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PostPosted: Fri Mar 22, 2013 4:10 am 
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theclaw wrote:
By any stretch, far better is possible than Sega Nomad! (to be fair as a non-technical user I don't know what approach it uses for Sonic 2 in 2-player mode)

Sonic 2 in 2-player mode use VDP interlaced mode, which is documented.


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PostPosted: Fri Mar 22, 2013 7:03 am 
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Then what does Nomad do with VDP interlaced mode?


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PostPosted: Fri Mar 22, 2013 7:34 am 
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The VDP is vanilla MD stuff, no modifications.

What happes is that nothing happens, the LCD controller that takes raw analog RGB + Csync does not support interlacing and new field goes on top of old like in non-interlaced scan. Result would be flickery but since the stock LCD is so slow all stuff blends together.

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PostPosted: Fri Mar 22, 2013 9:16 am 
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Speaking of side-by-side, how about a NES shown on a 13" TV versus a 20" versus a 27", with the pictures of each scaled so the tubes look the same size. That'd show how the effective scanline spacing increases the larger the TV (I know that it's somewhat unpleasant on my 27").


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PostPosted: Fri Mar 22, 2013 9:52 am 
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blargg wrote:
Speaking of side-by-side, how about a NES shown on a 13" TV versus a 20" versus a 27", with the pictures of each scaled so the tubes look the same size. That'd show how the effective scanline spacing increases the larger the TV (I know that it's somewhat unpleasant on my 27").

This can still depend on the television; My 27" CRT has the beam focused such that the scanlines for 240p content are not very strong.


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PostPosted: Fri Mar 22, 2013 10:03 am 
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I don't have any small TVs, all are 28" or bigger...

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PostPosted: Fri Mar 22, 2013 10:07 am 
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I just remembered that there are lots of CRT TVs in the house I'm in. Three 13", three 27", and a 32". Too bad I gave away a 20" recently. I'll have to connect a NES to them and take some photos.


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PostPosted: Fri Mar 22, 2013 10:18 am 
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Blargg, if it makes any differences, I understood what you were talking about, I just didn't have much to say. :P

This is actually interesting to think about; 2x bright means that the phosphors are being stimulated a lot more than a regular television signal, which is why the colors of an NES look so distinct and vibrant on a CRT. But, if you were somehow able to feed the NES's video signal into something that manually inserts its own interlacing v-sync signal, I'll bet that'll make the colors change slightly, even if it's displaying the same picture.


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PostPosted: Fri Mar 22, 2013 10:31 am 
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I just realized that this 2x brightness is a big reason they had that warning about playing it on projection TVs, since those internally have CRTs which already run at a really high brightness compared to normal CRTs. It wasn't just that games show static images (score, or entire screen for puzzle games), it's that they were drawing each scanline twice as many times per second as an interlaced signal.


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PostPosted: Sat Mar 23, 2013 12:05 am 
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blargg wrote:
I just realized that this 2x brightness is a big reason they had that warning about playing it on projection TVs, since those internally have CRTs which already run at a really high brightness compared to normal CRTs. It wasn't just that games show static images (score, or entire screen for puzzle games), it's that they were drawing each scanline twice as many times per second as an interlaced signal.

If you would like me to hook up my oscilliscope I can do so... this seems incredibly founded in speculation. The scanline is not being drawn twice as many times per second as an interlaced signal. It is drawing roughly the same amount of times as a SNES, Mega Drive, PC-Engine...

TmEE wrote:
I don't have any small TVs, all are 28" or bigger...

It's monochrome, but I have a small 12" Zenith monitor that takes a Y input (signal + sync); would it be useful to take pictures of it showing anything?
Image


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PostPosted: Sat Mar 23, 2013 6:06 am 
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monochrome does not count due to design, but i came rainbow seeing your pic :oops:


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PostPosted: Sat Mar 23, 2013 6:13 am 
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Going over same area on the phosphor does not really make it brighter in non-interlaced scan. Maximum intensity remains the same. By The time the next field comes the phosphors are dark. It takes less than quarter of the screen for phosphors to dim down completely. It is all down to presistance of vision.
The light curve the phosphors exhibit is completely logarithmic. Very short peak and a rapid decrease in brightness. This is the reason the image is not perceived as flickery when the brightness is turned down on a CRT, you stay more in the gradual part of the slope.

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PostPosted: Sat Mar 23, 2013 10:59 am 
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Maximum brightness, yes, but the perceived brightness should be higher because the RMS brightness is twice as much.

The absence of flicker has as much to do with ambient lighting levels as with shape of discharge: a very dim CRT (if you could see it at all) in a very bright room will flicker perceptably.

I also don't know whether the phosphors used in old CRT-based projectors are different (and so have a different half life) than those in forward-view sets; necessarily older sets made before P22's discovery did.


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PostPosted: Sat Mar 23, 2013 12:09 pm 
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Quote:
blargg wrote:
I just realized that this 2x brightness is a big reason they had that warning about playing it on projection TVs, since those internally have CRTs which already run at a really high brightness compared to normal CRTs. It wasn't just that games show static images (score, or entire screen for puzzle games), it's that they were drawing each scanline twice as many times per second as an interlaced signal.

If you would like me to hook up my oscilliscope I can do so... this seems incredibly founded in speculation. The scanline is not being drawn twice as many times per second as an interlaced signal. It is drawing roughly the same amount of times as a SNES, Mega Drive, PC-Engine...

I'm baffled by how hard this is to communicate. Here are two frames; the left half is progressive, the right half interlace. The scanlines are numbered.
Code:
  Frame 1:   Frame 2:
  prog int   prog int
1 ********   ****
2                ****
3 ********   ****
4                ****

In progressive, scanlines 1 is drawn twice, once in each frame. In interlace, scanline 1 is only drawn once during these two frames. Progressive draws the scanline twice as many times per second. Hence, more (twice?) burn-in per second as an interlaced static image, and only of every other scanline, leading to irregular aging.

TmEE wrote:
Going over same area on the phosphor does not really make it brighter in non-interlaced scan.

Please explain this picture (2x_bright.nes):
Attachment:
compare.JPG
compare.JPG [ 13.29 KiB | Viewed 1483 times ]

In it, the NES is illuminating every other line. On odd frames, every other 8-pixel column is shifted down one pixel. So in effect, you get a magnified comparison between progressive and interlace side-by-side. The appearance is of the stable lines being twice the brightness as the ones illuminated only once every other frame. At a distance, the whole screen looks like a solid shade, with no vertical columns visible. Since on average only half as many lines are composing every other column, they must be twice as bright or else the column wouldn't appear the same shade as the interlaced one.
Code:
  Even frames      Odd frames
1 **************** ********
2                          ********
3 **************** ********
4                          ********
Appearance
1 ********--------
2         --------
3 ********--------
4         --------


Attachments:
File comment: ROM that demonstrates progressive being twice brightness
2x_bright.nes [40.02 KiB]
Downloaded 65 times
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PostPosted: Sat Mar 23, 2013 1:35 pm 
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I only see this effect here when I considerably turn down brightness.

I would say it varies from TV to TV. Only other TV I have here is an LG 100Hz wonder that deinterlaces any input... digitally... with rather blurry result and input lag, making games hard to play.
EDIT: I tried it in 50Hz, and I see the effect at near normal brightness too. I still had to lower it a bit. It is said the TVs in EU have longer glow on the phosphors, and it is probably what is happening over here, that diminishes the effect (and which is why I said that it should not really make the image brighter...).

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