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Ancient secrets of computer vision

pjreddie.com

31–40 of 60 posts

Re: Ancient secrets of computer vision

#31
post #25

What's the best CV course nowadays that comes with videos, assignments, hws, etc.? It used to be the one taught by Justin Johnson at UMich [0]. But the publicly available videos have been last updated in 2019. [0]: https://web.eecs.umich.edu/~justincj/teaching/eecs498/FA2020...

I like Andreas Geiger’s lectures on U. Tübingen [0]. Quite recent, and I think the topics they cover are good.

[0] https://uni-tuebingen.de/fakultaeten/mathematisch-naturwisse...

Re: Ancient secrets of computer vision

#33
post #15

It's nice, but missing the most valuable (and simplest) take from computer vision: the Hough transforms. Let's take the circle Hough transform as it's one of the most enlightening ones! Say you are looking for a circle of a given diameter. After a binarization to make the edge stand out, make all the potential points "vote" for a circle center. The method is simple: using a matrix, you +1 all the points that are as f…

I will take the opportunity to call out one of my favourite libraries, BoofCV (http://boofcv.org)

It comes with a wonderful demonstration tool that allows you to apply the various included algorithms to images and tweak the parameters in real-time – including the Hough transform. A great tool for helping to understand how these kinds of algorithms work!

Re: Ancient secrets of computer vision

#34

While the content is definitely great, its outer looks are not so much. I am afraid I value whatever scraps of non-computer, human vision I still have left with me a tad more than learning those cool eldritch secrets... although the reader mode definitely helps.

Alternative opinion: The design of the site is a welcome breath of fresh air. Not every site needs gobs of whitespace, neutral colors and advertisements.

Re: Ancient secrets of computer vision

#36
post #5

Earlier quoted context omitted.

Hm. Do you think this is deliberate to filter out people with certain prejudices? Or do they genuinely think it’s a good design?

Countersignalling. By deviating from the “professional” look so ostentatiously, they signal that they are so good that they don’t need to use the usual look.

And then there are people like me, who seem to believe that if their resume spacing is off by a nanometer, then the entire world will view them as an unemployable failure.

Re: Ancient secrets of computer vision

#37
post #15

It's nice, but missing the most valuable (and simplest) take from computer vision: the Hough transforms. Let's take the circle Hough transform as it's one of the most enlightening ones! Say you are looking for a circle of a given diameter. After a binarization to make the edge stand out, make all the potential points "vote" for a circle center. The method is simple: using a matrix, you +1 all the points that are as f…

I agree it's very cool, but I have found it to be surprisingly poor in certain scenarios.

A "faint" circle will often score worse than 2 high-contrast parallel lines that happen to be the right distance apart, since the lines manage to trigger pixels along 20% of a circle's arc and their contrast massively inflates their score compared to the faint circle (higher edge pixel density).

It seems like there should be a simple way to weight the results by how dispersed within the circle's arc the pixels are, but I've never dug any further, after hitting this problem I had to move on.

Re: Ancient secrets of computer vision

#38
A really ancient secret, one of the grey beards I learned a lot from early in my career told me about how he got CV running on an Apple II way back in the day on the cheap. He decapped a DRAM, and carefully stuck a lens on it. They're not just susceptible to cosmic rays; without the package regular old visible light rays can cause bit flips too. If you look at CMOS sensors these days they actually have quite a bit in common with DRAM.

Re: Ancient secrets of computer vision

#39
post #15

It's nice, but missing the most valuable (and simplest) take from computer vision: the Hough transforms. Let's take the circle Hough transform as it's one of the most enlightening ones! Say you are looking for a circle of a given diameter. After a binarization to make the edge stand out, make all the potential points "vote" for a circle center. The method is simple: using a matrix, you +1 all the points that are as f…

As someone who does computer vision for a living, you're going to need to explain how this is:

1. The most valuable take from computer vision

2. The simplest take from computer vision

Not to mention this is rarely useful unless you're in a specific context where you're looking for circles in an image.

Re: Ancient secrets of computer vision

#40
post #15

It's nice, but missing the most valuable (and simplest) take from computer vision: the Hough transforms. Let's take the circle Hough transform as it's one of the most enlightening ones! Say you are looking for a circle of a given diameter. After a binarization to make the edge stand out, make all the potential points "vote" for a circle center. The method is simple: using a matrix, you +1 all the points that are as f…

I agree it's very cool, but I have found it to be surprisingly poor in certain scenarios. A "faint" circle will often score worse than 2 high-contrast parallel lines that happen to be the right distance apart, since the lines manage to trigger pixels along 20% of a circle's arc and their contrast massively inflates their score compared to the faint circle (higher edge pixel density). It seems like there should be a s…

My initial reaction is that adding an angle parameter would help. A circle should have votes from many angles while lines will vote from only a portion of the circle. With some added weight from angled convergence the faint circle could score higher.
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