GOOD PHOTOS: (NTSC-J Saturn over composite on Sony Trinitron KV32FS120)Standard definition NTSC video is 720x480 pixels at 60 interlaced fields (not frames) per second. When viewing 480i content on an interlaced display, the picture is displayed and updated somewhat like this. The picture is divided into two fields: one for the odd numbered lines and one for the even numbered lines. The TV refreshes the odd field at one moment, then the even field 1/60th of a second later, and then alternates back and forth. This is how SD video content and displays generally operate.
Classic video game consoles work slightly differently. Generally, their graphics hardware wasn't robust enough to utilize a full 480 resolution at once, so most of them output 240p video instead of 480i (usually), like so. This only uses one field, but it's still updated at the same 60hz rate as normal SD video. The other field is left blank, creating what are often referred to as scanlines.
That's fine on old TVs that are interlaced by nature, but this stuff can lead to problems when we're using progressive scan equipment, which basically includes every consumer flatpanel TV and monitor. Progressive TVs process an entire frame at once instead of alternating fields. This means that 480i60 video is basically fed into the TV like this.
Modern TVs tend to have a built-in deinterlacing process to account for this by splitting the fields apart and doubling their resolution before they're even displayed, producing something that ideally looks a little more like this. Unfortunately, this has some drawbacks. The picture quality isn't always great due to the guesswork involved in resolving the two fields, and it takes time for a TV to apply all of that processing to the image before it gets displayed. This can result in a very significant amount of input lag. (And perhaps contrary to popular belief, it is this deinterlacing process, and not upscaling per se, that often accounts for a lot of extra input lag when playing retro video game consoles. Upscaling lag is also a concern of course, and that also can vary significantly between TV sets, but you can often eliminate a significant chunk of lag by making sure that you feed the TV a progressive signal in the first place instead of forcing it to handle an interlaced one. If you're in the market for a new HDTV and want to make sure that it has low input lag in general, check out sites like displaylag.com.)
The other major drawback is that a lot of modern TVs have no way to distinguish between 240p and 480i content! They assume that 240p consoles are actually sending a 480i signal, so they'll still go through all of this deinterlacing junk and add extra processing to the signal that doesn't have to happen! Some TVs can correctly identify 240p content, but many can't do it at all.
Finally, most HDTVs are just bad at upscaling a 240p image to their native resolution. Between a lot of questionable post-processing that you may or may not be able to turn off and internal scalers that just aren't built with an eye for pixel art, you're usually going to get something that looks bad or worse if you plug an SD video game console straight into an HDTV.
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DISCUSS
