Sidequest: VGA scan doubler

[DoG]

[Smonson]

So I've been fiddling around with this one over the weekend and, although I am tooting my own horn here, I'm very pleased with the picture quality. The image is sharp, stable, and free from noise.

This is a close-up from a proper LCD monitor (not a TV like before) at low res:

lowres.jpg (252.85 KiB) Viewed 6097 times

And this one's from the same monitor at med res. Before, the med res version was fuzzy, but I changed something in the RAM read process and it suddenly improved a lot.

medres.jpg (244.6 KiB) Viewed 6097 times

The moire effect stuffs up the photos - there is no banding visible in real life. I just have no way to prove it!

I added support for 60Hz as well, but unfortunately I was 1 LE over the limit of 80 on this CPLD, so I've ordered some bigger ones and will continue the project when they show up. That extra room will also give me some space to add the scanline effect that everybody loves!

I also have a plan to pass-through monochrome automatically so that all 3 modes will work on a standard VGA monitor. I think that should be possible... But I'm going to have to do another version of the PCB for that, because I didn't think to break out the mono pin to the CPLD. But an interesting thought is that with all 3 modes supported, I could cut a few traces and route everything through the ST's normal monitor port, and have a "seamless" mod. The switchable VGA cables used for 15KHz monitors would then work, but with more monitors. As you can see from the earlier pic of my mod board I've got my own r-2r ladder DACs on there and header pins for the VGA socket. But theoretically, I could just inject the video back into the shifter socket and go through the ST's video DACs (including mono). Probably I'd have to change some resistor values because of the voltage difference (3.3v instead of 5v). I'd have to cut tracks (or find some component I can unsolder) to inject HSYNC and BLANK signals in place of the Glue-generated ones. I think I'm going to take this idea as far as it goes.

[Icky]

Nice progress @Smonson

[derkom]

The moire effect stuffs up the photos - there is no banding visible in real life. I just have no way to prove it!

I've found the easiest way to prevent moire when photographing an LCD is just to step back far enough that each physical pixel in the camera sensor is going to be more than one pixel on the display, then crop the photo down. Sure, it sacrifices a little bit of the ability to duplicate the full resolution of the display, but we're not talking about displaying that kind of resolution here anyway.

[PhilC]

Thats a nice looking screen, well done @Smonson

[troed]

I could cut a few traces and route everything through the ST's normal monitor port, and have a "seamless" mod.

That's a really cool idea. Add your TOS 1.04 multi-res patch (and the same then done to the 2.06 source) and we have all resolutions reachable from within GEM to any VGA-capable screen.

Awesomeness.

/Troed

[Smonson]

I've found the easiest way to prevent moire when photographing an LCD is just to step back far enough that each physical pixel in the camera sensor is going to be more than one pixel on the display, then crop the photo down.

That's a good idea. Although I don't think I have a big enough room to do that with my 48MP phone camera. I might have an older camera in a drawer somewhere that would work. I'll give it a try next time! Thanks!

[sandord]

I'm sure you could dial down the resolution on your phone?

[agranlund]

If you find yourself lacking stuff to do, then it would be neat if it would take the DE signal and a switch to enable/disable the borders in the output image

I'm thinking the borderless image is probably much more likely to end up being a multiple of native monitor resolution so would yield a sharper image in addition to better screen coverage.

[exxos]

That's not a bad idea really. I wonder if the system will run slower with it having more video data access to RAM on full screen though..