Faster Image Transforms With Cython

Graphical depiction of going from Python to Cython

This is the second post on how to accelerate Python with Cython. The previous post used Cython to declare static C data types in Python, to speed up the runtime of a prime number generator. In this post we shall be modifying a more complex program, one that performs an image transform on a map. This will allow me to demonstrate some more advanced Cython techniques, such as importing C functions from the C math library, using memory views of Numpy arrays and turning off the Python global interpreter lock (GIL).

As with the previous post, we shall be making a series of Cython modifications to Python code, noting the speed improvement with each step. As we go, we’ll be using the Cython compiler’s annotation feature to see which lines are converted into C at each stage, and which lines are still using Python objects and functions. And as we tune the code to run at increasingly higher speeds, we shall be profiling it to see what’s still holding us up, and where to refocus our attention.

Although I will be using Python 3 on a Mac, the instructions I give will mostly be platform agnostic:  I will assume you have installed Cython on your system (on Windows, Linux or OS/X) and have followed and understood the installation and testing steps in my previous post. This will be essential if you are to follow the steps I outline below. As stated in the previous post, Cython is not for Python beginners.

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Transverse Mercator With Python

Geographical Mercator map of the world, without countries or gridlines

With global warming melting the icecaps and opening up the poles for oil exploration and tourism, I think it’s time for a new standard wall map, one that shifts those distorted map regions away from major land masses, and places the polar regions where we can see them. That way, our cruise ship and oil tanker captains can navigate more easily through the clear, blue Arctic Ocean, unimpeded by any tiresome ice-pack.

I particularly love that oil companies want to use the new Arctic Ocean sea lanes to transport their oil to market faster. Is it irony, or some form of rare, extinction-level stupidity that only comes around one every few thousand years? Hard to tell. But I digress.

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