[TYPO3] converting image to greyscale

[Amiran Chyb]

Hi there

I have an impression that I've seen TS option to convert image to  
greyscale - is it just my imagination?

I'd like to do it in tt_news teasers (teaser - b&w, full view - color).  
I'm sure sombedy's done that or something similiar (i.e. custom img  
processing) - could you point me the right direction to do that? (maybe  
some existing ext, user function, abything)

thanks
Am