Unless you’re cheating and playing via an emulator on a PC, the Nintendo Wii can’t do high definition. One company, however, claims that by using its new device, it can
https://lastchance.cc/how-mario-galaxy-looks-in-720p-5308117/%3C/a%3E%3C/p%3E
This doesn’t mean the Wii game itself will be in high definition. It’s a “cheat”, just like many TV sets and DVD players (including consoles) are able to perform, called “upscaling”, where a standard definition signal is processed, then output as a (hopefully) cleaner image.
How well your device is able to upscale is up to, well, the device. Expensive TVs do a great job. So does the PS3. Cheaper DVD players, not so much. Chances are, if you have a HDTV, your set is already trying to upscale your Wii’s video signal.
For $75, then, you’d want to hope VDIGI’s converter is a damn good one. The screenshots on the company’s site, taken using a camera rather than a proper screen capture device, don’t look great (definitely not to the standard of the Dolphin emulator), but then for some people with crummy upscalers, it’ll still be an improvement.
https://lastchance.cc/how-your-wii-games-would-look-in-720p-452590262%3C/a%3E%3C/p%3E
VD-W3 Wii HDMI Upscaler Processor [VDIGI, via Go Nintendo]