When a DVD is ripped to a file on a computer the dark scenes typically get compressed to the point of illegibility; huge squares of black are all set to the same value, removing all the detail. This is often seen in video files posted to the internet.
I get why it happens; The difference between two shades of black is quite easily to perceive, but to the compression algorithm it is a tiny difference, so the two shades are set to one value to save space.
However, this effect is obviously avoided on the DVD itself. How do they do this, and why don't the compression methods used when ripping the DVD to a file also do this? I mean, the DVD format and codecs are old, far older the the ones used online today. So why does this problem appear when ripping the file?