50Hz Fullscreen Display

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50Hz Fullscreen Display

Postby SainT » Fri Dec 14, 2007 11:39 am

I've been trying to get a 50Hz display on my PC and have found a way. You'll need an nVIDIA graphics card and an LCD monitor. Add a custom display resolution using the nVIDIA control panel and set it up like this (with advanced options turned on):

Horizontal desktop pixels: 800
Vertical desktop pixels: 600
GDI Refresh rate: 50
Bits per pixel: 32

Timing standard: Manual
Desired refresh rate: 50
Horizontal front porch: 32
Vertical front porch: 1
Active horizontal pixels: 800
Active vertical lines: 600
Horizontal total: 1048
Vertical total: 628
Horizontal sync width: 128
Vertical sync width: 4
Horizontal sync polarity: +
Vertical sync polarity: +

Scaling type: Display (none)

You should then get a 50Hz display option in the current SainT. I found I had to delete my monitor drivers from the hardware device drivers section of the control panel for DirectX to pick this new mode up, so you may have to do that also.

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Postby alexh » Fri Dec 14, 2007 11:48 am

Cool, smooth scrolling ahoy.

Most cheap LCD monitors wont do 50Hz, they have a minimum vertical refresh of 56Hz :-(

If you are using a non-nvidia card, could you use PowerStrip to do the same thing?

http://www.entechtaiwan.com/util/ps.shtm

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Postby SainT » Fri Dec 14, 2007 11:57 am

Yeah, powerstrip does the same sorta thing, however the display mode doesnt seem to show up as a directx mode. It just overrides the current display mode (I think). Or that's been my experience anyway.

I've also just found out that the 50Hz mode I have working is interlaced, so it looks poo for fast scrolling stuff. I thought it looked weird.

Ah, well, back to the drawing board so to speak. Getting a PC setup to sync to 50Hz is a pain, and my LCD wont do 100Hz, so I'm a bit buggered. I'll try it on the 26" HDTV in a bit, that should support 50Hz through DirectX I would think.

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Postby SainT » Fri Dec 14, 2007 12:08 pm

Actually, I think it does work ok after all. I tried it in 56Hz and 60Hz and I got the same nastyness -- I think it's just the ghosting on my LCD.

So even if you have old cheap-o LCD monitors (like mine!) you might be alright.

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Postby ijor » Sat Dec 15, 2007 4:20 pm

I'm not sure I understand you are trying to do. Do you want to get 50 Hz on any monitor (CRT or LCD), or specifically with a LCD monitor?

For CRT, what's the point on using 50 Hz? Why not 100 Hz. 100 Hz is usually well supported by most monitors, adapters and drivers.

For LCD ... well, it's a bit of a lose fight. As Alex is saying, not every LCD monitor supports 50 Hz. And it's not just "cheapo" ones, very good and branded ones require a 56 Hz minimum.

Using custom display modes is a bit cumbersome. Be aware that Nvidia (currently) doesn't support custom modes under Vista. Also note that a monitor might "pretend" to support 50 Hz but it could internally convert it to the rate it actually needs.

And even if you can get 50 Hz, you still have an issue of scaling because LCD monitor have really a single fixed resolution. IMHO, LCD monitors are not for high quality vintage computers emulation.

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Postby unseenmenace » Sat Dec 15, 2007 7:55 pm

ijor wrote:IMHO, LCD monitors are not for high quality vintage computers emulation.

I completely agree but of course its nice to be able to have the option of both 50Hz and 100Hz to improve the odds of being able to get smooth emulation.
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Postby SainT » Sat Dec 15, 2007 9:27 pm

50Hz will always be better than 100Hz with frame skip as with 100Hz you get the frame displayed twice causing the image to look jumpy instead of smooth with scrolling images. This is also true of 100Hz TV's and standard TV signals, which IMO make scrolling images look poo. So that is the point for CRT's, but very very few sync down to 50Hz, so this is rather a mute point.

This is more aimed at LCD users, as many LCD's dont support high refresh rates (mine for one). However mine seems to have no problem with 50Hz (despite what standards might say), apart from high image persistence. So this information will help those in this situation to get a far more acceptable image quality from SainT.

Some monitors may not work with this, however some will. So try it and see. As for CRT's being the only way to get the authentic look, then I would suggest just connecting up an old TV to the composite out on your video card and you're done. However may people dont have the space or inclination to do this, so just getting your LCD to sync to 50Hz is a great alternative! :wink:

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Postby Desty » Sat Dec 15, 2007 11:09 pm

Why would displaying each frame twice at 100hz look jumpy? Surely if it's the same frame, it would look the same as 50hz, unless there's some flicker drawing the frame twice?
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Postby ijor » Sun Dec 16, 2007 1:30 am

SainT wrote:50Hz will always be better than 100Hz with frame skip as with 100Hz you get the frame displayed twice causing the image to look jumpy instead of smooth with scrolling images.


I agree with Desty. I'm not sure I understand why it would look jumpy at 100 Hz. An animation being smooth or jerky doesn't depend on the frame rate. It depends on the relation between movement and absolute time. The number of frames per animation step is not relevant.

E.g., if you run an animation designed for 60 Hz, it would look identical at 60 Hz, 120 Hz, or 180 Hz (or 600 Hz for that matter). Because the animation rate would always be 60 Hz and that's what matters. The human eye doesn't perceive frames ... well, except ...

Except that at very low refresh rates, such as 50 Hz, there is flickering. The flickering is not directly related to animation smoothness. It happens even if the image is fully static because it is an effect of the eletronic beam scanning.

But the flickering might have a perceived influence in the animation. The flickering would make the image to be perceived less sharp. This in turn might give a feeling of a less jumpy animation. It is a similar effect as when watching a low rez picture in a modern monitor. The image looks worse than in a TV or a classic old monitor, because the image is now so sharp that is looks blocky.

However, this shouldn't be too significant. Personally, 50 Hz animations displayed at 100 Hz don't look "jumpy" to me.

Note that LCD monitors don't produce flickering because they don't scan. So if it looks jumpy to you at 100 Hz on a CRT, it should looks as much jumpy with an LCD monitor at 50 Hz (except that the LCD resolution scaling might give a different feeling).

So that is the point for CRT's, but very very few sync down to 50Hz, so this is rather a mute point.


Hmm, are you sure? I think that CRT monitors supporting 50 Hz are much more common (or if you prefer, less uncommon) than LCD monitors with 50 Hz support. This is changing lately, so likely all LCD monitors would sync at 50Hz in the near future.

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Postby SainT » Sun Dec 16, 2007 11:33 am

My information is based on impirical observation. The image will look jumpy at 100Hz because the SAME IMAGE is scanned twice. If you dont believe me, try it out. Pop down to Dixons and have a look at a 100Hz TV next to a 50Hz one (if they still sell them?) and you'll see scrolling images (such as end credits, or the SKY News ticker) look noticably jumpy.

'tis a fact.

I do agree with the fact LCD's are poo for fast scrolling though. A 50Hz update or 100Hz on an LCD is irrelevant because, as you say, refresh is at a pixel level and it's the rate of change of the pixel colour which is the issue (and why higher refresh rates are not suppored). And, yes, even 100Hz dual scan on a CRT does look way better than LCD. No competition. :wink:

My whole point was, "if you have an LCD monitor this infromation may help you get a better picture". For some reason it's ended up being a debate on the merrits of CRT's over LCD's and the way the human brain percieves moving images.

ta,
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Postby ijor » Sun Dec 16, 2007 6:25 pm

SainT wrote:My information is based on impirical observation. The image will look jumpy at 100Hz because the SAME IMAGE is scanned twice. If you dont believe me, try it out. Pop down to Dixons and have a look at a 100Hz TV next to a 50Hz one (if they still sell them?) and you'll see scrolling images (such as end credits, or the SKY News ticker) look noticably jumpy.


You are comparing apples and oranges.

The display problem with 100Hz TV is related to de-interlacing, digital processing and in most cases, re-interlacing back again. Think about it, it simply can't be done perfect due to the interlacing. And a consumer TV is far from performing the conversion as good as possible.

It is a completely different situation than doubling the frame rate of a computer animation that is non-interlaced, and where the whole process is performed by the source (computer) and not by the TV/monitor.

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Postby SainT » Sun Dec 16, 2007 6:47 pm

100Hz TV's don't de and re interlace, they display the fields twice instead of once. A 25Hz PAL full-frame image consisting of two 50Hz fields would be displayed as "AB" whereas a 100Hz image would be displayed as "ABAB" or "AABB" where A and B are the two interlaced fields.

Either way I still maintain through the use of my eyes I can tell the difference, ergo there is one. :wink:

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Postby ppera » Sun Dec 16, 2007 6:59 pm

Yeah. Don't mix here interlaced TV displays.

However, I think that instead forcing 50Hz, we should go on more achievable 75Hz.
There is very few program which has real 50Hz framerate on Atari ST.
Actually I don't know any. Smooth game as Nebulus has exactly 25 fps.
Probably demo authors will not agree, and if main goal is good displaying of some fancy demos, don't read this further :)

Problem of 75Hz is that we need to sync. it with real frame content change in games. Maybe to check when is screen address changed? Then shift it 1-2 frames by need... Keeping sound in all that may be also hard task...
Too much work for few titles ... (?)

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Postby ppera » Sun Dec 16, 2007 7:04 pm

SainT wrote:100Hz TV's don't de and re interlace, they display the fields twice instead of once. A 25Hz PAL full-frame image consisting of two 50Hz fields would be displayed as "AB" whereas a 100Hz image would be displayed as "ABAB" or "AABB" where A and B are the two interlaced fields.


ABAB will spoil it badly - jerky movement as we go back in time B>A.
Only AABB is good.
Point of 100Hz is in reducing screen flash.

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Postby ijor » Sun Dec 16, 2007 7:44 pm

SainT wrote:100Hz TV's don't de and re interlace, they display the fields twice instead of once. A 25Hz PAL full-frame image consisting of two 50Hz fields would be displayed as "AB" whereas a 100Hz image would be displayed as "ABAB" or "AABB" where A and B are the two interlaced fields.


It might de-interlace or not. Either way it doesn't just display the fields twice. It performs filtering and motion compensation. Otherwise ABAB would look terrible (as Pera is saying, you are going back in time).

Either way I still maintain through the use of my eyes I can tell the difference, ergo there is one. :wink:


You can tell the difference between a 50Hz TV and a 100Hz one? Yes, of course.

Or you can tell the difference between a computer 50Hz animation displayed at 50Hz vs. 100 Hz? If you can, it is because of the flicker, not because of the same frame displayed twice.

Try watching a 60Hz animation at 60Hz and at 120Hz. Tell me if looks jumpy for you at 120Hz.

ppera wrote:ABAB will spoil it badly - jerky movement as we go back in time B>A. Only AABB is good.


Actually ABAB is much better because the picture is more stable and flicker is reduced even further. High quality sets use ABAB. But they don't just repeat the original fields. They process them, use interpolation and motion compensation, and create their own frames at the new rate (e.g.: the second A is not the same as the first A).

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Postby unseenmenace » Sun Dec 16, 2007 10:32 pm

I can only speak of my experience of using ST emulators on my CRT monitor but 50Hz stuff looks silky smooth at 100Hz for me :)
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Postby SainT » Sun Dec 16, 2007 10:39 pm

Ppera's point of getting video refresh to look smooth at, say, 75Hz, is what I'm concentrating on now.

The whole refresh rate issue is fairly specialist, to be honest. Most people just want to be able to pick up an emulator and play what they want looking as authentic as possible without any hassle. Which is what I am really concentrating on.

Keeping the sound in sync and so on should be ok as everything is still based around the ST's 50(ish)Hz refresh. The PC is just the "view" onto the emulated ST. Video frames will be an interpolation of what is happening.

It's all looking quite good. However, the only way for real purists will be to hook it up to a 50Hz CRT. :wink:

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Postby ijor » Tue Dec 18, 2007 6:07 pm

SainT wrote:Ppera's point of getting video refresh to look smooth at, say, 75Hz, is what I'm concentrating on now.

The whole refresh rate issue is fairly specialist, to be honest. Most people just want to be able to pick up an emulator and play what they want looking as authentic as possible without any hassle. Which is what I am really concentrating on.


Sound very nice. A different refresh rate will never produce exactly the same result. But with current CPU/GPU power is more than feasible to perform a very decent motion compensation/interpolation.

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Postby ppera » Tue Dec 18, 2007 6:29 pm

Much depends of how is animation made. If game has consistent screen update then it may be even perfect.
For instance if it has screen update at every 4 V-blanks (12.5 fps) it will result in displaying every anim. sequence 6 times by 75Hz refresh rate. What should be practically same as on TV.

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Postby ijor » Tue Dec 18, 2007 6:47 pm

ppera wrote:Much depends of how is animation made. If game has consistent screen update then it may be even perfect.
For instance if it has screen update at every 4 V-blanks (12.5 fps) it will result in displaying every anim. sequence 6 times by 75Hz refresh rate.


Of course. But this is not exactly what he is going to do (at least, as I understand). He is not going to use a fixed 75Hz (or whatever) refresh rate. He is going to adapt the output to whatever is possible in the current PC. Many LCD monitors are hardwired at 60Hz. So 75Hz might not be an option.

So the idea (again, as I understand), is to implement video processing for refresh rate adaptation. It is quite complex, but a modern PC can do it, and some (many?) cards can do that in hardware already.

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Postby SainT » Tue Dec 18, 2007 7:18 pm

Yep, I will try and adapt to whatever refresh the machine supports. There are currently preferred rates of 50Hz (1:1), 100Hz (2:1) and 75Hz (3:2) in that order.

Any other refresh rate is also possible, but you hit less keyframes, so the picture quality will not be as good. I will also support ST rendering at 60Hz refresh (ie. NTSC ST's), but this is less important than getting a good 50Hz emulation to me.

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Postby ppera » Wed Dec 19, 2007 2:26 pm

ijor wrote:..Many LCD monitors are hardwired at 60Hz. So 75Hz might not be an option.


I doubt it. My LCD does 60Hz only with DVI and 1280x1024. Lower resultions (perfectly good for Atari emul.) work with 75Hz too.

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Postby Marakatti » Thu Dec 20, 2007 9:11 am

My LCD is a cheapest widescreen ViewSonic I could find (around 200 euros here in Finland) and it supports 75Hz, native res 1440x900.

For me it easily comes to mind that more expensive screens does it too then...
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Postby ijor » Thu Dec 20, 2007 6:28 pm

ppera wrote:
ijor wrote:..Many LCD monitors are hardwired at 60Hz. So 75Hz might not be an option.

I doubt it. My LCD does 60Hz only with DVI and 1280x1024. Lower resultions (perfectly good for Atari emul.) work with 75Hz too.


Are you serious? Because your monitor supports 75Hz you conclude that everyone does? For starters, my monitor notebook's doesn't.

Also a monitor might accept a certain resolution and refresh rate but it might not actually use it internally. Actually, this is possibly the case of your monitor, because LCD monitors have a single native resolution. So the fact that your monitor accepts higher frequencies at lower resolutions only, might mean that is related to a max conversion rate.

This probably explains why notebook monitors are more limited. Not because the monitor is cheaper (my notebook is not a cheap notebook), but because it doesn't have a refresh rate conversion and resolution scaling.

This is even worse in older/cheaper monitors, where regardless of the accepted refresh rate, their response time is too slow for 75Hz.

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Postby ppera » Fri Dec 21, 2007 8:44 am

I would not mix here 'serious' monitors with some notebook displays ( :D ).

I did not concluded that every LCD has 75Hz. You concluded that "Many LCD monitors are hardwired at 60Hz". That 'hardwired' is ridiculous. Converting scan rate is too complicated. Much easier is to support 22% wide freq. range.
Scanrate conversion exists only in monitors with some video (50Hz) input (in crappy ones :-) ).

Then you mix native resolution with scan rate. My monitor works at 75Hz and 1280x1024 (ar any lower) from VGA input, but only with 60Hz via DVI (lower res. can have higher Hz on DVI). It sounds little weird, but shows that conversion rate is not issue. That 75Hz is real 75, believe me.
Probably they use some DVI mode with less pins, bits, and therefore is 60Hz limit on DVI in max. res. (there are sites with more details about).


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