Measuring black in fonts

My roommate @Guiller is developing an experiment that attempts to measure the amount of black in the best selling fonts provided by a popular web. He asked me to help a bit by providing data analysis and visualization.
@Guiller developed some scripts in Java to scrap the information.
Basic data as follows:
> 192 fonts
> 25k pixels by font (average)
> 1 value of black by pixel
> black value normalized to interval 0-100%
Below some results of testing 4 fonts with Excel and R: