The testing of Channel Four HD has begun on the free to view digital TV service Freeview.
This testing is taking place ahead of the proposed launch of Channel Four HD on the platform.
A test page is currently being transmitted on the Freeview platform, but only in certain regions.
The test page was first seen in the Crystal Palace area of London and then in the Granada TV area.
There are reports that the test may have been going on for some time.
When Channel Four HD is finally launched it will take the number of high definition channels offered on Freeview to three, following the launch of BBC HD and ITV HD last year.