Export a sequence of LaTeX equations to individual image files

equations.tex

% quad %
\[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]

% optimization %
\usepackage{amsmath}
\begin{equation*}
\begin{aligned}
& \underset{x}{\text{minimize}}
& & f_0(x) \\
& \text{subject to}
& & f_i(x) \leq b_i, \; i = 1, \ldots, m.
\end{aligned}
\end{equation*}

scrape_latex.py

#!/usr/bin/python
import re
import sys
import tempfile
import subprocess
import os

def export_equations(filename,dest='./',dpi=300):
    
    with open(filename,'r') as f:
        s = f.read()

    names = [ dest+re.sub('[\W_]','',n) for n in re.findall('%.{,}%\n',s) ] 
    eqns = re.split('%.{,}%\n',s)[1:]
    tmp_name = '.tempfile_latex_to_png'

    for outfile,eq in zip(names,eqns):
        # make temporary file
        temp = open(tmp_name+'.tex','w')

        packages,body = [],[]
        for eqline in eq.split('\n'):
            if eqline.startswith('\usepackage'):
                packages.append(eqline)
            else:
                body.append(eqline) 

        # write equation
        temp.write('\documentclass[preview]{standalone}\n')
        [ temp.write(pkg+'\n') for pkg in packages ]
        temp.write('\\begin{document}\n')
        temp.write('\pagestyle{empty}\n')
        [ temp.write(line+'\n') for line in body ]
        temp.write('\end{document}\n')

        # compile latex
        temp.close()
        subprocess.call(['pdflatex','-interaction=nonstopmode',tmp_name])

        # crop pdf, convert to png
        subprocess.call('pdfcrop %s.pdf %s.pdf'%(tmp_name,outfile),shell=True)
        subprocess.call('convert -density %i %s.pdf %s.png'%(dpi,outfile,outfile),shell=True)

    # delete all temporary files
    subprocess.call(['rm', tmp_name+'.tex'])
    subprocess.call(['rm', tmp_name+'.pdf'])
    subprocess.call(['rm', tmp_name+'.log'])
    subprocess.call(['rm', tmp_name+'.aux'])

if __name__=="__main__":
    fn = 'main.tex' if len(sys.argv)<2 else sys.argv[1]
    df = './' if len(sys.argv)<3 else sys.argv[2]
    dpi = 300 if len(sys.argv)<4 else sys.argv[3]
    export_equations(fn,df,dpi)

Running $ ./scrap_latex.py from the command line should produce two files:

quad.pdf

optimization.pdf