Update README.md

README.md

@@ -11,6 +11,36 @@ The files are in the public domain and were obtained from
 The repository contains:
 
   * SVG images in `svg`.
+  * PNG inages in `png`:
+    - 256 pixel wide images in `png/256`.
+    - 512 pixel wide images in `png/512`.
+
+Images at any resolution can be created rasterising the SVG files.
+
+Rasterising SVG Files
+---------------------
+
+On Apple OS X SVG files can be rasterised using `librsvg`, which can be
+easily installed using [MacPorts][macports]:
+
+    $ sudo port install librsvg
+
+An SVG file can be rasterised using the following command:
+
+    $ rsvg-convert [options] name.svg -o name.png
+
+The images in `png` were created using the following command (executed in the
+repository root directory):
+
+    for res in 256 512
+    do
+      for i in svg/*.svg 
+      do
+        IMAGE_NAME=$(basename $i .svg)
+        rsvg-convert -w ${res} $i -o png/${res}/${IMAGE_NAME}.png
+      done
+    done
 
 [iso3166a2]: http://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
 [commons]: http://commons.wikimedia.org/
+[macports]: http://www.macports.org