Extracting values from images

[fifi]

I've been using cacti for almost a year and am very pleased with it. I started using it because it made rrdtool so simple to configure and use. I was wondering if someone could help me with this one..

I have several graphs of the type "Interface - Traffic (bytes/sec, Total Bandwidth)". At the bottom right these graphs is the total transferred input and output. Is there a way I could extract those using 'rrdtool xport', or something similar, into a text format that I could then display on a web page, or send in an email? I'm having trouble following the 'sum' operation that is setup in the graph template. Thanks!