Author Topic: Converting 15kHz analog RGB to digital  (Read 35325 times)

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Offline Legion

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Converting 15kHz analog RGB to digital
« on: June 08, 2014, 01:49:38 pm »
I recently got my hands on a Sony PVM RGB monitor. It's made my old 240p game systems look fantastic. I'd like to capture the gameplay to my PC. I've found a number of devices that do this, but they always involve some kind of upscaling, filtering, conversion to some kind of broadcast standard, etc. which I don't want. So I've been thinking about making my own capture device.

What I'd want it to do is take in the 15kHz analog R, G, B, and composite sync signals, convert it to some kind of framebuffer (ie. Frame 0, Pixel (0,0), R_value, G_value, B_value, Pixel(0,1), R_value, G_value, B_value, etc) and write out that data to a file. I've found some ICs that kind of do part of the process from Analog Devices such as this: http://www.analog.com/en/analog-to-digital-converters/video-decoders/adv7800/products/product.html

But they always output to some kind of broadcast standard instead of just providing the raw RGB digital data. The other problem is the package these ICs come in. The one linked above is in a 176 pin LQFP package. Clearly not hand solderable, so I'm not sure how to prototype with it.

I was thinking of something along the lines of: analog RGB IN -> Framebuffer IC (ADV7800 or something like it) -> uC -> USB or SD Card.

So does anyone know of an IC that's closer to what I'm looking for? Also, how do you prototype with these things?
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #1 on: June 08, 2014, 09:32:14 pm »
http://www.analog.com/en/analog-to-digital-converters/video-decoders/products/index.html

But I'm not sure they will lock at only 15 KHz

Also since 640x480 runs the pixel clock at 25.175 MHz, where did you get the 15 KHz from? it should be closer to 1/4 of that.

Unless you are talking about the vertical refresh rate, but that will have all 320 pixels of the horizontal line per cycle.

Best candidate seems to be the ADV7181C

http://www.analog.com/en/analog-to-digital-converters/video-decoders/adv7181c/products/product.html

Although it might not lock to the 6.3 MHz required for 240p

"Line-Locked Output Clock. This pin is for the pixel data (the range is
12.825 MHz to 110 MHz)."

But I'm not sure the Sony monitor will lock to 320x240 you sure the signal is not VGA?
 

Offline Sebastian

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Re: Converting 15kHz analog RGB to digital
« Reply #2 on: June 08, 2014, 09:35:12 pm »
I can't help you with finding an IC but LQFP is definitely hand solderable. The only thing you should have is soldermask between the pads, otherwise it could be a bit harder but still not impossible.
Fix the IC on one corner and check if it is properly aligned, if it is, fix it one the opposite corner. Then put lots of flux on the pins and drag-solder them, preferably with a hollow tip. Done.
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #3 on: June 08, 2014, 10:17:59 pm »
Sorry to spam a link on my first comment here, but did you read about Micomsoft's (and Startech's) RGB capture cards?  There is a thread about them here.

Micomsoft has the SC-500N1 (PCI-E) and the XCAPTURE-1 (USB 3.0).
Startech has the PEXHDCAP (PCI-E).

Drivers for at least some models are interchangeable between manufacturers, I think.

Capture and playback on modern PCs is a tricky thing.  It might not matter if your ultimate goal is to digitally preserve of the RGBs waveforms - perhaps an oscilloscope capture would do the trick, or something like that (people here know about that stuff).

But for playback on a modern PC, you have to deal with a few fundamental differences between the technology types.  Resolution is a problem on fixed-resolution monitors (like LCDs), and if the goal is to have 1:1 pixel mapping, you lose the aspect ratio and create something that has little visual resemblance to the original signal.  Upscaling is necessary on such devices.  Even CRT monitors aren't likely to support arbitrarily-chosen resolutions made for consoles, and if they did, they probably wouldn't look right without tweaking the overscan settings.

Framerate is also an issue.  On LCDs, you can expect to enjoy tearing and other glitches, even with framerate conversion.  MultiSync CRTs won't even sync with the output of some RGB devices, like a standard Raiden II arcade board (though I haven't gone and tested all old consoles - standard NTSC framerate should work better here).

I realize that these things might not matter in the long run, if we can assume we get variable framerates and CRT-like monitors without native resolutions.  But in terms of preserving the look, 1:1 pixel mapping is not a great compromise.

I'm not so big on video encoding stuff, but most of the stuff I know of expects you to use some standard resolutions - old consoles are all over the place here, again.  On top of that, I think the most modern (efficient) codecs use 16x16 macroblocks, i.e., the resolution needs to be divisible by 16, not whatever funky resolution NEC or Nintendo came up with.  So you likely need to pad the frames slightly - unfortunately now it won't look right once you go back to an appropriate 4:3 source.  Upscaling to a standard resolution neatly avoids this potential pitfall.

@ miguelvp:  You're talking about RGBHV stuff; he's talking RGBs.  640x480 / 320x240 resolutions seem like standard PC resolutions - different from 480i RGB (which is where the 15KHz comes from - compare to other retrogaming standards of 24KHz - rare outside arcades and some Japanese computers - and 31KHz, seen in some progressive scan output consoles like the original Xbox) which determines horizontal resolution by a variety of pulses; actual horizontal (and vertical!) resolutions vary from device to device.  Never heard of 6.3MHz required for 240p; should be the standard 3.58MHz assuming NTSC timings.  It goes without saying the signal is not making use of the VGA adapter.

Hope that wraps it up:  Glad to be here, hope some of this is useful.
 

Offline AmmoJammo

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Re: Converting 15kHz analog RGB to digital
« Reply #4 on: June 08, 2014, 10:20:29 pm »
RGB to ypbpr, then a ypbpr capture device ;)

Now... I'm not sure how the capture devices will go with the resulting ypbpr signal, as not all TVs will support a signal like this either....

However, converting RGB to ypbpr doesn't require any scaling or processing, its just addition and subtraction of signals, so the resulting image is the same quality as rgb. ;)
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #5 on: June 08, 2014, 10:33:47 pm »
oh, 30Hz that makes sense.

So he will need some 3 channel ADC that can lock at 3.58MHz pixel clock.

I was just dividing the 640x480@60Hz pixel clock by 4 for the timing guestimate.

As an alternative you can get yourself a TV Superscan 2 (not sure if it will lock at those frequencies either) and hack it so you can access the freeze frame.

I have one laying around and just opened it up, it uses a philips TDA8707 Triple RGB 6-bit video analog-to-digital interface, for retro gaming 6 bits per color should be enough I would think:

But it seems no one carries that chip anymore.



 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #6 on: June 08, 2014, 10:45:38 pm »
@ miguel:  Actually 59.94Hz, given that 240p allows each sweep to represent a full frame and not just interlaced fields.  But this is if you're only dealing with typical consoles - as noted earlier, there's devices giving RGB outputs for which references to NTSC or other standards don't make sense.

@ ammojammo:  I think just going with the Startech will be cheaper, unless you are OK with a real cheap YPbPr device with probably lousy drivers, and you are okay with a really cheap RGBs -> YPbPr transcoder, or you get lucky and score a Kramer multicoder / universal transcoder very cheaply.  I got a Kramer FC-4040 recently - gonna see how it performs - but it's really more than is necessary for just capture.  Still, the flexibility is good to have for using RGB devices on a YPbPr television.
« Last Edit: June 08, 2014, 10:47:57 pm by Ed Herdman »
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #7 on: June 08, 2014, 11:14:48 pm »
Now i'm confused, 320x240x60Hz = 4.608 MHz and that doesn't take care of the horizontal and vertical front and back porch, that's why I was guestimating the pixel clock to be around 6.3 MHz.

Nevermind I did find a source:
https://pineight.com/mw/index.php?title=Dot_clock_rates

BTW Ebay has the TDA8707  3 channel 6bit ADC chip from Hong Kong and China, go figure :)
datasheet:
http://pdf.datasheetcatalog.com/datasheet/philips/TDA8707H.pdf

Or you can get this http://www.ebay.com/itm/Advanced-Digital-Systems-ADS-Model-SFN-100-TV-SuperScan-2-Presentation-Module-/251476666889?pt=LH_DefaultDomain_0&hash=item3a8d2d6a09

Or bid on this:
http://www.ebay.com/itm/ADS-TV-Superscan-2-VGA-to-TV-converter-/321426344172

Not sure how much hacking you'll have to do to access the frame buffer after a capture. And if you want to capture actual video well this thing converts the vga to composite so it's streaming the data internally, it uses a Zilog z86c3012psc mcu but I bet the MCU doesn't play much part on the actual decoding/encoding

I'm attaching a picture of the TVSuperScan2 insides, maybe I can trace the digital outputs and see where they get buffered through.



Edit: Can't find the power supply :(
« Last Edit: June 08, 2014, 11:46:34 pm by miguelvp »
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #8 on: June 09, 2014, 12:48:26 am »
Miguel, I still am not sure if you understand that the OP's video source is not a PC VGA monitor.  It's 15KHz RGB, similar to 480i standard-definition television in the NTSC spec (you can have RGB for PAL televisions as well, of course, but few gamers care about this - I'm new here and Legion hasn't provided region details, though I note that the Micomsoft and Startech devices happily deal with multiple region formats).

re: the pixel clocks - I see where you're getting that number from, but consider that the actual systems the OP is going to be using have totally different resolutions, as you see in that list.  Not the PC ones - the ones like Super Nintendo and so on.  Here my knowledge is running out - I don't know if having 6.3MHz support is a matter of maximum bandwidth, with support for lower dot clocks, though I wouldn't make this assumption since compatibility in many areas is a minefield.

The ADS is just an upscaler - and probably not a very good one for gaming purposes, and totally useless if you can make use of software scaling anyway.  Likewise, composite capture is a waste of time when the OP has asked for preserving details.  Upscaling / framerate conversion aside, composite is just going to throw out most of those beautiful RGB details.

I don't have any familiarity with PC output scalers (the SuperScan 2 seems to have some scaling capability) but I expect they are lousy, all things considered.

If somebody did have a VGA capture card (and they were expensive when I checked a few years ago, though getting less so) then they could make use of a standard scaler to convert to 640x480.  Micomsoft stand-alone scaler boxes (like the XRGB-2 and the XRGB-3) do this quite well, though once again there is no sense in buying this equipment just for this use, when you can get better control and lower cost from just buying a USB 3.0 / PCI-E capture device which you can plug the source right into, and then do whatever you want with the resulting capture in software.
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #9 on: June 09, 2014, 01:09:03 am »
Yes the superscan has scalers (down-scaling mostly) to convert from PC to NTSC, but I was suggesting in hacking the device to take the analog to digital and the buffering parts of the board not to use the whole thing as a solution. SuperScan was made by Micomsoft btw (at least it has it embossed in the bottom of the case as the copyright holder), just older tech that might be able to deal with those lower frequencies.

As for the 15KHz RGB I get it, but he can't digitize a whole horizontal line at one time, he needs an ADC that is able to convert the signal at the pixel clock level, all three channels at the same time.

I think we need more info from the OP, we don't even know how many bits per color his system produces.
« Last Edit: June 09, 2014, 01:11:27 am by miguelvp »
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #10 on: June 09, 2014, 01:39:43 am »
Well, what are you aiming to provide?  I already gave the standard, affordable yet pretty much top-end choices in my first post, which supports everything without trouble.  These already contain all the components necessary to get the highest quality possible, including an appropriate ADC, without hacking.  The SuperScaler 2 is a single-purchase solution and cheaper than I thought - just not applicable for this question, especially if you lose RGB and have to go to composite.  (I also can't find any reference to Micomsoft having anything to do with the the SuperScan devices, which is surprising if it's true.)  If you want to offer a collection of parts in order to approximately build something, that's another matter, but probably more expensive and bothersome compared to getting something that's ready to go off the shelf.

This reminds me that I have an older RGB capture card for PCI (not PCI-Express) that I never used and need to get rid of.

I think the OP is going to be resistant to these choices out of the belief that 1:1 pixel mapping is desirable and natural (it really isn't).
« Last Edit: June 09, 2014, 01:42:02 am by Ed Herdman »
 

Offline Legion

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Re: Converting 15kHz analog RGB to digital
« Reply #11 on: June 09, 2014, 01:49:07 am »
Sorry to spam a link on my first comment here, but did you read about Micomsoft's (and Startech's) RGB capture cards?  There is a thread about them here.

Yes. I looked at those first. The problem is they are meant to take a signal from an old console and output it in a format compatible with a TV or monitor. But I don't need the signal output to anything, just recorded. The console connects to the Sony PVM RGB monitor which acts as a display, but the monitor also allows you to pass the signal on to some kind of capture device (I suppose originally some kind of DVCAM deck). I want the 1:1 mapping so I can save the frames as a series of images, maybe PNGs or something like that. Then I can import that into After Effects or Premiere Pro for editing and then output in something like H264.
 

Offline Legion

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Re: Converting 15kHz analog RGB to digital
« Reply #12 on: June 09, 2014, 01:52:15 am »
I think we need more info from the OP, we don't even know how many bits per color his system produces.

Since I want to use this with multiple consoles, I don't want to worry about the native bit depth of the console. I was hoping to convert each R, G and B pixel signal into an 8-bit value, so 24-bit color.
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #13 on: June 09, 2014, 02:07:23 am »
Are you sure you looked?  I didn't link the Micomsoft TV upscalers (XRGB 2, 2+, 3, Framemeister, and the lesser-known ones like the XPC-4 and the DISPL) but rather real RGB capture solutions.  Their primary purpose is not what you describe, which is more like the upscalers I've listed here.

As for what you're using this for - I thought so.  TBH, with 1:1 pixel mapping you're just competing with the emulator kiddies (been down that road a ways myself).  Again, capture only works if it's usable somehow - by capturing the signals you've already taken them out of their environment unless you have a way of feeding back the analog RGB signals to your PVM.  So it's just as well to consider putting it in a format that is presentable; otherwise it's a bear in the woods type scenario.  Even so, I think the Micomsoft / Startech capture devices should still give you some flexibility to capture in a smaller format.  (Upscaling will prevent the headache of trying to fiddle with resolution output, matching macroblock size if that's a problem, and framerate conversion might also be at issue; post-production packages are not going to solve these problems for distribution of the resulting video because you're still stuck with the applicable computer video formats in terms of framerate if not resolution.)

I just recalled another issue that is critically important:  Pixel transitions.  As miguelvp was hinting (I think) there isn't actually a solid, defined pixel, but rather a data burst with some fuzzy edges.  Trying to capture at exactly the internal resolution of the particular system (again, it's totally different from console to console) might not give you a well-defined pixel.  If you're going to capture from a Super Nintendo, say, you will find that the edges of an internally defined pixel (as you'd see from output in the Higan SNES emulator by byuu) aren't so sharply defined and may even bleed into each other, especially if you have one of the early revisions of SNES.  This is another reason why people often recommend going with a typical capture card, which does not give you a pixel-sharp output.

And yet another problem:  Many systems switch resolutions on the fly.  Square does this for some SNES games, switching from 480i to 240p.  Many other titles use 640x480-ish interlaced resolutions for title screens, menus, and inventory screens, but switch to something else for gameplay.

1:1 pixel mapping just doesn't exist anymore at the video output step.

I'd encourage you to post a question in that forum thread I linked - or I could do it if you wanted (edit: posted with a couple questions for clarification of my own).  Just to see if there is a way of getting what you want, and what's going to get most of the way there.
« Last Edit: June 09, 2014, 02:14:01 am by Ed Herdman »
 

Offline Legion

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Re: Converting 15kHz analog RGB to digital
« Reply #14 on: June 09, 2014, 02:44:09 am »
TBH, with 1:1 pixel mapping you're just competing with the emulator kiddies (been down that road a ways myself).

Yes, I've been thinking about that a lot. If picture fidelity is the highest priority then emulation is probably the best way to go since you eliminate A/D conversion and all the opportunities for noise and signal degradation on the analog side. But I also want to film people playing the games and their reactions to what's going on. Filming someone playing SMS on a PC is just... well, my nostalgic side just doesn't like it.

I spoke to Joe Redifer over at Game Sack about capturing RGB and he said:
Quote
That’s where it gets weird and expensive. I use a sync strike and a Micomsoft XPC-4 routed to a Blackmagic Intensity Thunderbolt to capture RGB video. The XPC-4 had to be adjusted on a per-system basis and sometimes per game and it’s never 100% perfect. A Framemeister might work as well.

Kind of turned me off that type of capture method, but perhaps the XCapture-1 plus XSync-1 doesn't have these problems? I'll have to read more about it.

The idea of building my own capture device is a lot less appealing. I had no idea the 8 and 16-bit systems switched resolutions like that.
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #15 on: June 09, 2014, 02:58:42 am »
@Legion,

Do you have a scope that you could capture a screenshot of a single horizontal line out of that output connector?
what model of Sony PVM RGB  do you have?

Also the problem is that you can't really automatically capture the video no matter what, you need to know the pixel clock, the front porch time the back porch time, the sync time and then when it's done with all the lines there is also frame front and back porch



For example here are the timings of a VGA signal (640x480 @ 60Hz)
http://tinyvga.com/vga-timing/640x480@60Hz

At the vertical sync signal you have to wait the sync pulse time and the back porch time before digitizing, then you have to digitize each pixel at 39.721946375372393247269116186693 ns intervals (inverse of the pixel clock at 25.175 MHz) then wait for the front porch until you get the next vertical sync.

At the end of the frame you deal with the vertical timings pretty much allowing you time to construct your frame.

Another problem is that all of those old triple channel ADC chips are now obsolete :(

http://www.ti.com/lit/ds/symlink/ths8083.pdf

You might be able to do it with standard ADC chips with multiple channels but it's not going to be trivial if you want to support several clock frequencies. That's why it would be good to know if the model of your Sony PVM RGB and at least some of the consoles.
 

Offline Legion

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Re: Converting 15kHz analog RGB to digital
« Reply #16 on: June 09, 2014, 03:00:41 am »
I have one laying around and just opened it up, it uses a philips TDA8707 Triple RGB 6-bit video analog-to-digital interface, for retro gaming 6 bits per color should be enough I would think:

I'll order one off ebay. Should be interesting to mess around with at the least.
 

Offline Legion

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Re: Converting 15kHz analog RGB to digital
« Reply #17 on: June 09, 2014, 03:07:37 am »
@Legion,

Do you have a scope that you could capture a screenshot of a single horizontal line out of that output connector?
what model of Sony PVM RGB  do you have?

You might be able to do it with standard ADC chips with multiple channels but it's not going to be trivial if you want to support several clock frequencies. That's why it would be good to know if the model of your Sony PVM RGB and at least some of the consoles.

I do have a scope, Rigol DS2072A. I'll try taking a snapshot of the signal.
It's a Sony PVM-20L2.
Consoles are NES, SNES, N64, SMS, Genesis, Saturn, TG16 and PC Engine Duo.
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #18 on: June 09, 2014, 03:12:16 am »
AFAIK, Shmups' own upscaler guy (Fudoh) sold off a Blackmagic setup a couple years ago, and I think the reason was that it wasn't really flexible or intended for this kind of application.  The Micomsoft and Startech devices (not so sure about the Startech drivers) are, however.  There might be some slight issues with the Micomsoft drivers for the SC-500N1 on European computers, maybe - but I think both companies have been at work ironing out the bugs.

The good thing about doing the capture the Micomsoft way is that the output looks reasonably close to the original - right aspect ratio, probably many subtleties of the original output are preserved.

Nostalgia really shouldn't point you in the direction of the monolithic block pixels.  This isn't even like the old engineering adage ("price, performance, quality: pick two"); 1:1 sharp pixel mapping and scanlines are simply incompatible with each other.

We can always re-open this discussion if some CRT scanning-like technology (laser displays, maybe) hits the market, but until then, you have to choose :)

@ miguel:  Take care not to idealize the situation too much:  As I stated, even within single system lines there are real differences in where pixel transitions happen, depending on the revision of system used.
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #19 on: June 09, 2014, 03:36:40 am »
I have one laying around and just opened it up, it uses a philips TDA8707 Triple RGB 6-bit video analog-to-digital interface, for retro gaming 6 bits per color should be enough I would think:

I'll order one off ebay. Should be interesting to mess around with at the least.

Understand that this doesn't capture video but it will do the conversion internally, unless you are talking about ordering the TDA8707 chip and doing your own board :)

Quote
as for the I do have a scope, Rigol DS2072A. I'll try taking a snapshot of the signal.
It's a Sony PVM-20L2.
Consoles are NES, SNES, N64, SMS, Genesis, Saturn, TG16 and PC Engine Duo.

Note the video is 75 ohm terminated, you'll need a T and a 75 ohm terminator to make it happy. Also if the cable is just an RGB cable the Green carries the Sync signal, unless the connector has separate horizontal and vertical sync.

On old monitors that were black and white you would use the green BNC since it ws the one that carried the sync signal

BTW I've have hooked VGA BNC's directly to my DS2072 (no A) just reads the voltage higher but I can see the signals fine. Also I think I have at least a Genesis or a Saturn around. Found them but I only have composite out of the Saturn and RF out on the genesis, not sure how you are connecting them to your monitor.

Because if you are using composite and RF out the monitor won't convert that to RGB and make it available externally  (as far as I know)

 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #20 on: June 09, 2014, 03:46:05 am »
@ miguel:  Take care not to idealize the situation too much:  As I stated, even within single system lines there are real differences in where pixel transitions happen, depending on the revision of system used.

No worries, the OP wanted to capture the signal directly so that's why i'm focusing on the direct approach, but I think it's not a trivial task nor I'm suggesting it's trivial, capturing data at these speeds of 4-12MHz is not trivial.

As for the pixel transitions well they have to follow the clock for the display to display it, it's not like the console is going to change the gun deflection at particular pixels.
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #21 on: June 09, 2014, 04:01:38 am »
There's some strange properties of RGB (and other) outputs on this class of devices where pixels bloom or bleed outside their expected boundaries, but yes, the pixel clock should be relatively stable, I'd hope.

I'm not sure if the PVM's RGB passthrough will transcode something like Y/C or composite to RGB.  I could try it out, one of these days.  There are some people who might be able to make use of that, though I suspect it's rare.  Many good Y/C and composite monitors should have a comb filter (not sure about Sony's PVM line for security monitors, which are a far lower level of PVM than the L2 series) and many capture setups will just allow you to apply filters as a post-process step.

If somebody does need composite or Y/C to RGB transcoding, there are some inexpensive (sub-$50, US dollars) units by Kramer floating around secondhand.  Their more flexible transcoders including component to component transcoders (i.e., RGBs to YPbPr) also can do this, and they aren't necessarily expensive either.

However it goes without saying that dealing with Y/C or composite this loses all the quality of dealing with RGB.

Getting cables appropriate for RGB transmission is a somewhat tortured topic - the people building them assume SCART style connectors (21-pin) are generally a part of peoples' setups, but that just adds more chances for interference and you also have to watch out for pinout differences between the SCART style and JP-21 (Japanese).  Additionally, grounding and shielding are sources of trouble.  Still, now's as good a time as any to get them.  If you go with the eBay sellers, one says shielding doesn't make any difference, while the other gets it.  And then there's all those ancient branded RGB cables made by OEMs in the '90s - not worth buying unless you want museum pieces or to do some work fixing them up.
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #22 on: June 09, 2014, 04:11:50 am »
That's my take as well regarding RGB out, it's just a loop from RGB in.

So it might all be a moot point, I would rather just use a video capture card that is known to work like the link you provided but that's not what he was asking.

Myself I have a Hauppauge HD PVR 2 Gaming Edition that can capture HDMI and component and convert it to H.264 directly and with audio, but it won't work for those consoles I think.
 

Offline Ed Herdman

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Re: Converting 15kHz analog RGB to digital
« Reply #23 on: June 09, 2014, 04:27:42 am »
The talk about composite is even further away from what the OP asked about.  The Hauppauge is probably very nice, but certainly not applicable either, even if it does have some kind of component input.  Seems mostly HD focused.

Many of the old systems supply RGB as standard; all that's required is an appropriate cable.
Some can have known modifications that allow RGB output (N64, TurboGrafx/PC Engine).
From that list, only the original NES is limited to an A/V connection, though the attention being given to that system has seen it recently derive not only an RGB mod, but there's also another project working to implement the system over HDMI, which of course can provide pixels (at the likely cost of way more pixels being displayed than are needed for simple 1:1 pixel capture, but modern codecs should ameliorate this problem substantially; even 1080p content shouldn't take up much space).

The PVM should be able to pass through any of these signals.

And again, it's worth pressing back somewhat against the original request when certain aspects of it appear impossible - at best, it's worth questioning to ensure that all the major issues are known, given the limited potential benefits and many downsides.  Pixel clock shenanigans aside, you still likely have to deal with framerate conversion and multiple resolution support - all possible, but I don't see the point when you can just whack in a modern capture solution and let it do the hard work.

Edit:  Well, since I got a bit of pushback on this elsewhere (???) I want to point out that the key here is not that 1:1 pixel mapping is a bad thing in of itself - rather I fear that it misses the point that these signals must go through an analog-to-digital conversion to be captured.  Trying to arbitrarily determine the exact boundaries of a pixel, and define it as a monolithic block, may well sacrifice some desired details.
« Last Edit: June 09, 2014, 04:58:34 am by Ed Herdman »
 

Offline miguelvp

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Re: Converting 15kHz analog RGB to digital
« Reply #24 on: June 09, 2014, 05:04:48 am »
Composite came about because he mentioned the Saturn, and RF out because he mentioned the Genesis as two of the consoles and I happen to have both, I don't have any of his other consoles.

I also mentioned that my Hauppauge won't work with those consoles and agreed with you on getting one of those known capture cards that are known to work like in the link you provided.

But maybe he wants something better than OK. Surely is possible to get the real timings and hook the ADC to a BeMicro CV FPGA and write the video in the microSD. At 10MHz tops an mcu might be able to deal with it too. Although a class 10 microSD might fall short on capturing 340x240@60Hz  at 6 bits per color raw data (10,368,000 Bytes per second). But some can do 14.6MB/s so might be ok.

Having the sync timings pre-programmed so that he can change the capture configurations on the fly to match his hardware exactly is not trivial but not extremely difficult.

 


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