Thursday, June 13, 2013

Latex formulas as images using Python

I find it endlessly frustrating to incorporate math into vector-graphics documents and Powerpoint presentations. While Powerpoint does allow importing equations from the equation editor, they usually look terrible.  However there is an online Latex equation editor run by that allows you to generate images of expressions.  This works great, but it's inconvenient to save and regenerate images after using it.

To that end, I've written a python function that will generate the URL for the Latex image-generation script, get the image data using HTTP and write it to disk as a file of your choosing.  It uses the python requests module (available via pip) and ImageMagick:

import os, requests

def formula_as_file( formula, file, negate=False ):
    tfile = file
    if negate:
        tfile = 'tmp.png'
    r = requests.get( '\dpi{300} \huge %s' % formula )
    f = open( tfile, 'wb' )
    f.write( r.content )
    if negate:
        os.system( 'convert tmp.png -channel RGB -negate -colorspace rgb %s' %file )

The code is appallingly simple for how much time it has saved me; it allows me to regenerate formulas for conference posters by simply running a python script and since most vector-graphics packages simply link to bitmap images allows the resulting layouts to update automatically.  Even better is that CodeCogs image generation script produces transparent PNGs so you can drop them on top of lightly colored backgrounds.  By setting the negate flag you will get a white on transparent PNG that can be used over dark backgrounds.

Here are some examples:

formula_as_file( r'\Gamma_{Levin}(x) = \| \nabla p(x) \|_2^{0.8} + \sum_i |\frac{\partial^2 p(x)}{\partial x_i^2}|^{0.8}', 'reg_levin.png', True )

formula_as_file( r'\Gamma_{MTV}(x) = \| \sum_{i=1}^3 \left( \| \nabla p^{(i)}(x)\|_2^2 \right) \|_2', 'reg_MTV.png' )

Finally no more ugly power-point presentations!

1 comment:

Junjie Fan said...

Very useful. Thanks James