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Show HN: API for detecting people, cars, and everyday objects in images

dextrorobotics.com

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Re: Show HN: API for detecting people, cars, and everyday objects in images

#31
post #24

Hey everybody, OP here. Thanks for the great feedback! We're really happy that so many people have checked this out. One thing that I want to mention: our service was built favoring Precision over Recall; we reasoned that we'd rather have a low number of false positives and make sure that when we do report a detection, that it actually is one. Thus, our service may occasionally miss instances. I'm going to implement…

You might want to let the user decide if it is more important to have a false positive or a false negative. For some applications a false alarm is a minor nuisance but a false negative is catastrophic, but for some applications it is flipped. In the past I have let the end user define the balance (i.e. "a false negative is 10X as bad as a false positive") and the decision results were scaled by their decision rule. It's not always easy to do as many machine learning algorithms are nonlinear but at least you can cast a wider net of potential customers.

Re: Show HN: API for detecting people, cars, and everyday objects in images

#32
Over a dozen experiments, the recognition rate for faces seems to be about 70%. Example of failure: only 2 faces detected here (in particular NOT the one in focus) http://iamdaveknockles.files.wordpress.com/2011/03/meeting_j...

This is worse than OpenCV (I thought you were using OpenCV but apparently aren't?)

Re: Show HN: API for detecting people, cars, and everyday objects in images

#33

Can you give me bit more technical background. Tell me how this is better than for eg. out of the box openCV filters.

It is probably based on "Object Detection with Discriminatively Trained Part Based Models"; Pedro F. Felzenszwalb"... Somebody took http://people.cs.uchicago.edu/~rbg/latent/ made REST API and hooked up a payment system.

Re: Show HN: API for detecting people, cars, and everyday objects in images

#34
Interesting technology. It got a couple correct for me. But failed on a bunch as well. Here's a few horses it failed to find correctly.

2 horses / detected 0: http://images4.fanpop.com/image/photos/23500000/horse-horses...

4 horses / detected all as 1: http://4.bp.blogspot.com/-Rso9vw4BmSE/TqZU6vHl3kI/AAAAAAAACL...

Re: Show HN: API for detecting people, cars, and everyday objects in images

#35

This reminds me of how my visual psychology professor was attempting to help those with poor vision 15 years ago, but didn't appear to get anywhere with at the time. The idea was a simple (but clever) one - use virtual reality to segment the world into solid blocks of identified objects. The solid blocks are identifiable to those with poor vision in a way that the real world is not. Essentially this meant processing…

However, attempt this today

According to http://news.ycombinator.com/item?id=4985100 it won't be today, perhaps tomorrow.

Re: Show HN: API for detecting people, cars, and everyday objects in images

#36
post #23

Earlier quoted context omitted.

One to two cents a task. Anytime you have a language agnostic task (identifying/classifying objects, etc), the tasks can be done very cheaply. Just make sure you do triplicate validation. Language dependent/creative tasks run much higher (smaller worker pool, more brain power needed).

I've never used mechanical turk before and don't understand what you mean by language agnostic. I'd want someone to tell me that it's a "car" and not a 汽車. And I'd want to give the instructions for the task in English.

If I had to guess what they meant: A car is a car, regardless if you call it 'car' or 'das auto.'

Re: Show HN: API for detecting people, cars, and everyday objects in images

#39
Didn't work for me. That said, image recognition via an API will be huge once things mature a little more.

I've been searching lately for a post-face.com API and have been following a few for a while, but they seem to have similar issues with poor results.

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