DVD double

With DVD double the vertical pixel rate to HD quality – how effective is this in practice.

There was a RO module that changed mode 13 into mode 28 on the fly.

Does the ‘Pi’ do something similar?

With DVD double the vertical pixel rate to HD quality – how effective is this in practice.

Depends upon what you expect the end result to be.

It doesn’t take much interpolation to convert an anamorphic 720×576 image to 1280×720. Since this is a British site, we’ll assume PAL and not that low quality junk called NTSC. ;)

It is a little bit more work to make a FullHD image (1920×1080) however when you’re working with the raw MPEG data, various tricks can be used to smooth the picture so it doesn’t look like a simple doubling up.

I think the main stumbling block (and why cheap players do a lousy job) is because proper HD types are followed by a little “p”, like 720p and 1080p.
This means progressive scanning – the entire picture is drawn from top to bottom.
DVDs are based on older television standards, and are interlaced. This means half the picture is drawn (like every even line), then it goes back and fills in the gaps (every odd line). This was originally done in order to get a screen drawn as quickly as possible within a limited bandwidth. If it wasn’t interlaced, it would either require vastly more bandwidth, or it would take too long and flicker terribly.
This is why, incidentally, broadcast television uses 1080i (interlaced) for the FullHD. It halves the bandwidth necessary.

However, the problem arises when you consider the frames as being fixed points in time. Therefore the two halves of an interlaced picture won’t necessarily match up. So pasting them together to create a single image will result in comb artefacts around the parts that have moved.
This is VERY obvious (to me) when watching a recording of a 1080i broadcast on my computer or phone, which are progressive scan devices. There are various algorithms to try to reduce the effect, but they are only of limited application as you can’t easily recreate what isn’t there.

So – the actual scaling up isn’t really an issue. Except for small on-screen captions and end credits (that will appear to wobble) and fine details that will be a bit blurry, you probably won’t really notice much difference between 720 and upscaled 576. Upscaled to 1080, it’s probably passable if details aren’t that important (think any movie with Dwayne Johnson).
The issue you’re more likely to notice is the interlaced to progressive conversion, and this depends upon the quality of your hardware and/or software.

Oh, and let’s not forget there’s some extra fun in there too if you’re using a computer. The speed of DVD refresh (25fps) versus monitor refresh (typically 60fps minimum). Again things changing in time in awkward ways…

Comb artefacts – it’s a bit extreme looking as this is zoomed up (and faked), but it gives you an idea of what I mean, if you aren’t sure…

Example with overly long URL

The speed of DVD refresh (25fps) versus monitor refresh (typically 60fps minimum).

This is why a 4K TV is better than a 4K monitor if you’re trying to use a pre-Pi4 Pi (or an oldish Mac Mini) in a 4K mode – the TV has no trouble handling 25fps (2160p or 2160i).

There was a RO module that changed mode 13 into mode 28 on the fly. Does the ‘Pi’ do something similar?

You can configure your Pi to work in a fixed resolution and let the Pi’s graphic processor do the scaling from the selected mode to to the real resolution. In combination with !AnyMode it also allows you to use low resolution modes (but not < 256 colors) not directly supported by your monitor.

For DVDs, you can play them with !KinoAmp in combination with the VideoOverlay module. Overlays on the Pi can directly display and scale YUV images on top of the screen which gives a big speedup. Without it !KinoAmp struggles a little on the PI3 to upscale the video to FullHD when using bilinear filtering. !KinoAmp also performs de-interlacing which camouflage the combing effect mentioned by Rick by blurring the image. Without that trick some DVDs are simply unwatchable.