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Jamisonia
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Re: So.... Some SNESes output YPbPr.....

by Jamisonia Tue May 15, 2012 10:06 am

Read up on 240p signals for low definition TV LDTV. The FCC forbade anyone from broadcasting in it. Thats why nothing supports it these days. My understanding is even if upscalers accept it, none of them actually handle the signal properly. Only SD CRTs will handle the 240p signal correctly.
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Re: So.... Some SNESes output YPbPr.....

by Tildius Maximus Tue May 15, 2012 2:55 pm

I currently play my snes via component video on my plasma. I have an NTSC Scart cable that then goes to my Scart ---> Component converter and the component to my Plasma. The picture looks incredible, and the colors are bright and crisp. it's a mildly expensive setup, but I actually got the scart converter for my pc engine to play that via component as well, so at least i am using the box for more than one console ><
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Jamisonia
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Re: So.... Some SNESes output YPbPr.....

by Jamisonia Tue May 15, 2012 3:47 pm

We are all aware of the ability to convert RGB to component. However its often very expensive, and very confusing to get.
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Ziggy587
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Re: So.... Some SNESes output YPbPr.....

by Ziggy587 Tue May 15, 2012 8:14 pm

I showed Jeffro the results of my component output and he had some ideas for me. His opinion was that Y has to be amped, and the Pr and Pb lines were probably fine. So basically, the colors look washed out because the luma needs to be amped. He suggested to me to use a high speed op amp for it, or try a transistor.

The problem with using a transistor is that I'm not a video engineer so I'd only be able to guess using knowledge from other video mods I've seen. That and I don't have an oscilloscope or whatever, so I'd really only be guessing. I had the idea to use a transistor with potentiometers so that I could try and zero in on the range of resistor(s) I might need, but I'd still only be guessing.

So at least I have a few good ideas to try and play around with. :D
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Drakon
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Re: So.... Some SNESes output YPbPr.....

by Drakon Wed May 16, 2012 10:46 am

Please tell me this's a joke? Luma is brightness it has nothing to do with colours. Amping luma will make the colours appear even more washed out.

You can use pretty much any simple transistor video amp to amp luma. Colour amping is a bit more difficult to amp.

Here's a single transistor amp that should work fine with luma

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Don't build the sync circuit just the amp used on r / g / b they're all the same simple 1 transistor video amp.

Here's a more complicated 2 transistor amp that should work fine

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The single transistor one would be far less difficult to build.

But really this whole amping business is a pain for a video signal that's not such great quality. You might as well learn how to build a rgb to component video circuit if you're going to go through this much trouble.
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Re: So.... Some SNESes output YPbPr.....

by Ziggy587 Wed May 16, 2012 5:19 pm

Drakon wrote:Please tell me this's a joke? Luma is brightness it has nothing to do with colours. Amping luma will make the colours appear even more washed out.


Like I said, I'm not a video engineer, but I could see how luma might effect the colors. But yeah, the flip side might be true. Perhaps the luma is fine, but the two color channels need to be amped. Now that I'm thinking about it, that sounds more likely to me.

Thanks for the pictures, I might give the 1 transistor amp a shot.

Another idea I had was to take the YPrPb from the (re)inputs rather than from the outputs. I actually thought of this early on, but for whatever reason I put it in the back of my mind. The reason being is that the S-ENC outputs the YPrPb signals and passes them through a circuit before inputting them again, perhaps making the lines more TV-ready. It's worth a shot since it's so easy to just move the wires to different legs of the IC. I'm definitely gonna try it next time I mess around with that SNES. I'm thinking of moving the Pr and Pb lines and leaving the Y where it is and seeing how that looks first.
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Re: So.... Some SNESes output YPbPr.....

by theclaw Wed May 16, 2012 9:20 pm

Jamisonia wrote:Read up on 240p signals for low definition TV LDTV. The FCC forbade anyone from broadcasting in it. Thats why nothing supports it these days. My understanding is even if upscalers accept it, none of them actually handle the signal properly. Only SD CRTs will handle the 240p signal correctly.


It is that bad. Some TVs go a step further by outright REJECTING 240p over component input. Instead of corruption or artifacts, the worst affected sets just fail to process any video at all. Leading a "signal not found" type error message.
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Drakon
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Re: So.... Some SNESes output YPbPr.....

by Drakon Wed May 16, 2012 9:21 pm

Yeah I looked at my snes schematic of what's happening to those colour lines before they're re-inputted they're not going through amps they're actually being weakened. The luma line is shared with s-video so you could just grab the s-video luma from the solder spot of the multi av port and then you'll have it properly amped. That way you don't even have to bother building an amp for luma. But without a proper chroma amp or a decent encoder the colours will always look washed out.

Here let me suggest a much better idea. There's a reason I included the snes schematic in that zip... Here's the amp that the s-video chroma (colour) goes through before it goes to the multi av port

Image

Component chroma and s-video chroma are the same strength it's just s-video has all the chroma data combined into one line and component has the data split. So theoretically if you build two of these amps and add them to the component video colour lines you'll have perfectly amped colour strength with your component video.

And for anyone who's wondering I'm pretty sure the transistor in this amp is a 2sc2412

*edit* here I made a beginner friendly diagram

Image

I don't even think the 0.047 uf cap is polarized I just put the polarity to be safe.
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Jamisonia
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Re: So.... Some SNESes output YPbPr.....

by Jamisonia Thu May 17, 2012 10:47 am

This actually makes a lot of sense. Grabbing the Luma from the s-video is a good idea. It certainly wouldn't be complicated to build that amp for the chroma lines.
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Drakon
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Re: So.... Some SNESes output YPbPr.....

by Drakon Thu May 17, 2012 10:56 am

Jamisonia wrote:This actually makes a lot of sense. Grabbing the Luma from the s-video is a good idea. It certainly wouldn't be complicated to build that amp for the chroma lines.


Of course it makes sense component video is just s-video with separated colour data. The luma pin you're tapping for this component video mod is the same luma pin that s-video uses. And the s-video circuit already has an amp built into the pcb for the luma so just tap it at the multi av port after it passes through the onboard amp. If a colour amp would work on s-video I don't see why it wouldn't work on component video as well. I have no idea how well this amp works for increasing the colour strength though. I have no clue how weak the s-video colour is from the encoder used in this schematic. I took other amps that worked fine on the luma line and attached them to the chroma line of s-video and the colours didn't seem any stronger. You're welcome to build this schematic amp and see what happens since I've never tried it.
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