In case you had the same trouble I had, ie, I couldn't get the given class to read and write the same file (the output file was corrupt).

I found a java class online that does the same thing, with different methods.

http://www.minworks.co.uk/stuff/GreyMap.java

You'll just have to edit it to make it work with PicData.java

Mine is working 100% now.  Good luck.