rt-ai YOLOv2 SPE on a Raspberry Pi using the Movidius Neural Compute Stick

Fresh from success with YOLOv3 on the desktop, a question came up of whether this could be made to work on the Movidius Neural Compute Stick and therefore run on the Raspberry Pi.


The NCS is a neat little device and because it connects via USB, it is easy to develop on a desktop and then transfer everything needed to the Pi.

The app zoo, on the ncsdk2 branch, has a tiny_yolo_v2 implementation that I used as the basis for this. It only took about an hour to get this working on the desktop – integration with rt-ai was very easy. The Raspberry Pi end was not – all kinds of version number issues and things like that. However, even though not all of the tools would compile, I just moved the compiled graph from the desktop to the Pi and that worked fine.

This is the design. The main difference here from the usual test designs is that the MYOLO SPE is assigned to node pi34 (the Raspberry Pi) rather than the desktop (Default). Just assigning the MYOLO SPE to the Pi saved me from having to connect a Picam or uvc camera to the Pi and also allowed me to get a better feel for the pure performance of the Pi with the NCS.

As can be seen from the first screen capture it worked fine although, because it supports only a subset (20 of 91) of the usual COCO labels, it did not pick up the mouse or the keyboard. Performance-wise, it was running at about 1fps and 30% CPU. Just for reference, I was getting about 8fps on the i7 desktop.

Completed ZeroSensors all ready for long term data collection

Finally this is a ZeroSensor all ready to go into full time service, capturing video, audio and environmental data. The goal is to use this data, and that from other cameras around the space, as training data for machine learning systems.

One specific goal is to create an anomaly detector with minimal supervision. As much as possible, it will learn from experience. This is kind of tricky as it requires detection of unknown length sequences depending on the circumstances. I am intrigued by the ideas behind the Universal Translator but not sure how much could carry over to this application. This paper reviews some of the techniques usually applied, at least for video processing. The situation here is a little different as there are quite different types of features involved. My plan is to preprocess video and audio to recognize salient features (using object detection or whatever) and then input these features, along with environmental sensor data, in the form of uniform time-slotted data sets to the anomaly detector. This doesn’t help with detecting the length of an interesting sequence – that’s the fun part of the project.

Integrating TensorFlow object detection into rt-ai Edge

I have been using DeepLabv3 for a while now for object detection but I thought it would be interesting to try some examples from the TensorFlow object detection repo. I now have an rt-ai Edge stream processing element that is based on the Jupyter notebook example in the repo. Presumably this will work with any of the models in the model zoo although I am just using the default one for now.

As you can see from the preview capture above (apart from the nasty looking grass on the left) it picks out the car happily, although not with a great confidence level. Maybe it doesn’t like the elevated camera position or the car is a bit too far away or a difficult pose – I will need to do some more experiments. With the preview display on (using PyGame) I am only getting 1 fps with 1280 x 720 frames from the camera which is a little disappointing. However, with preview turned off (the normal production mode anyway), I am getting over 15fps which is entirely adequate.

The capture above shows the raw image along with the object recognition data in the form of metadata rather than drawn on the image. This is actually pretty useful for both real-time and offline processing (such as a machine learning run). Capturing the original image does have the advantage that alternate object detectors could be run at any time, at the expense of having to store more data. Real-time actions can be based on the metadata and the raw image just discarded.

Anyway, definitely a work in progress. It will be interesting to see how it compares with the DeepLabv3 version as the implementation gets more efficient. What’s nice is that it is trivial to swap out one object detector for another or run them in parallel in order to run tests. Just takes a few seconds with the rtaiDesigner GUI.

Using blockchain technology to create verifiable sensor records and detect fakes

These days, machine learning techniques have led to the ability to create very realistic but fake video and audio that can be tough to distinguish from the real thing. The video above shows a very interesting example of this capability. The problem with this technology is that it will become impossible to determine if anything is genuine at all. What’s needed is some verification that a video of someone (for example) really is that person. Blockchain technology would seem to provide a solution for this.

Many years ago I was working on a digital watermarking-based system for detecting tampering in video records. Essentially, this embedded error-correcting codes in each frame that could be used to determine if any region of a frame had been modified after the digital watermark had been added. Cameras would add the digital watermark at source, limiting the opportunity for modification prior to watermarking.

One problem with this is that it worked on a frame by frame basis but didn’t ensure the integrity of an entire sequence. In theory this could be done with temporally distributed watermarks but blockchain technology provides a very nice alternative.

A simple strategy would be to have the sensor (camera, microphone, motion detector, whatever) create a hash for each unit of data (video frame, chunk of audio etc) and add this to a blockchain. Then a review app could create new hashes from the sensor data itself (stored elsewhere) and compare them to those in the blockchain. It could also determine that the account owner or device is who or what it is supposed to be in order to avoid spoofing. It’s easy to envisage an Etherium smart contract being the basis of such a system.

One issue with this is the potential rate at which hashes need to be added to the blockchain. This rate could be reduce by collecting more data (e.g. accumulating one second’s worth of data to generate one hash) or creating a hash of hashes at an appropriate rate. The only downside to this is losing temporal resolution of where changes have been made.

It’s worth considering the effects of lossy compression. Obviously if a stream is uncompressed or only uses lossless compression, watermarking and hash generation can be done at a very early stage. Watermarking of video is designed to withstand compression so that can still be done at a very early stage, even with lossy compression. The hash has to be be bit-accurate with the stream as stored on the video storage medium though so the hash must be computed after lossy compression.

It seems as though this blockchain concept could definitely be made to work and possibly combined with the digital watermarking technique in the case of video to provide temporal and spatial resolution of tampering. I am sure that variations of this concept are out there already or being developed and maybe, one day, it will be possible for anybody to check if a video of a well-known person is real or fake.

DroNet – flying a drone using data from cars and bikes

Fascinating video about a system that teaches a drone to fly around urban environments using data from cars and bikes as training data. There’s a paper here and code here. It’s a great example of leveraging CNNs in embedded environments. I believe that moving AI and ML to the edge and ultimately into devices such as IoT sensors is going to be very important. Having dumb sensor networks and edge devices just means that an enormous amount of worthless data has to be transferred into the cloud for processing. Instead, if the edge devices can perform extensive semantic mining of the raw data, only highly salient information needs to be communicated back to the core, massively reducing bandwidth requirements and also allowing low latency decision making at the edge.

Take as a trivial example a system of cameras that read vehicle license plates. One solution would be to send the raw video back to somewhere for license number extraction. Alternately, if the cameras themselves could extract the data, then only the recognized numbers and letters need to be transferred, along with possibly an image of the plate. That’s a massive bandwidth saving over sending constant compressed video. Even more interesting would be edge systems that can perform unsupervised learning to optimize performance, all moving towards eliminating noise and recognizing what’s important without extensive human oversight.

Convolutional recurrent neural network for video prediction and unsupervised learning

Very interesting work here that uses recurrent neural network ideas to predict next frames in a video sequence. It’s amazing how many times LSTM pops up these days. Unsupervised learning is one of the most interesting areas of machine learning at the moment and the potential is seemingly unlimited. This is another example of using LSTM for understanding video representations using LSTM. It’s a fascinating area.