Skip to main content

Kiwi Pycon

I have been looking at harris feature detection lately. Implementing it side by side in OpenCV and SciPy, luckily for me a SciPy implementation by Jan Solem was found on this blog. As I was going through the code, I wanted to get my head around what was happening. So using these two lines:
from IPython.Shell import IPShellEmbed
IPShellEmbed()()
This piece of magic can be put anywhere, right deep inside a nested loop, inside a function called from X via Y via Z etc. And it obviously pops you right into the brilliant IPython shell, with the full normal IPython luxuries like timeit, history, autocomplete, pylab plotting... So I plotted a few images midway through processing, just to see what the program sees.
First is the grayscale image taken from my webcam. No I'm not colour blind - I realize I have plotted it in colour.... Second and thirdly the two gaussian derivatives of the image, one in X and one in Y.




And a bit later after getting the thing going - the final output! Pretty cool to see how it came about with the two derivatives convolved together. Some filtering to choose spread out points (clearly not working) and then drawing dots! The code for this in OpenCV and in SciPy is here.

Oh and check it out - my first conference presentation!

Ahh, I'm going to have to prepare something now!

Popular posts from this blog

Bluetooth with Python 3.3

Since about version 3.3 Python supports Bluetooth sockets natively. To put this to the test I got hold of an iRacer from sparkfun . To send to New Zealand the cost was $60. The toy has an on-board Bluetooth radio that supports the RFCOMM transport protocol. The drive  protocol is dead easy, you send single byte instructions when a direction or speed change is required. The bytes are broken into two nibbles:  0xXY  where X is the direction and Y is the speed. For example the byte 0x16 means forwards at mid-speed. I was surprised to note the car continues carrying out the last given demand! I let pairing get dealt with by the operating system. The code to create a  Car object that is drivable over Bluetooth is very straight forward in pure Python: import socket import time class BluetoothCar : def __init__ ( self , mac_address = "00:12:05:09:98:36" ): self . socket = socket . socket ( socket . AF_BLUETOOTH , socket . SOCK_STREAM , socket .

Matplotlib in Django

The official django tutorial is very good, it stops short of displaying data with matplotlib - which could be very handy for dsp or automated testing. This is an extension to the tutorial. So first you must do the official tutorial! Complete the tutorial (as of writing this up to part 4). Adding an image to a view To start with we will take a static image from the hard drive and display it on the polls index page. Usually if it really is a static image this would be managed by the webserver eg apache. For introduction purposes we will get django to serve the static image. To do this we first need to change the template. Change the template At the moment poll_list.html probably looks something like this: <h1>Django test app - Polls</h1> {% if object_list %} <ul> {% for object in object_list %} <li><a href="/polls/{{object.id}}">{{ object.question }}</a></li> {% endfor %} </ul> {% else %} <p>No polls

Homomorphic encryption using RSA

I recently had cause to briefly look into Homomorphic Encryption , the process of carrying out computations on encrypted data. This technique allows for privacy preserving computation. Fully homomorphic encryption (FHE) allows both addition and multiplication, but is (currently) impractically slow. Partially homomorphic encryption just has to meet one of these criteria and can be much more efficient. An unintended, but well-known, malleability in the common RSA algorithm means that the multiplication of ciphertexts is equal to the multiplication of the original messages. So unpadded RSA is a partially homomorphic encryption system. RSA is beautiful in how simple it is. See wikipedia to see how to generate the public ( e , m ) and private keys ( d , m ). Given a message x it is encrypted with the public keys it to get the ciphertext C ( x ) with: C ( x ) = x e mod m To decrypt a ciphertext C ( x ) one applies the private key: m = C ( x ) d mod m The homomorphic prop