A scanline mystery - help me solve it !

[Fudoh]

Ok,

here's a mystery which I just can't solve. Here are two screenshots from Metal Slug - emulated on a XBox1. VGA output into a RetroVGA unit ( http://www.brunofreitas.com/node/36 ) and then into another video processor for upscaling to 1080p (but that's not important). This is PhilExile's setup and he's insisting that the XBox is outputting 720p on the one shot and 480p on the other (unchanged until the signal gets into the RetroVGA).

Now, if the RetroVGA is anything like the SLG3000, then the device would add 360 scanlines to a 720p feed and 240 scanlines to a 480p feed. For 720p output the game/emu is set to linetripling, so every pixel gets exactly three lines (240p to 720p or 224p to 672p - rest filled up with black). The problem is that if you overlay 360 scanlines over an original 240p title, you would get a total misalignment of pixels versus scanlines (e.g. you would get 24 scanlines instead of 16 for a character sprite of 16 pixels height).

I say that either the RetroVGA does some magic and only applies one scanline to every THIRD pixel line (instead of every second as the SLG3000 would so) or the XBox is outputting 480p in both cases (which I would swear on), because both screenshots show totally perfectly aligned scanlines.

So, someone solve this mystery please

Alleged 480p screenshot:



Alleged 720p screenshot:



Thanks!

[philexile]

I swear on my Crystallio II I'm telling the truth!

The only thing I can think of is maybe the Startech VGA2TV2WAY is screwing with the signal somehow, but I don't think so. I can tell its 720p from the menus and not distorted at all. In order to rule this out, I may take it out of the chain and use the CII to transcode the signal to 720p, VGA and output directly to my TV. I'll try this later in the week.

[ikaruga007]

Wouldn't the scanlines be thinner if it was every third line in 720p? They look the same judging by those images so it does seem like both are 480p to me.

But I'm watching them on my phone so I may be wrong.

[philexile]

When it is in 720p mode, the image looks sharper. You can sort of see this in the photos.

[rugdoctor]

Any details on which emulator was used in each shot?

[antron]

notice the digit 1 has 7 lines in the 480p one and 6 lines in the 720p.

[fagin]

Fudoh you need some new glasses... those two pictures have totally different scanline alignments.

[Fudoh]

possible - likely due to less underscan on the lower example. Nevertheless none of the two resemble what scanlines using a SLG would look like on a 720p signal.

[Ed Oscuro]

Why does the "A" in "ARMS" have black "shoulders" (along the top) in the 720p versus the 480p screen? The 720p looks wonky as hell, but only on close inspection. And yeah, 6 scanlines versus 7...nice catch antron!

[moh]

Why does the "A" in "ARMS" have black "shoulders" (along the top) in the 720p versus the 480p screen?

wow, good eye. I barely noticed!

[matrigs]

phil aren't you changing the "width" switch on the arcadevga from thin to wide when changing modes ?

if so, the device blacks out every third and fourth line, which gives 192 lines on 720p.

[edit]

so when comparing it to the 240 lines of the original you get your 6 and 7 lines in the text. should be about right. 240/7 is 34, times 6 makes that 205 lines. so yeah that's about it.

[philexile]

It looks fine to me and I'm pretty picky. See below:

[Ed Oscuro]

It could be that motion shake is ruining some of your images, like your second one here appears to be. But I still wonder why there's those black portions of the original 720p screen.

[bootsector]

Hey Phil! I see you are enjoying your RetroVGA!

It looks like you are using it with the WIDTH switch positioned to DOUBLE instead of SINGLE, right? That makes the RetroVGA display 2 scanlines then blank the next other 2, and so on...

That setup is best suited for resolutions higher than 640x480!

bootsector

[Fudoh]

It looks fine to me and I'm pretty picky.

the white/orange 1UP lettering on top. Lowest row of pixels is a misalignment, since you should get one scanline for the lowest colored pixels and another one for the shadow row. On top of the row you can also see that there's a cut.

Still I don't get it. So we have a complete 720p chain from the source until the VP. How does the RetroVGA manage to handle the signal like that ??

[bootsector]

...
Still I don't get it. So we have a complete 720p chain from the source until the VP. How does the RetroVGA manage to handle the signal like that ??

I'm not sure on what do you mean here? RetroVGA is supposed to handle *any* VGA resolution.

Cheers,

bootsector

[Fudoh]

The RetroVGA is - just like the SLG3000 - supposed to insert a certain number of scalines, which is vertical resolution / 2, so for example 240 scanlines on a 480p signal, 360 scanlines on a 720p signal and 384 scanlines on a XGA signal.

Here we have 720p signal with scanlines that look nearly like those generated upon a 480p signal.

[matrigs]

It looks fine to me and I'm pretty picky.

the white/orange 1UP lettering on top. Lowest row of pixels is a misalignment, since you should get one scanline for the lowest colored pixels and another one for the shadow row. On top of the row you can also see that there's a cut.

Still I don't get it. So we have a complete 720p chain from the source until the VP. How does the RetroVGA manage to handle the signal like that ??

as mentioned before arcadevga has a mode where it blanks out the lines in a 11 00 11 00 11 00 11 00 fashion

the slg has no mode like this.

[Fudoh]

Ha, I failed to read your posting above!

That's it! I didn't know that about the RetroVGA. Nice feature though, as this would allow great scanlines on 960p as well, which on the other hand gives MAME and other EMUs much more resolution to work with.

Thanks for solving this mystery for me

[matrigs]

if you have minimum solder skills and are a little adventurous you can try to make this one by yourself:

http://www.mmmonkey.co.uk/console/other ... nlines.htm

at the very bottom you have explained how to make the additional width

[philexile]

the white/orange 1UP lettering on top. Lowest row of pixels is a misalignment, since you should get one scanline for the lowest colored pixels and another one for the shadow row. On top of the row you can also see that there's a cut.

Oh, you know, I may not have readjusted the screen position to match up to the scanlines exactly after I took the 480p pictures. I was pretty tired last night.

But I guess the riddle is solved, Fudoh?

[Fudoh]

if so, the device blacks out every third and fourth line, which gives 192 lines on 720p.

just to clear this up. We talk about 180 scanlines on 720p and 192 on 768p, right ?

[Fudoh]

Any idea if scanline width mod could be applied to a SLG3000 as well ? I would love to try some 960p emus, but I need the adjustable scanline density from the SLG3000.

[matrigs]

if so, the device blacks out every third and fourth line, which gives 192 lines on 720p.

just to clear this up. We talk about 180 scanlines on 720p and 192 on 768p, right ?

yeah something like this - my math is a little funky.

Any idea if scanline width mod could be applied to a SLG3000 as well ? I would love to try some 960p emus, but I need the adjustable scanline density from the SLG3000.

this is a question you should ask the arcadeforge team. the slg doesn't use the 74HC74 and 74HC125 at all, but an analog solution. to be perfectly honest i don't even know how the original slg works at all, if it also does blank out lines or it just displays an overlay or does something completely different. it is definitely a much more sophisticated solution than the "ghetto-slg" so that additional width might be impossible to do at all.

[bootsector]

if so, the device blacks out every third and fourth line, which gives 192 lines on 720p.

just to clear this up. We talk about 180 scanlines on 720p and 192 on 768p, right ?

yeah something like this - my math is a little funky.

Any idea if scanline width mod could be applied to a SLG3000 as well ? I would love to try some 960p emus, but I need the adjustable scanline density from the SLG3000.

this is a question you should ask the arcadeforge team. the slg doesn't use the 74HC74 and 74HC125 at all, but an analog solution. to be perfectly honest i don't even know how the original slg works at all, if it also does blank out lines or it just displays an overlay or does something completely different. it is definitely a much more sophisticated solution than the "ghetto-slg" so that additional width might be impossible to do at all.

http://nfggames.com/forum2/index.php?to ... 0#msg30650

As you can see, SLG3000 uses different components for achieving the same functionality (aside of doubling scanlines) found on the other cheaper/openhardware solutions.

bootsector