How do upconvert dvd players work?

Question

how can they take a dvd with 480p and turn it into 1080i?

Answer 1

A standard DVD player, without upscaling, can output video resolution at 720x480 (480i or standard definition, SD).

Upscaling is a process that mathematically matches the pixel count of the output of the DVD signal to the physical pixel count on an HDTV, which is typically 1280x720 (720p) or 1920x1080 (1080i - and, some cases, 1080p). Simply, upscaling DVDs can’t add new info, they create extra lines of pixels by copying parts of surrounding pixels, effectively "guessing" at what the image should look like at a higher resolution. If done badly, it can ruin picture quality. Its all done with algorithms on chipsets in the DVD player.

Not all TVs will do upscaling and depending on the model, not all do it well.  An upscaling DVD player is designed specifically to do this. There are several good ones on the market. I believe the Oppo brand is one of the best due the the Faroudja video processing technology chipset they use.

Answer 2

They just scale the video (same as you would scale up a picture) and they interpolate the pixels you don't have.

HDTVs can do exactly the same, so upconverting DVDs are pretty much a waste (unless you buy a really expensive one). However, at that point, it may be cheaper to get an HD or BD player.