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Thread: C64 image quality

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    vB Guru AmiDev
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    Default C64 image quality

    What is the best option for C64 video output? Is it limited to composite?

    In a discussion I'm having elsewhere regarding the XRGB Mini someone can't get a clean image into the upscaler.

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    Amibayer! Bryce's Avatar
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    You can get an S-Video signal from the C64 which will be much sharper than a composite signal. This is the best you can get as there's no way of accessing the RGB signals on the C64.

    Bryce.
    Last edited by Bryce; 1st June 2017 at 11:30.

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    older C64s (with 5pin video/audio out) only do Composite, as well as the RF out of course, later ones (with 8pin out) also do Luma/Chroma (svideo equiv.)
    Last edited by SaviorX; 1st June 2017 at 11:54.
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    resistance is futile! Amibayer! roy_bates's Avatar
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    c64 has chroma lume signals as standard apart from one that had the 5 pin port already stated

    by the way,if you have the skill to do it remove the rf box and recap it, it might improve the picture ...seen lots like this
    i have got too much hardware,it would only hurt your eyes to look at it here

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    Amibayer! demolition's Avatar
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    Yes, S-video is the best you can get (requires a series resistance to convert Luma/Chroma to S-video since the voltage level needs to be reduced) but some fine tuning is needed to get the best picture quality. There is no optimal value for the series resistance which fits all C64s, so changing this can help a bit. Also installing a Luma fix like this one can give a little extra:
    http://www.amibay.com/showthread.php...-Commodore-C64

    No RGB signals exists inside the C64, but it should be possible to make a C64 Luma/Chroma to RGB converter and achieve almost noise-free picture quality due to the fact that the palette is small and cannot be changed, thus all noise could be eliminated in the A/D conversion. I am looking forward to someone making this product so I can use my 64s with my OSSC.
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    Quote Originally Posted by demolition View Post
    No RGB signals exists inside the C64, but it should be possible to make a C64 Luma/Chroma to RGB converter and achieve almost noise-free picture quality due to the fact that the palette is small and cannot be changed, thus all noise could be eliminated in the A/D conversion. I am looking forward to someone making this product so I can use my 64s with my OSSC.
    S-Video to RGB conversion would not only be extremely complicated, but also, the picture quality could never be better than the source, so you may end up with an RGB signal, but it would be at S-Video quality, so basicaly useless unless you need RGB for connection reasons.

    Bryce.

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    Amibayer! demolition's Avatar
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    Quote Originally Posted by Bryce View Post
    the picture quality could never be better than the source
    That is only true if you are using some generic S-video to RGB converter but if you make one specifically for the C64, you know the color palette in advance which makes it possible to apply a very effective noise reduction. It may still not be 100% identical to the output from an emulator (which would be the reference) but I imagine it could be close. The 'pixel clock' is also well-defined which again helps towards doing a good A/D conversion. The loose ends would be the color transitions between neighbouring pixels since they are not fully defined in the source signal (cannot always go fully from one color to another from one pixel to the next).

    When I talk RGB here, I actually think digital RGB since some digital processing is required here. Converting it back from digital to analog RGB seems a bit silly if you want to send it to an OSSC or XRGB afterwards. Then it makes more sense to output the video straight as a DVI or HDMI compatible 50 Hz signal.
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    Going to s-video from composite can make a big difference. These are my results:


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    Amibayer! Bryce's Avatar
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    Quote Originally Posted by demolition View Post
    Quote Originally Posted by Bryce View Post
    the picture quality could never be better than the source
    That is only true if you are using some generic S-video to RGB converter but if you make one specifically for the C64, you know the color palette in advance which makes it possible to apply a very effective noise reduction. It may still not be 100% identical to the output from an emulator (which would be the reference) but I imagine it could be close. The 'pixel clock' is also well-defined which again helps towards doing a good A/D conversion. The loose ends would be the color transitions between neighbouring pixels since they are not fully defined in the source signal (cannot always go fully from one color to another from one pixel to the next).

    When I talk RGB here, I actually think digital RGB since some digital processing is required here. Converting it back from digital to analog RGB seems a bit silly if you want to send it to an OSSC or XRGB afterwards. Then it makes more sense to output the video straight as a DVI or HDMI compatible 50 Hz signal.
    Nope. Digital processing would be massively complicated, cost a fortune and still could never create the original picture. Generic S-video conversion is already complicated because you are trying to split a mixed signal back into it's original discrete signals. This process would already add its own noise to the picture. The digital processing would then have to recognise the noise and know what should be there using averaging and previous frame comparison. This would cause single pixels to disappear and cause rough colour transistions and the final result would most likely look worse than a good S-video signal.

    Digital processing is good, but it's not magic, it can't know what isn't there (unless you happen to be a member of CSI or some other U.S. Cop TV show )

    Bryce.
    Last edited by Bryce; 1st June 2017 at 15:27.

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    resistance is futile! Amibayer! roy_bates's Avatar
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    Quote Originally Posted by ajk View Post
    Going to s-video from composite can make a big difference. These are my results:


    i havnt seen any c64 quite that bad on composite
    i have got too much hardware,it would only hurt your eyes to look at it here

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