2x scaling and scanlines

[Dave Dribin]

I've been reading Des Jone's modeline tutorial, and I've got an idea I'd like to bounce off people who are more knowledgable than I.

Say I'm trying to emulate Gauntlet, which runs at 336x240 @ 60Hz, and I've got a multisync CGA/VGA monitor (D9200 or equivalent).  If I want to get pixel perfect emulation, I'd need an ArcadeVGA, AdvanceMAME with a supported video card, or PowerStrip and supported video card.  If my video card cannot do low pixel clocks, I can double the horizontal resolution to 672x240 @ 60Hz and it will be visually indistinguishable.

But what if I also double the vertical and use 672x480 @ 60Hz.  According to Des's tutorial (page 7), this results in an inaccurate scanline, since each line is drawn twice.  But what if, instead of drawing each line twice, every other line is drawn black.  As this results in 336 actual lines displayed, would it be visually indistinguishable from the original 336x240?  It seems to me that it would be.

The only issue I can think of is that each visible line would be drawn in half the time.  I'm not sure if this would affect the brightness, but I don't think it would, as the color voltages are fine.

As to how draw black lines every other line... just use "-effect scanlines", but use white and black stripes, instead of white and gray.

Does this make any sense, or am I just babbling incoherently?

-Dave

[richms]

Yes, you make sense, but you would need to tweek the focus of the monitor to widen up the beam somewhat so that it didnt look like alternat scan lines were being drawn, and dont try this on a tv out since that will go thru an interlacer which will most likly smooth it out into a very dim flickery image.

I photoshopped this for the start screens and stuff of the emulator, but I want the higher res'es to be properly visable so dont want to mess with the focus, in fact I dont even know if you can on modern computer monitors.

I found best results in game were at 1600x1200 or the next one up with the scanline effects turned on in mame.

[Dave Dribin]

Why would the focus need tweaking?  Does the focus change, depending on the horizontal frequency?  As long as you have a monitor with high enough dot pitch, you won't see the blank scan lines.  You're right, if you do this on a high dot pitch monitor, like a normal PC monitor, you will definitely see the scan lines.  But on a D9200 or equivalent, you won't even notice.

BTW, if this trick works, I see no reason to even try the 15kHz modes, as I can get just as authentic results using 2x scaling + scan lines at VGA resolutions.  The benefit is that machines not capable of using an ArcadeVGA can get the same results, so long as you have a VGA capable arcade monitor.

-Dave

[tetsu96]

Why would the focus need tweaking?  Does the focus change, depending on the horizontal frequency?  As long as you have a monitor with high enough dot pitch, you won't see the blank scan lines.  You're right, if you do this on a high dot pitch monitor, like a normal PC monitor, you will definitely see the scan lines.  But on a D9200 or equivalent, you won't even notice.

BTW, if this trick works, I see no reason to even try the 15kHz modes, as I can get just as authentic results using 2x scaling + scan lines at VGA resolutions.  The benefit is that machines not capable of using an ArcadeVGA can get the same results, so long as you have a VGA capable arcade monitor.

-Dave

I think he suggested the focus as it would widen the beam a bit / overlap where scanlines would be otherwise.  It's not something that can be done per game, and I wouldn't do that myself.

As to playing with resolutions, pure black scanlines are very noticable in my opinion on the betson multisyncs and some others.  I'd go for doubling the vertical resolution and a scanline2x effect.  Every line of the game is drawn twice, and the 2nd is 1/2 brightness.  Scanlines shouldn't really be THAT visible if you can help it and even the multisyncs look off when using black scanlines.

I haven't used a D9200, so YMMV.

[Dave Dribin]

As to playing with resolutions, pure black scanlines are very noticable in my opinion on the betson multisyncs and some others.

With a Betson+ArcadeVGA, do people not run in low vertical resolutions?  If you use a low vertical resolution on a Betson, say x240, the black lines would be just a noticeable, right?

-Dave

[tetsu96]

As to playing with resolutions, pure black scanlines are very noticable in my opinion on the betson multisyncs and some others.

With a Betson+ArcadeVGA, do people not run in low vertical resolutions?  If you use a low vertical resolution on a Betson, say x240, the black lines would be just a noticeable, right?

-Dave

They certainly can if they want.  I don't use an AVGA with my Betson, but games look more natural IMO with the vert resolution doubled up and the RGB scanline2x effect applied with my AdvanceMAME setup.  If the dot pitch was worse by setting the monitor slightly out of focus, then this may not be the case.

Again, YMMV so test a few modes out yourself as you have to be happy with your setup.