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Author Topic: Questions on Dreamcast video  (Read 4682 times)

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Stormdemon

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Questions on Dreamcast video
« on: August 02, 2003, 06:08:43 pm »
I'm using a PAL Dreamcast on a Scart TV with a real RGB cable and I have a few doubts about some issues regarding my console. I'm asking here becasue I'm sure there are people in this forum with enough knowledge and experience to answer these questions.

When I'm using my DC on my PC monitor via VGABOX, my console is displaying 640x480 at 31khz (as indicated in the OSD of my monitor). Correct? Now, I guess this is the same frequency used in Naomi cabinets, which have Arcade mointors capable of accepting video at 31khz, right? In fact, if you stare at those monitors you cannot see scanlines, as you cannot see them in a PC monitor. I suppose the picture in those Arcade monitors is non-interlace, right? But when I use my DC on the TV with the RGB cable, the picture is interlace. I guess it's interlace because a TV cannot accept 640x480 non-interlaced, am I wrong? I also assume the signal is sent to the TV at 15khz, correct? The interesting issue is that some low res games such as Last Blade 2 or SFIII double impact display non-interlace picture (more stable display and perfectly visible quiet scanlines). Would it be possible to have this non-interlace display with 640x480 games? And why other games such as SFIII third strike, which is also low res, display interlaced picture (no quiet scanlines). Could I change it to non-interlace with some hacking to my RGB cable?

And that's all. All I'd like to know is whether I can have 15khz non-interlace display in all Dreamcast games, be it on a Scart TV or an Arcade monitor, and what do I have to do to achive this. Or at least, if anyone knows how to display the incredible SFIII third strike with the same beautiful scanlines that happen with SFIII double impact. The picture of the Dreamcast with the RGB cable is superb, but it could be even better at 15khz non-interlaced. I guess it must be possible, because otherwise, how to users of low res Arcade monitors use their Dreamcast in their cabinets? If there's any DC user who has build a cabinet with this console, please let me know what you had to do for using it with your monitor, and what kind of picture you obtain in your Arcade monitor (interlace or non-interlace).

Thank you very much.

Dave_K.

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Re:Questions on Dreamcast video
« Reply #1 on: August 03, 2003, 08:16:22 pm »
I believe I answered this in one of your older threads.  But I'll post it again since you went to great lenghts to detail your question a second time ;D.

Arcade monitors (standard res), SCART  TVs, and normal TVs are all 15khz interlaced display devices.  There is no way to display a non-interlaced picture on these monitors.  Because of the interlaced picture (1 frame is actually drawn to the display twice as 2 fields) scanlines in the picture are sometimes very apparent (depends on the game).

VGA (640x480) 31khz, otherwise known as 480p in HDTV terminology is a non-interlaced signal.  Only high resolution arcade monitors, or HDTVs can display this non-interlaced picture.  These monitors typically have smaller dot pictches than TVs and obviously don't need to draw 2 fields per frame.  Thus this picture looks much more solid/stable.  And there are no scanline artifacts (except if the game does this on purpose...see below).

Now, when it comes to games, scanlines may be very apparent on 15khz displays.  But the game developer could also have exaggerated these scanlines in the software intentionally (much the same way MAME can simulate scanlines).  This may help the game actually play faster (it has less pixels to display per frame).  The older fighter games you mentioned happen to fall into this category.  The scanlines may be VERY apparent on 15khz displays, and also apparent on 640x480 VGA displays (via the DC VGA box).  There is no way to turn them off unless there is an option inside the game (inside the software).

So, basically there isn't anything you can do to make these games look any better unless there is an option inside the game/software options menu.  And even then, if the game allows you to "turn on/off scanlines", its not really affecting your display, but rather making the scanlines less noticable (at the cost of maybe slowing things down or making it look more pixelated/blocky).

Hope this makes sense.

giantgonzolez

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Re:Questions on Dreamcast video
« Reply #2 on: August 04, 2003, 04:23:01 am »
You should also ask this question at this forum, since they specialize in exactly the kind of stuff you're talking about.
http://atarilabs.com/cgi-bin/UltraBoard/UltraBoard.cgi?action=Headlines&BID=11&SID=30
BTW, I always thought that when Dreamcast was displaying 15khz RGB it was always interlaced, and when it was displying 31khz vga it was always NONinterlaced/progressive scan.
Also, here are the  pinouts and stuff for the dreamcast,
http://www.gamesx.com/avpinouts/dricas.htm
Also, some Dreamcast games just don't support noninterlaced scan/progressive scan.


I'm using a PAL Dreamcast on a Scart TV with a real RGB cable and I have a few doubts about some issues regarding my console. I'm asking here becasue I'm sure there are people in this forum with enough knowledge and experience to answer these questions.

When I'm using my DC on my PC monitor via VGABOX, my console is displaying 640x480 at 31khz (as indicated in the OSD of my monitor). Correct? Now, I guess this is the same frequency used in Naomi cabinets, which have Arcade mointors capable of accepting video at 31khz, right? In fact, if you stare at those monitors you cannot see scanlines, as you cannot see them in a PC monitor. I suppose the picture in those Arcade monitors is non-interlace, right? But when I use my DC on the TV with the RGB cable, the picture is interlace. I guess it's interlace because a TV cannot accept 640x480 non-interlaced, am I wrong? I also assume the signal is sent to the TV at 15khz, correct? The interesting issue is that some low res games such as Last Blade 2 or SFIII double impact display non-interlace picture (more stable display and perfectly visible quiet scanlines). Would it be possible to have this non-interlace display with 640x480 games? And why other games such as SFIII third strike, which is also low res, display interlaced picture (no quiet scanlines). Could I change it to non-interlace with some hacking to my RGB cable?

And that's all. All I'd like to know is whether I can have 15khz non-interlace display in all Dreamcast games, be it on a Scart TV or an Arcade monitor, and what do I have to do to achive this. Or at least, if anyone knows how to display the incredible SFIII third strike with the same beautiful scanlines that happen with SFIII double impact. The picture of the Dreamcast with the RGB cable is superb, but it could be even better at 15khz non-interlaced. I guess it must be possible, because otherwise, how to users of low res Arcade monitors use their Dreamcast in their cabinets? If there's any DC user who has build a cabinet with this console, please let me know what you had to do for using it with your monitor, and what kind of picture you obtain in your Arcade monitor (interlace or non-interlace).

Thank you very much.
« Last Edit: August 04, 2003, 04:30:14 am by giantgonzolez »

b3atmania

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Re:Questions on Dreamcast video
« Reply #3 on: August 04, 2003, 08:28:57 am »

Using SCART (RGB) you always get an interlaced picture. There's no way around this I'm affraid.

Some high-end European TV sets can handle non-interlaced signals. These have either component (separate Y/Cb/Cy signals) or VGA inputs. These are also common on projection equipment.

Disregard the HDTV remarks by Dave K. as HDTV is non-existant in Europe.

Stormdemon

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Re:Questions on Dreamcast video
« Reply #4 on: August 04, 2003, 04:22:27 pm »
Dave, I think you have not understand my questions and I must say I have to disagree with many of the things you are saying. I'm sure you can have non-interlaced display in a SCART TV or an Arcade monitor. In fact, the scanlines I'm talking about are not software simulated scanlines and actually happen when you have a non-interlaced display with low horizontal rates. See for instance the difference of the picture of Windows in an Arcade monitor at 640x288 (non-interlaced) and the same picture at 640x480 (interlaced). With the first resolution the picture is as stable as on a vga monitor. The same stability can be seen in MAME when you use lower res modes at 15khz. Then you can even notice scanlines, not only because of the 15khz but because the resolution is really low. When it comes to the Dreamcast, the point is that it seems that most games display interlaced, but a few display non-interlaced. I'm sure the scanlines in SFIII double impact are not simulated and I'm sure I have non-interlaced display with this game. Launch the game with a VGAbox and you will see no scanlines at all. Of course you can have non-interlaced display using scart, not only with DC but also with PC.

b3atmania

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Re:Questions on Dreamcast video
« Reply #5 on: August 05, 2003, 07:38:13 am »
When it comes to the Dreamcast, the point is that it seems that most games display interlaced, but a few display non-interlaced. I'm sure the scanlines in SFIII double impact are not simulated and I'm sure I have non-interlaced display with this game. Launch the game with a VGAbox and you will see no scanlines at all.
Correct. The game can "see" the VGA box attached and will display non-interlaced. Remove the VGA box and it will display interlaced.

Quote
Of course you can have non-interlaced display using scart, not only with DC but also with PC.
No, you really can't. Display using SCART is always interlaced.

Stormdemon

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Re:Questions on Dreamcast video
« Reply #6 on: August 05, 2003, 02:24:49 pm »
b3atmania, you are right as regards high res games. They'll display non-interlaced on a PC monitor via VGA-box, and interlaced on a SCART TV. However, you are wrong when you say that display using SCART is always interlaced. I can prove that the display I have in my SCART TV using my ArcadeVGA or using my Dreamcast with the games I mentioned is actually non-interlaced (in both cases using RGB cables).

Dave_K.

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Re:Questions on Dreamcast video
« Reply #7 on: August 05, 2003, 05:43:06 pm »
After much research on the topic, I believe I finally figured this out. I was wrong in my previous post (sorry).  I was getting confused with the NTSC standard (which is always interlaced).  

An arcade monitor (or a SCART TV which supports RGB input) can indeed display a 15khz non-interlaced signal.  Essentially what you would get at 15khz non-interlaced is roughly 320x240 (otherwise known as Standard Resolution in arcade monitor terms).  This is why the ArcadeVGA can support some DOS modes in non-interlaced format (its really at 320x240 or something similar).  But anything over that, must be interlaced.

Ok, now onto your original question.  Can you somehow tell the DC to always output in non-interlaced 15khz mode?  Unfortunally not.  Its completely up to the game/software if its going to render in 320x240 non-interlaced or 640x480 interlaced (while in 15khz RGB mode).  It would have been nice if Sega supported another grounding switch in the SCART/RGB cable to let the game know your preference for non-interlaced 15khz, but alas nothing is there.

So the best you could hope for is that the game supports non-interlaced (like Last Blade 2 does by default).  Some games for the PS2 (like VF4 and Tekken4) actually have this non-interlaced support in the game config menus.  Whats funny is they call this "hires mode" but all its really doing is switching between interlaced and non-interlaced.  So if you are viewing at 15khz, and turn on high res, you are really lowering the resolution to 320x240!  LOL!  But it looks rock solid!  Obviously if you used this same option and had the PS2 component cables plugged into a US HDTV, it would switch to 640x480 non-interlaced.

Well I believe this puts the topic to rest!

BombProofPlane

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Re:Questions on Dreamcast video
« Reply #8 on: August 19, 2003, 12:51:53 am »
um no the resolution doesn't cut in half the option your seeing are filters

it wouldn't look rock solid anyway since tvs will only display interlaced signals unless they are pal tvs connected by rgb or hdtvs and this still requires the input to be progressive

virtua fighter 4 doesn't support 480p