logic Behind the Construction of Sobel's Filter in Image Processing?

A first rationale is to be very short, as there was a time when computing on images was expensive. Then, a contour or an edge often present a fast variation in image intensities, that can be enhanced ...
• 31.9k

### detect to rising, stable and falling point in non-smooth rectangular wave

The usual approach to change detection is the CUSUM algorithm. I've done an implementation that just addresses the level (mean) change issue. It's included (in R) below. The black line is the noise-...
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### Is the Sobel filter a high pass filter, and if not, what is the difference between them?

They are both highpass type filters, but used with very different intentions. One should immediately observe the fundamental difference that the output of unsharp masking filter is an enhanced image ...
• 28.3k
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### Separating dominoes pieces from one another and counting them

I successfully solved the problem. for those who are curious: I used histogram equalization to improve shaded edges used a slight gaussian blur and applied thresholding to remove most of the noise ...
Accepted

### Are 2nd Order Edge Detectors More Susceptible to Noise?

Suppose that the noise is a random vector $X$ with normal zero-mean components of variance $\sigma_i$, mutually independent, then for the linear combination (the $g_i$ being for instance coefficients ...
• 31.9k

### why do directional derivatives work better with a gaussian filter?

Well, look at your original picture: it's constant for all points but the edges, which means your derivative is zero for all points but these edges. By applying a "rounding, smoothing" filter to it, ...
• 31.1k
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### Intuition behind image derivative using Fourier Transform for edges detection

In general, the time derivative property of the Fourier Transform is given as $$\mathscr{F}[\frac{d}{dt}x(t)] = j\omega X(j\omega)$$ Notice that we can simply multiply by the frequency index in the ...
• 52.1k
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• 31.9k

### Detect almost circular shapes in RGB image

The image itself is somehow blurred a little. Whole edges of trees are not visible. The only clue of tree existence seems like shadows. So I suggest using shadow information and watershed transform ...
• 264

### How to apply Prewitt Edge Detection algorithm on a given image?

I was able to answer my question after doing more research. The key is to slide the 3x3 kernel and perform Gx and Gy (gradient for the x and y directions) and calculate the output image values. For ...
Accepted

### edge detection evaluation medical test images MATLAB

The closest resource I have come across is the BSD500 database: http://www.eecs.berkeley.edu/Research/Projects/CS/vision/grouping/resources.html It is a set of natural images that have had the ...
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