Progressive scan on composite

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mariovisic
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Progressive scan on composite

Post by mariovisic » Sat Jun 24, 2017 8:10 pm

Hi all

I've been using my game boy zero for a few months now, it's amazing. One thing that bothered me though was that the composite output on the raspberri pi was interlaced, for such a small screen it's less noticable but still annoying, some games it's more obvious where text will shift up/down 1 pixel every frame and appear to shimmer, or a sprite will do the same. It can make playing the game boy for long periods of time straining.

The pi never used to be able to output a progressive signal over the composite output, but in March it received an update to allow it to work :) You can see the discussion about it at Github https://github.com/raspberrypi/firmware/issues/683

On a CRT display you would get a stable image and nice scanlines but on my LCD display it doesn't produce scanlines, it does however stabilise the image dramatically. No more shakey text and shimmering sprites.

Here's how you go about it. Firstly update your Pis firmware to the latest stable version by running

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sudo apt-get update; sudo apt-get dist-upgrade
. Once you're running the latest version you can add the following line to your /boot/config.txt:

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sdtv_mode=16

You can check its working by running:

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tvservice -s
. The output should look like:
state 0x40001 [NTSC 4:3], 720x480 @ 60.00Hz, progressive
Let me know how you go :)

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jostie94
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Re: Progressive scan on composite

Post by jostie94 » Tue Jun 27, 2017 6:46 pm

thanks for the tip! :P

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sdtv_mode=2
worked best for me.
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I found this page about video options in config.txt for more info :)
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redled
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Re: Progressive scan on composite

Post by redled » Mon Sep 11, 2017 9:25 pm

jostie94 wrote:
Tue Jun 27, 2017 6:46 pm

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sdtv_mode=2
worked best for me.
Worked better for me as well! Thanks for that.

Although I'm still not satisfied with the "static" and harshness of the refresh rate on this Version 8 screen...

codeman0624
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Re: Progressive scan on composite

Post by codeman0624 » Tue Sep 12, 2017 7:19 am

redled wrote:
Mon Sep 11, 2017 9:25 pm
Worked better for me as well! Thanks for that.

Although I'm still not satisfied with the "static" and harshness of the refresh rate on this Version 8 screen...
Can you maybe start a new question thread about this? It would be helpful to see detailed pictures of your driver board, and the connections from it back to the RPi. Would also be good to see pictures of the screen, and the static you're referring to.

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Robochris
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Re: Progressive scan on composite

Post by Robochris » Wed Sep 27, 2017 8:32 pm

This helped a ton on my build. Thanks guys!

mariovisic
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Re: Progressive scan on composite

Post by mariovisic » Sat Oct 07, 2017 8:31 pm

Setting

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sdtv_mode=2
will simply set the output to PAL interlaced. The reason why the menu may look a bit better is that PAL is a higher resolution (576 visible lines instead of 480 lines).

While the game menu will have more resolution; the games you're emulating will all be designed to run in NTSC (assuming they are NTSC roms). So extra resolution won't make your games look at any better; moving to a progressive image instead of an interlaced one will however make your games look better and stop flickering.

The reason why we prefer NTSC roms is that many games don't make use of all 576 lines in the PAL region, they simply draw blank borders on top/bottom of the image, NTSC also runs at 60hz rather than 50hz so gameplay is more fluid.

Hope that helps :)

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FlashyFrank
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Re: Progressive scan on composite

Post by FlashyFrank » Fri Feb 23, 2018 5:10 pm

When I add "sdtv_mode=16" to my config file it makes my screen scroll up in a repeating loop.

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tinkerBOY
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Re: Progressive scan on composite

Post by tinkerBOY » Fri Feb 23, 2018 9:18 pm

FlashyFrank wrote:
Fri Feb 23, 2018 5:10 pm
When I add "sdtv_mode=16" to my config file it makes my screen scroll up in a repeating loop.
I get the same result when I tested it on 2 different 3.5" screens.
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Re: Progressive scan on composite

Post by Helder » Sat Feb 24, 2018 12:42 pm

That's what happens when an NTSC 60Hz signal gets a PAL 50Hz signal. Incompatible frequency and video mode.
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Re: Progressive scan on composite

Post by FlashyFrank » Tue Mar 06, 2018 8:03 pm

Helder wrote:
Sat Feb 24, 2018 12:42 pm
That's what happens when an NTSC 60Hz signal gets a PAL 50Hz signal. Incompatible frequency and video mode.
So why is this working for others? Are they using PAL screens? How can I get this to work on my screen?

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