# Tag Info

### Best way of segmenting veins in leaves?

Following on from the above excellent answer, here is how to do it in python using scikit funcitons. ...

### Best way of segmenting veins from arm?

So one good step to enhance the vein-like structures is coherence enhancing diffusion: Weickert, Joachim. "Coherence-enhancing diffusion filtering." International Journal of Computer Vision 31.2-3 (...
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### What does convolving an image with kernel [1 -2 1] do? How is it different than convolving with the derivative kernel [1 -1]?

Convolution with the [1 -1] kernel (A) is a derivative filter, which computes the finite difference approximation to the first derivative. The ...
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### Detect circles in image

1) Normalize your image to range $[0,255]$. 2) Select a threshold and threshold the image. For your image, what worked is: $\tau=[140-150]$. 3) Compute a Euclidean distance transform. 4) Apply ...
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### What does convolving an image with kernel [1 -2 1] do? How is it different than convolving with the derivative kernel [1 -1]?

Both are high pass filters. Filtering with [1 -2 1] is the same as filtering with [1 -1] twice. So the longer kernel is a steeper high pass filter and emphasize the edges more.
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### Can DFT magnitude be used to identify repeating patterns in an Image?

Yes, the DFT magnitude can reveal repetition patterns in an image. I provide an intuitive understanding for the results returned by the DFT which will hopefully make the interpretation of the DFT ...
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### Gap Filling Contours / Lines

I managed to find a solution of your problem by simply using a disk-like structuring element instead of a square/rectangular one for the closing operation. A comparison of both approaches' results is ...

### Best way of segmenting veins in leaves?

This topic has always attracted a lot of interest, and yet no real consensus exists on the topic. Therefore I decided to drop a few words. My answers to previously asked similar questions on ...
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### How we calculate Precision-Recall Curve?

You're right. When you just have a single precision and a single recall value, you get a precision-recall point, not a curve. However, machine learning models typically do not output discrete ...
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For the sake of putting some numbers to this question, I implemented a basic histogram of gradient from scikit-image (skimage.feature.hog). Here is the timing data ...
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### Finding minimum in the middle of a histogram

To me, this looks like you want something like start from right. Add up bins' values, as long as the added bin is larger than the last or the value added by that bin divided by the current sum is ...
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### Lighting for computer vision automisation

What I learned so far that my lighting is not good. It's coming from a fluorescent lamp from that's right above the camera. Apparently I would have to diffuse the light with some sort of material. The ...
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### Fitting a grid to points in a 2d space

You could represent the grid with 5 parameters: (x0, y0) to represent the offset from your image origin to the grid origin (xs, ys) to represent a multiplication factor from your image plane to your ...
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### Should Edge Detection Be Applied in Spatial or in Frequency Domain?

We need to separate the concept of edge detection from the tools we use to apply the procedure. Edges are local property of the image. Being so local means we don't analyze the image in frequency ...
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### Any good alternatives of ImageJ (Fiji)?

If you’re looking for a large collection of image processing functionality geared towards quantification, I will recommend DIPlib (I’m an author). It is different from ImageJ in that it doesn’t have a ...
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### Comparison between watershed and grabcut

Watershed-based segmentation will typically lead to over-segmentation, and is very sensitive to local image noise (e.g. see discussion here). Typically watersheds are pruned/merged by using thresholds ...
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### Scikit-Image, Numpy, and Selecting Colors (python)

Thanks to Maximilian Matthé, I have an answer. Below is his OpenCV code translated to Scikit-image. Note that I changed some parameters (e.g., reduce the size of the morphological disk) to replicate ...
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### Scikit-Image, Numpy, and Selecting Colors (python)

You can look at your picture in a different color space, e.g. the HSV space. In this space, each pixel has 3 components: hue, saturation and value. Hue defines the color's tone, saturation the color's ...
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### 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 ...
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### Simple technique to segment out optical disk and vessels from retinography

I managed to get a decent segmentation of the optical disk and vessels by applying some basic operations to the input image, starting with loading and grayscaling it: ...

### How to detect the fuzzy edge in this image?

bacteria segmentation is a broad field with many approaches. here's an example. For your spesific image, I think you can do the following tricks: ...
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### edge detection evaluation methods

I strongly agree with Ava. Without a clear formulation of your task, you cannot make a meaningful ranking of algorithms. Think about your most important task and formulate clear goals. Here is an ...
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### Calculating distance between two blobs in a binary image in microns

This is relatively straight-forward with OpenCV and numpy. Step One: Using OpenCV's Blob Detector you can do something like this: ...
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### Is deep learning the only way to detect humans in a picture?

One of the popular feature descriptors used for human detection is HOG - Histogram of Oriented Gradients. Usually you would train a classifier for recognizing human vs non-human, and then you would ...

### Double Threshold Mechanism

It is possible that it refers to hysteresis thresholding. This is where the image is thresholded twice, at a low threshold and a high one. The connected components of the low threshold that contain at ...
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### What is the application difference between extent and solidity in image processing?

I would suggest that Solidity is the better measure. Extent would be a cheap approximation. It’s cheap because computing the bounding box is cheaper than the convex hull (and really simple to ...
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### Image processing: How to find center of biggest blob in an image?

do a distance transform. you'll see why that's a good idea: for every pixel you get the shortest distance to a border. that's exactly the radius of an inscribed circle. from this, just find the pixel ...