Continuous gray rendered as bands of differerent shades of gray

vbimport

#1

Imagine looking out at the horizon at twilight on an overcast day. And picture in your mind how the gray of the twilight sky imperceptibly shifts from light gray at the horizon to dark gray overhead.

Now imagine that instead of the gradual and continuous transition from light gray to dark gray, the twilight sky were instead divided into a number of horizontal bands, each one a distinctly different shade of gray, ranging from very light gray at the horizon, through light gray, medium light gray, medium gray, medium dark gray, dark gray to very dark gray overhead.

That’s how my TV renders what should be a continuous shift in tones whenever there’s a fade in or fade out in the movies I play on my DVD player.

Can someone tell me what that tonal banding effect is called? I Googled it a couple of days ago and found that it does have a name and that there is a remedy for it. But now I can’t seem to find the web page with that info (and I can’t remember what search string I came up with that turned up that info).

And more to the point, can someone explain to me how it might be corrected?


#2

Posterisation.

There are several possible causes, including the deficiencies/limitations of the screen, but in this case it is almost certainly an inescapable artefact caused by the lossy compression of the video.