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PostPosted: Wed Oct 25, 2017 8:43 am 
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Having just received a working NES console I plugged it into an old LCD TV that I had around the place using the yellow composite lead and I wonder whether the video quality issues I noticed are typical of a NES, or whether there are issues to be solved.

Unfortunately the issues don't seem too apparent on the videos I shot with my phone, which is slightly frustrating because the video quality is obvious when seen first hand IMO.

For example, there appears to be significant blue colour bleed (see both videos - marble madness and turrican) in all games. It's particularly visible on the white text on the game menu screens and less noticeable in game. Colour bleed doesn't seem to affect other colours, only blue.

In turrican I notice that the left hand side of the screen shows a blue vertical bar - what causes that? It doesn't appear on other games I have, so I don't think it's an issue with the TV or cable. I haven't seen it on other youtube videos of turrican, so is it a fault with the cartridge? I just bought it, so if it's faulty I need to contact the seller asap.

Turrican also exhibits the blue colour bleed as seen in other games, so could be an issue with the cable? NES? TV? I don't think this happens with the SNES that I have - at least I have never noticed it, but perhaps I'll have to check it out tonight to confirm.

Also, the picture in Turrican is generally bad with distinct lack of clarity. See the score at the top right of the screen. Against the blue background it's particularly noticeable, although it seems fine against dark backgrounds. Again it's hard to see in the video I shot, but as the graphics move there is significant jagges and shimmering. Potentially those are a poor description but maybe you'll know what I mean from the videos. I don't have any way to capture video from the console other than a phone, so it's the best I could do I'm afraid.


https://www.youtube.com/watch?v=bENHQX9U57A



https://www.youtube.com/watch?v=nU9ay4Sj3hE


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PostPosted: Wed Oct 25, 2017 9:40 am 
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Looks like your nes is working completely fine.

The blue bar on the left is just an option games can turn on to blank the left side.
The blue color bleed is probably just your tv not handeling the nes' video very well.

Lcds in general tend to not interpret nes video very well. In particular they tend to interpret the 240p signal as 480i, which can explain some of the ugliness when things start moving.
Note that the nes video out is always a bit jaggy though even on a crt.


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PostPosted: Wed Oct 25, 2017 12:01 pm 
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Colour bleed like that with the NES is normal, I think. I don't know how much your camera and/or TV is emphasizing it but it is inherent in the signal. Example demonstration: https://forums.nesdev.com/viewtopic.php?f=2&t=15080

The bar on the left side of the screen is also a very normal thing, done intentionally by the game. Super Mario 3 will do it too, and countless others.


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PostPosted: Wed Oct 25, 2017 12:07 pm 
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Color bleed isn't usually just one color, though.

Even were this proper YIQ decoding of NTSC, it shouldn't be blue... (the lower bandwidth of Q should make things have green/purple fringes)


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PostPosted: Wed Oct 25, 2017 12:50 pm 
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Lol thanks. Now i search again i see other videos on YouTube showing the same blue bar!

I'll try anther tv and see how the colour bleed is on that or if it's more than one colour. The tv i used to test was a cheap one from 10 years ago.


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PostPosted: Wed Oct 25, 2017 1:36 pm 
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lidnariq wrote:
Color bleed isn't usually just one color, though.

Even were this proper YIQ decoding of NTSC, it shouldn't be blue... (the lower bandwidth of Q should make things have green/purple fringes)

In the video it might look like the source images are white pixels with blue fringes from the contrast, but the source pixels in both cases are blue. (At least... the game is producing blue pixels. Do they actually look white on the TV?)

I think you can see bleeding of other colours too if you look around in the video (especially red).

Maybe in the video the bleed colour itself appears a little strange, but the shape of the artifacts look like the normal 3-pixel diagonal patterns you'd see?


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PostPosted: Thu Oct 26, 2017 2:29 am 
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Like other people said, these video artifacts are completely normal, and it's the reason why composite video sucks.

If you care about getting decent video quality out of an NES, I'd recommend looking into viletim's NESRGB boards:
https://etim.net.au/nesrgb/
The mod requires quite a bit of soldering (and desoldering!) skills, but if you aren't familiar with it, maybe you can get someone to help you.


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PostPosted: Thu Oct 26, 2017 4:03 am 
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So I tried it on our main TV this morning using the same yellow connector and the picture appeared better IMO. Blue colour bleeding was not apparent, so I think it's safe to say that the ancient, cheapo TV I was trying in the garage impacted the visuals.

I do like the idea of the NESRGB and I have done plenty of electronics work in the past, but for me the cost is prohibitive. I'm not sure that the benefit is great enough to justify the cost, plus I kinda like this NES to stay original. I haven't even done the CIC. Maybe one day, but not this side of Xmas :-)


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PostPosted: Thu Oct 26, 2017 8:29 am 
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Yeah, you gotta be pretty invested in NES stuff to do it. And for development purposes it's probably good to have a genuine composite output, just so you're always aware of how other people will see your game.

That said, I think it's a great investment. I never use composite output for any of my consoles except the NES which pretty much forces it, as there is no native RGB output on it without an NESRGB, even via traditional mods (such as you'd do for the PC Engine). And going from any RGB supporting console to the NES's composite output you immediately notice a huge difference :)


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PostPosted: Thu Oct 26, 2017 9:50 am 
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Some second-generation platforms also generate the signal directly in the HLS/composite domain.

  • I've been told Atari 2600 uses a bank of analog phase delays, analogous to what the NES does.
  • Apple II uses 1 bit for each of the four phases (+I, +Q, -I, -Q).
  • Odyssey2 uses Intel 8244/8245, whose video generation methodology I haven't been able to determine.
  • Intellivision uses AY-3-8900 feeding an AY-3-8915 encoder, which is essentially a 20x4-entry palette ROM feeding a DAC, with voltages for each of the four phases. I guess this could be replaced in a similar manner to NESRGB, though without the need to interpose palette access.
  • ColecoVision uses TMS9928/9929, which produces S-Video.


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PostPosted: Thu Oct 26, 2017 12:55 pm 
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tepples wrote:
Odyssey2 uses Intel 8244/8245, whose video generation methodology I haven't been able to determine.
The 8244/8245 emits RGBI video.

A separate IC ("612160-1") is fed 3.579545MHz, and a 105°(??) delayed copy via an R-L-C.

Without any particularly good evidence, I'd guess the NTSC encoder is running a digital multiplexer fed by these two phases, effectively rotating between just three of the RGB inputs, and then that composite signal is combined with the Intensity, Composite Sync, and blanking inputs to generate the desired composite signal.


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