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 Post subject: Dreamcast jailbars on VGA
PostPosted: Fri Oct 04, 2019 9:05 pm 



Joined: 04 Oct 2019
Posts: 2
Hi everybody! Dreamcast fan here.
I'm currently using a cheap VGA cable on a AOC 24" VA LCD. This monitor has 2 hdmi ports and 1 VGA (that I'm using for the dreamcast)
After setting clock and phase in order to get the best image possible I can say I am ok with the image, but I'm still getting some vertical bars, only visible in dark backgrounds/colours.
I'm not able to solve this by changing any setting in the monitor.
I just hope that my beloved Dreamcast is not defective... What can cause this issue in your experience?
https://imgur.com/a/nXxh8vK

Not my image, but same issue


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 Post subject: Re: Dreamcast jailbars on VGA
PostPosted: Sun Oct 06, 2019 8:32 pm 


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Joined: 16 May 2008
Posts: 1774
Location: Denmark
What VGA solution are you using on your Dreamcast?

To me that looks like it could be moire-patterns rather than jailbars. Most displays have trouble displaying the Dreamcasts resolution properly, and this could be the cause. Do you by any chance have Guilty Gear X handy? The checkerboard pattern in the special guage will smear if the display is incapable of displaying the resolution properly, but should look sharp if this is jailbars.


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 Post subject: Re: Dreamcast jailbars on VGA
PostPosted: Sun Oct 06, 2019 9:07 pm 


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Joined: 06 Mar 2006
Posts: 11883
Location: Germany
indeed - most likely sampling artefacts. Does your monitor report the incoming resolution? If it says 640x480 and applies the sampling rate for that particular resolution you get artefacts like that. The blurry edges on the time stamp are a giveaway as well.


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 Post subject: Re: Dreamcast jailbars on VGA
PostPosted: Sun Oct 06, 2019 9:39 pm 



Joined: 04 Oct 2019
Posts: 2
I'm playing with a cheap ebay vga cable plugged into my lcd.
I've found the time to make some photos and upload them.

https://imgur.com/a/kj0CjSN

You can see in gdemu menu the typical Dreamcast dithering pattern, without any other particular artifacts. I've found the best timings to use by manually adjusting clock and phase, without letting the monitor to auto configure on the wrongly detected resolution (640x480).

The issue I'm trying to solve happens in dark backgrounds, look at the 2nd picture. There are some vertical lines clearly visible, not really noticeable while playing, but I've been able to spot them at first on solid dark backgrounds (like walls in 3d games).


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