convolve

Simple demonstration of separable convolutions. This includes a standard gaussian blur, and a more recent lens blur using complex kernels. This is a demo project only, it could contain errors!

Gaussian Blur

I've written this in python 3 using cython for a significant speed boost. In most cases if you want to use convolutions you're safer using a library like numpy or opencv. These tend to use a fourier transform for large convolutions, so I avoided them here just to show the performance benefits.

Python

To run this code you'll need python 3, and cython installed. I've used this in linux, it should port fairly easily to other operating systems. Cython in windows is a little more difficult, but doable!

Compiling with Cython

Cython compiles your (almost) python into C, which you then compile into a python module. You can compile using cython like this:

cython -a compute.pyx

The -a flag outputs a nice HTML file showing where C and Python interact. I've optimised this code for C, so there aren't many yellow lines. It was a lot worse when I started!

This will produce a c file, which you compile using something like this:

gcc -shared -pthread -fPIC -fwrapv -O2 -Wall -fno-strict-aliasing -I/usr/include/python3.6m -o compute.so compute.c

Notice you need to point the compiler ar your installed python headers - which may not be in the same place as mine.

If compilation is successful, then you'll obtain a compute.so file, which can be imported from python as normal. Windows compilation will be a little more complex, as gcc isn't available to you. Here might help!

Running the code

You can run the code like this:

python run.gaussian.py --sigma 3.0 ./christmas.jpg ./christmas.out.jpg

My included christmas tree picture is fairly large, so even a small convolution will take a while. You'll see quite a difference if you run this with the --no_separable_filters option though.

Lens Blur

This is also written in python 3, without cython this time. Complex convolutions aren't too difficuly, but I decided the scypi library was easier here. This lens blur is the sum of a number of components, which means that the time taken scales linearly with the number of components you wish to use. Larger images with high component counts will take a fair while!

Running the code

You can run the code like this:

python run.lens.py --radius 50 --components 3 --exposure_gamma 3 ./M35.jpg ./M35.out.jpg

I found numpy raises memory issues if you use very large images, avoiding the stack function would probably fix this, but I decided not to worry about it.

One interesting difference between this simulated lens blur and a real lens is that the lighting works differently. I used a gamma-like function to increase the exposure prior to convolving, and then reverse this afterwards, I found this tends to highlight the brighter areas of the image, but results will depend on your settings, and the image you are filtering.