6
votes
How to separate text from the paper on a black and white page?
I believe the best approach here is to use a threshold based on the local average brightness of the image. Setting the threshold to be 90% of the mean value of the 11x11 grid surrounding each pixel ...
- 4,581
5
votes
discrete definitions of curl $\nabla \times F$?
Continuous
It looks like you only need 2d curl, so let's start with a simpler continuous definition:
$$ \omega = \nabla \times \mathbf{u} = \frac{\delta v}{\delta x} - \frac{\delta u}{\delta y}
$$
...
- 364
5
votes
Accepted
Iterative camera calibration - No convergence
I have to tell you.
I implemented this algorithm (even double checked with other experienced people), however no luck. I guess, this worked for the authors, but with our data there was really no ...
- 2,219
4
votes
Accepted
Which image filter acts like "surface tension"?
Morphological Closing.
A morphological closing is a combination of dilation followed by erosion; typical image processing operations available in most image processing libraries.
SciPy has a "...
- 207
4
votes
Shape measure for C-shaped objects
How about something like radial integral channel features?
Affordable person detection in omnidirectional cameras using radial integral channel features, Barış Evrim Demiröz, Albert Ali Salah, Yalin ...
- 2,219
4
votes
Eigenvalue decomposition for a very huge matrix of medical images (such as the pixel physical coordinates of CT images)
Take a look at the literature that does similar things for facial recognition -- search for the term "eigenface", for example.
The point to make in this context is that the information you ...
- 54.1k
3
votes
Accepted
Compute point-spread-function between original and blurred image
We construct an operator based on the assumption that the system is a linear space invariant system. The blurred image is denoted $b$ and the input is denoted $x$.
Since the convolution is commutative,...
- 725
3
votes
Calculate the area and perimeter of a hand-drawn shape
Writing my comment idea in more detail: Lets say you have your image input to your application as a black and white pixel array, for example something like:
Then each black pixel can be represented ...
- 1,879
3
votes
Accepted
Evaluate 3D Shape Descriptor
3D local feature descriptors for shapes are very well studied. Typically, people tend to represent the input as a set of points (point clouds) and try to characterize the local neighborhoods with ...
- 2,219
2
votes
Fitting rectangle to segments in image
You might be able to do better than simple gradient descent using an algorithm like BFGS, which uses the history of the gradients as well as the approximate solutions to try and approximate the ...
- 10.1k
2
votes
Accepted
What are the most popular wavelet or tight frame regularizers for image reconstruction problems?
EDIT: some code made available] From a personal experience, and in the work of colleagues, we observed that multi-band dual-tree wavelets, a type of low-redundancy oriented decompositions based on ...
- 466
2
votes
discrete definitions of curl $\nabla \times F$?
This is made a lot easier by introducing the Calculus of Finite Differences.
If $u_{i,j}$ is grid function defined for integer $i,j$ then the y-differencing operator
$$\delta_y u=u_{j+1}-u_j$$ is ...
- 1,084
2
votes
Open Source MRI Image Stacks
As I mentioned before, you can try with the Visible Human Project.
You can also go with 3D Slicer sample data, e.g., the Knee Atlas or the Brain Atlas. Their terms are quite permissive:
By ...
- 8,370
2
votes
Accepted
What are the numerical methods for testing for dissimiliarity between image based probability histograms?
Sounds like a job for the Earth Mover's Distance (or Wasserstein metric).
In computer science, the earth mover's distance (EMD) is a measure of the distance between two probability distributions.
...
- 379
2
votes
Automatic motion recognition
You would greatly benefit from knowledge in signal processing, but some specific useful knowledge would be in computer vision and estimation (like Kalman filters or alpha beta filters).
With respect ...
- 3,898
2
votes
Accepted
What is a good algorithm, and framework, to calculate centres of gravity or mass (cog)?
There are several alternatives:
Alternative #1: you need to find for each cell of the tessellation the list of pixels contained in the cell. To do that, you can use a rasterization algorithm. You can ...
- 2,305
2
votes
Is the inverse radon transform considered a linear operation?
For an operator $R$ to be linear, it has to satisfy two conditions:
$R(f+g) = Rf + Rg$ for any two operands $f,g$;
$R(\alpha f) = \alpha Rf$ for any operand $f$ and (real or complex) number $\alpha$.
...
- 54.1k
2
votes
Which technique to use for signal/image processing or noise removal?
You may start with median or Gaussian filters. There are many libraries that implement them and they are simple to use.
That said, I think this approach may be not enough because from what I've seen ...
- 121
2
votes
Which image filter acts like "surface tension"?
I think that you could use a Gaussian Filter.
The following Python code does something similar to what you show in your images.
...
- 8,370
2
votes
Algorithm to determine flat surfaces and camera orientation without specialized hardware
You are quite right, Augmented Reality benefits a lot from a combination of video/image analysis together with the data from motion sensors. Quote from Apple ARKit: Understanding World Tracking:
To ...
- 8,602
2
votes
Is there an efficient algorithm for matching objects in one image to objects in another?
I guess what you are referring to is the cross-correlation between the images. This is very good and efficient to find shifts, but not changes in scale and orientation. As you probably know, the cross-...
- 583
2
votes
Is there an efficient algorithm for matching objects in one image to objects in another?
Disclaimer: This is most likely not the most efficient, promising way to go about it.
When I was looking up the same topic from a similar interest (Analyzing microscopy images), I came across the ...
- 121
2
votes
Accepted
Polygon approximation with a circle
They just curve fit the two equations
$$
x(\omega) = h - b \sin(\omega) ~,~~
y(\omega) = k + a \cos(\omega)
$$
using a nonlinear curve fitting algorithm. However, the accuracy of the fit depends ...
2
votes
How applying the gradient descent method for solving a least square problem can remove the blur from an image?
The problem is equivalent to:
$$ \arg \min_{\boldsymbol{u}} \frac{1}{2} {\left\| \boldsymbol{G} \boldsymbol{u} - \boldsymbol{f} \right\|}_{2}^{2} $$
The solution is given by $ \hat{\boldsymbol{u}} = {\...
- 332
2
votes
Eigenvalue decomposition for a very huge matrix of medical images (such as the pixel physical coordinates of CT images)
Let us proceed systematically:
numerical precision of data (you said from medical imaging)
number of operations required for standard methods (as from libraries)
possible out-of-core computation (i.e....
- 21
2
votes
Accepted
First derivatives in Python Image Processing?
A gradient is not immediately well defined for digital images because they are both:
Quantized (the image values have a finite number of possible values E.g. 0-255 or likewise)
The image is ...
- 98
2
votes
Accepted
Calculating camera calibration matrix with Scilab
I found the answer. The videos I was looking at didn't mention a very important detail. The QR factorization needs to be applied to the inverse of the first three columns of P. The resulting K is also ...
- 131
1
vote
Poisson image blending artifacts
It seems I forgot to accumulate the boundary terms for each relevant entry in the right hand side vector $b$. So
...
- 141
1
vote
Image hash similarity matching possible?
Assuming you are talking about a cryptographic hash (as opposed to a hash used for speeding lookups, say), I think you are posing contradictory requirements.
The purpose of a hash is to remove any ...
- 139
1
vote
Methods to implement floor dirt detection algorithm
Here are some suggestions:
Whatever method you try, look at a large number of dirty floor samples to get an idea of the range of things - is it a darker area, is it streaks, etc.
For a simple idea, ...
- 139
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