diff --git a/gen_png.py b/gen_png.py
old mode 100644
new mode 100755
index 91e65b0..368c02b
--- a/gen_png.py
+++ b/gen_png.py
@@ -5,21 +5,97 @@ import ntpath
 import subprocess
 import sys
 import os
+# Dependencies: grep, git, inkscape, python 3.9
 
+
+# deletes raster graphics with given name
+def delete_graphics(name):
+    for f in name:
+        for d in glob.glob("./png/**/"+str(f)+".png", recursive=True):
+            print('deleting: ' +str(d))
+            os.remove(d)
+
+# rasters SVGs via Inkscape
+def raster_graphics(files):
+    sizes = [16, 32, 64, 128, 256, 512, 1024, 4096]
+    frogs = len(files)-1
+    for f in files:
+        name = ntpath.basename(f).replace(".svg", "")
+        print('\n------------------------------\n'+ str(frogs) + ' remaining...\nRastering ' + str(name)+'\n')
+        frogs = frogs - 1
+        for s in sizes:
+            subprocess.run(["inkscape", f, "-C", "-w", str(s), "--export-filename=./png/fixed_width/"+str(s)+"/"+name+".png"],timeout=30)
+            subprocess.run(["inkscape", f, "-C", "-h", str(s), "--export-filename=./png/fixed_height/"+str(s)+"/"+name+".png"],timeout=30)
+
+# git add given files
+def git_add_raster(files):
+    for f in files:
+        f = f.removeprefix('svg/').removesuffix('.svg')
+        stream = os.popen('git add ./png/**/'+str(f)+'.png') 
+        print(stream.read())
+
+# git commit given files
+def git_commit_raster():
+    stream = os.popen('git commit -m "[png] generate PNGs"') 
+    print(stream.read())
+    
+# create a new tag
+def create_tag():
+    # get tags
+    stream = os.popen('git tag -l "auto-v*"') 
+    output = stream.read()
+    tags = output.split('\n')
+    tags.remove('')
+    # create new tag
+    stream = os.popen('git tag auto-v'+str(len(tags))) 
+    print(stream.read())
+# -------------------------------------------------------------------------------------------------------------------------#
+# main section
+#
 files = list()
 if len(sys.argv) == 1:
-    files = [f for f in glob.glob("./**/*.svg", recursive=True)]
+    # get modified, added, renamed, deleted SVGs since last tag
+    stream = os.popen('git diff --name-status $(git describe --tags --abbrev=0 --match "auto-v*") HEAD | grep svg/')
+    output = stream.read()
+    files = output.split('\n')
+    files.remove('')
+
+    if len(files) == 0:
+        print('nothing to do!')
+        exit()
+    additions = [s.removeprefix('A\t') for s in files if 'A\t' in s]
+    modifications = [s.removeprefix('M\t') for s in files if 'M\t' in s]
+    deleted = [s.removeprefix('D\tsvg/').removesuffix('.svg') for s in files if 'D\t' in s]
+    renamed = [s.removeprefix('R100\t').split('\t') for s in files if 'R100\t' in s]
+    
+    # also delete the renamed files and regenerate with the new name
+    for r in renamed:
+        deleted.append(r[0].removeprefix('svg/').removesuffix('.svg'))
+        modifications.append(r[1])
+
+    #print('A:' + str(additions))
+    #print('M:' + str(modifications))
+    #print('D:' + str(deleted))
+    #print('R100:' + str(renamed))
+
+    delete_graphics(deleted)
+    git_add_raster(deleted)
+    print('\nAdditions:')
+    raster_graphics(additions)
+    git_add_raster(additions)
+    print('\nModifications:')
+    raster_graphics(modifications)
+    git_add_raster(modifications)
+
+    # commit and tag
+    git_commit_raster()
+    create_tag()
 else:
-    for f in sys.argv:
-        if os.path.exists("./svg/"+f+".svg"):
-            files.append("./svg/"+f+".svg")
+    if sys.argv[1] == 'all':
+        files = [f for f in glob.glob("./svg**/*.svg", recursive=True)]
+    else:
+        for f in sys.argv:
+            if os.path.exists("./svg/"+f+".svg"):
+                files.append("./svg/"+f+".svg")
+    raster_graphics(files)
 
-sizes = [16, 32, 64, 128, 256, 512, 1024, 4096]
-
-for f in files:
-    name = ntpath.basename(f).replace(".svg", "")
-    for s in sizes:
-        #subprocess.run(["inkscape", "-z", "-C", "-w", str(s), "-e", "./png/fixed_width/"+str(s)+"/"+name+".png", "-f", f])
-        #subprocess.run(["inkscape", "-z", "-C", "-h", str(s), "-e", "./png/fixed_height/"+str(s)+"/"+name+".png", "-f", f])
-        subprocess.run(["inkscape", f, "-C", "-w", str(s), "--export-filename=./png/fixed_width/"+str(s)+"/"+name+".png"])
-        subprocess.run(["inkscape", f, "-C", "-h", str(s), "--export-filename=./png/fixed_height/"+str(s)+"/"+name+".png"])