Hello to all,
Stupid question, years ago I had an old analog oscilloscope, it had not only 2 usual modes "Y versus Time" and "Y versus X", but also had Z input, where I can put any signal to change electron beam intensity and thus vary trace brightness.
As a result I could for example make an simple analog TV from oscilloscope, putting AV signal to Z input and horizontal + vertical raster signals to usual 2 X Y channels.
Nowadays I see no modern 4 channel oscilloscope with this feature.
Oscilloscope makers could for example make a feature, to put 1 and 2 channel to X and Y, then 3rd channel to brightness, (and 4th channel to color of the trace). May be there's no practical engineering application, but this could be a big fun to play with.