make white image parts transparent?

i have an image like this:
http://www-mta-crl.fnal.gov/Entries/2008/07month/23day/12hour/Sandbox/Log/Text_22_0_radiation-symbol.gif
i assigned it as an image texture to a plane. how would i make it so the white parts would be transparent?

Quick solution in .blend file :

Attachments

transpwhite.blend (31.6 KB)

ok i’ll take a look at it. if you could write down what you did i’d be really grateful. thanks!

Setup:
ZTransp - ON
Alpha = 0
Alpha mapping set to yellow state to invert calculation ( under MapTo tab ) - this is key setting

CalcAlpha - ON to calculate alpha based on image RGB

OR

CalcAlpha - OFF
UseAlpha - OFF
This may produce smoother result especially with low-res images but may also produce lighter ( white ) borders.

thank you very much, works great!