3) 720p forces either a 1:1 (1) or 4:3 (1.33) integer aspect ratio, neither of which looks correct for NES. You want something closer to ~1.22. With a windowed 1080p image you can get 5:4, which gives you a 1.25 integer aspect ratio.
So basically you have:
1--------------------------------1.22---1.25----------------1.33
Too skinny--------------------looks perfect--------------too wide
1080p makes integer scaling beyond 4x impossible without losing lines. And then you have to have the logic available to hit 5x. Which = more cost for the FPGA,.
720p is the far better choice since you can fill the entire screen with 3x scaling. Once upscaled to 1080p by the TV, then the image still will still look great. Also keep in mind the XRGBMini does not have 100% sharpness at 720p or even 1080p either. The signal is still soft as there is bleeding on pixel edges. You can look at MLIG's HDMI NES vs RGB video to see this. It looks similar to this comparison using MMLC
http://screenshotcomparison.com/comparison.php?id=142201 it looks similar to that. Which is honestly not that bad.
4k Tvs shouldn't even be considered in the equation, because even if it supported 1080p. The upscaling on most 4k TVs is not that great. (4k really came too early. 1080p TVs EOL and consoles still struggle with framerates at 1080p. Or even outputting 1080p consistently) And almost zero of them offer a line doubling 4:1 pixel mapping mode. Which is infuriating! We should really still only be in a 1080p era. The average person out there barely consumes any real HQ 2k content. Let alone 4k content. HD Cable is still a fucking joke. 1080i, 720p feeds that are ridiculously compressed. The only real benefit of 4k, is real true native 4k content on blu-ray on a very big screen. And Video Games on PC, if you can handle it. Or use it to downsample to 1080p for better AA. Because 4k native still does not solve aliasing issue in a significant way. Good luck hitting native 4k on the updated consoles on a regular basis. Scorpio might edge by barely. But we'll see.
In NIS's PC port of Phantom Brave, the sprites without the terrible bilinear filter are scaled on a non integer scale, causing scrolling artifacts. To fix it, you basically have to some driver level SSAA that just so happens to benefit the sprites and fills in the gaps with edge bleeding/gradients to make the pixels and scaling look more correct.
http://screenshotcomparison.com/comparison.php?id=180322 It does cost some sharpness, but it's not that noticeable (compared to the bilinear filter in the game)and in motion looks way better.
No method is going to look perfect, especially since not every CRT displays exactly the same. Getting the pixel aspect ratio perfect feels pretty impossible. You can try to aim for a 4:3'ish setting and that's about it.
And digitally stretching the image with nearest neighbor is going to result in scaling artifacts no matter what since the pixels being generated are still square.
That's what you are wanting to talk about. Not image aspect ratio. The *Pixel Aspect Ratio* is what is important in getting somewhat correct scaling close to a CRT.
After it's been padded correctly (Might be incorrect in 1.125 example below) cropped and then a PAR can be derived from a single individual CRT setup.
http://screenshotcomparison.com/comparison.php?id=143035 You can see that a 1.25 PAR (Should be near equivalent with padding removed) still works just fine at 720p
Edit: http://wiki.nesdev.com/w/index.php/Overscan According to this however, the correct PAR is actually 1.431
I should take a picture of my CRT running a NES game for example, it'd probably be slightly different as I have horizontal stretch set up customized through the service menu.
720p>1080p scaling is better than most 1080p>4k scaling i've seen.(720p>1080p is 1.5x1.5 in each direction = 2.25x. 1080p>2160p is 2x2 in each direction = 4x but they still use similar/same'ish upsampling methods. Which looks worse the higher the scale. A 4:1 line double mode could fix this) Plus, it might have the additional benefit of cleaning up any scaling artifacts if one attempts to use a non 1:1 mode trying to approximate the PAR as mentioned above and probably will end up looking similar to the XRGBMini at 1080p when doing so thanks to the filtering in upsampling. (Someone with an HDMI NES should test this.)
At the end of the day, The AVS is probably going to be the best, cheapest, hassle way free to play NES games on hardware that doesn't stolen emulation code and has never been improved. Or that isn't going to cost you 500$+
The NES HDMI Kit is 120$+install costs, has scaling artifacts when attempting to stretch the image to something resembling the correct PAR at 1080p. Can't recall if adds lag. don't think so.
The XRGB Mini is 400$+ requires a scart cable, the NESRGB be installed (Additional $$$). Hope nothing in your signal path is fucked that causes problems.
It does have the benefit of being able to stretch it any way you want without artifacts, but it does so with some kind of filtering. Also adds an additional frame of lag.
Analogue NT is 500$+, uses HDMI NES
Retro Game Freak costs between 200-300$+, basically the same as the Retron 5.(160$+) Stolen Retroarch, 720p only. Lagerific on many consoles.
AVS, 185$ requires nothing extra, 3x3 scaling with 1:1,4:3,5:3 SAR modes (I've yet to see a video of anything but 1:1 however), supports both FDS,Famicom and NES. 4 controller ports, Famicom controller port. And potentially next to zero lag from the console itself.
https://www.youtube.com/watch?v=9Tv1-vWKFjg
For the average person, if this is as good as it could possibly be. Then there's literally nothing better, and it should deserve to sell at such a low price for such quality compared to shit clones and the likes of the Shitron5. Which AFIK still only outputs at 720p with it's low powered Android SOC.