The device is called a "Lyot Coronograph"; Sky & Telescope magazine; April / 2004.
Somebody else will have to dig up the URL.
But I now to confess that the HST lacks a Lyot Coronograph;
and I also now confess I can't see how "downlinked" HST images could be used effectively with a Lyot Coronograph [here on Earth] to "sift-out" the faint IR pixel of a jovian planet.
However, HST engineers have pulled off spectacular results before...
Jacob
"Extraordinary claims, require extraordinary evidence."
CARL SAGAN