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Atari 2600 RGB mod


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#51 jarreboum OFFLINE  

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Posted Fri Aug 7, 2015 4:39 PM

It's not lossless. There is some theoretical colour degradation because we're dealing with analogue signals but it's literally imperceptible. And the colour separation is just as good, which is the main problem with Composite and Svideo and their bleeding pixels. I have a CRT that can accept both inputs and I've been able to compare Component and Scart on Gen 6 consoles and I found no differences with SD sources. Component allows for 480p though so it's better for these consoles. I don't use a transcoder because I don't have to, but if I were in the US this is what I would do.

 

Regardless of whether it's equally good or slightly less good than RGB, it's a massive improvement over Composite and SVideo.



#52 collinp OFFLINE  

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Posted Sat Aug 8, 2015 8:35 PM

I haven't used Tim's RGB to component converter, but it should only need to apply a conversion matrix to the signal. The result should be quite good. You will not be able to tell a difference between RGB and YUV.

 

Mathematically RGB to YUV and back to RGB is not a lossless transform. That's largely academic though. Our entire video system is built on YUV.  Blu-rays look pretty darn good and they start with a YUV encoding on disc and are likely transformed from YUV to RGB and back several times before the video is display as RGB on a modern HDTV. 

 

A couple caveats however :

 

1. Tim's component converter outputs 240p just like the RGB signal. Most modern digital TVs that accept SD only really know how to deal with 480i and 480p. Many won't show a 240p signal at all and those that do often mangle it. The OP was going to use a CRT so it's likely compatible with 240p but for anyone hoping this will let them hook up to their LCD or Plasma there is a good chance it won't work.

 

2. There are two different YPbPr to RGB transforms. One for SD (Rec 601) and one for HD (Rec 709). Unlike RGB this leads to an opportunity for the source or display side to use mismatched transforms. When the transforms are mismatched the signal can be noticeably inferior to RGB. A correctly implemented TV should detect the signal type (SD or HD) and apply the appropriate transform. Unfortunately many HDTVs, particularly early models, get this wrong and apply just one of the transforms to all signal types. Some up-converting DVD players also got this wrong on the source side. The resulting picture when mismatched transforms are used looks mostly correct, but there are color shifts. Most noticeably green will either be too neon or too muted. If the OP's CRT TV is SD it almost certainly uses Rec 601 so there shouldn't be an issue.

 



#53 grips03 OFFLINE  

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Posted Sun Aug 9, 2015 5:18 PM

anyone install one of these yet?



#54 collinp OFFLINE  

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Posted Mon Aug 10, 2015 2:29 AM

anyone install one of these yet?

 

My guess is that unless you live next door to Tim nobody has one of these in hand yet.

 

Mine is apparently in the mail. I ordered the first day of availability and it shipped August 4th. I don't know when it will reach me in the US. 



#55 Grimakis OFFLINE  

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Posted Mon Aug 10, 2015 8:31 AM

It's not lossless. There is some theoretical colour degradation because we're dealing with analogue signals but it's literally imperceptible. And the colour separation is just as good, which is the main problem with Composite and Svideo and their bleeding pixels. I have a CRT that can accept both inputs and I've been able to compare Component and Scart on Gen 6 consoles and I found no differences with SD sources. Component allows for 480p though so it's better for these consoles. I don't use a transcoder because I don't have to, but if I were in the US this is what I would do.

 

Regardless of whether it's equally good or slightly less good than RGB, it's a massive improvement over Composite and SVideo.

 

 

I'm fairly certain that Component also uses Chroma Subsampling to allow for higher resolution signals. This would result in a lower color resolution that may or may not be perceptible to you.



#56 roland p OFFLINE  

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Posted Mon Aug 10, 2015 8:49 AM

I'm fairly certain that Component also uses Chroma Subsampling to allow for higher resolution signals. This would result in a lower color resolution that may or may not be perceptible to you.

I don't think this is applicable to this mod.
Read up here: https://en.wikipedia...oma_subsampling

Btw. there will be no noticable differences between rgb and component given the limited palette of the 2600.

#57 Grimakis OFFLINE  

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Posted Mon Aug 10, 2015 9:18 AM

I don't think this is applicable to this mod.
Read up here: https://en.wikipedia...oma_subsampling

Btw. there will be no noticable differences between rgb and component given the limited palette of the 2600.

Someone above was discussing what would occur if you transcoded component from the RGB signal produced from this mod. Chroma subsampling would take place when you go from RGB to YPrBR colorspace.



#58 collinp OFFLINE  

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Posted Wed Aug 12, 2015 3:51 AM

Someone above was discussing what would occur if you transcoded component from the RGB signal produced from this mod. Chroma subsampling would take place when you go from RGB to YPrBR colorspace.

 

 

True, most component signals are filtered to reduce chroma bandwidth. There's no interconnect reason for that however. The Pb and Pr cables are the same as the Y cable and full bandwidth chroma is legal in analog component video. Once you go to S-Video or composite then bandwidth reduction is necessary. 

 

From what I can see of the photos of Tim's circuit he's got a bunch of resistors presumably to do weighting and scaling of the RGB signals and dual Op Amps to do a subtraction for each chroma signal. He's got video driver caps on each signal and a single power smoothing cap. I don't see any low pass filters on Pb and Pr. I think they are likely full bandwidth. So it's really up to your TV. It may filter component at the input or it may not depending on how it's built.

 

However RGB is not immune to all this. The RGB signal is almost always converted to YPbPr and back even on analog sets. The YPbPr space is a much easier space for signal processing, especially in analog. If brightness, contrast, color and tint effect your RGB input your set has almost certainly converted to YPbPr for that processing. If your set chroma filters YPbPr it probably internally chroma filters the RGB to YPbPr conversion too.

 

Even if chroma filtering occurs you are unlikely to tell. DVDs and Blu-rays halve chroma horizontally and vertically and they look great. At most a low pass filter on component will halve the horizontal chroma but keep the full vertical chroma resolution.

 

Ultimately we're talking about an Atari here with 160x192 pixels and a 128 color palette. None of the subtleties of colorspace conversion or chroma filtering should be visible at all.


Edited by collinp, Wed Aug 12, 2015 3:55 AM.

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#59 Kosmic Stardust OFFLINE  

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Posted Wed Aug 12, 2015 4:49 AM

 

 

I'm fairly certain that Component also uses Chroma Subsampling to allow for higher resolution signals. This would result in a lower color resolution that may or may not be perceptible to you.

Chroma subsampling encodes the hue and saturation (or Pb and Pr) in chunks or 2x2 blocks while luminosity gets 1x1 samples. It's not that noticeable when combined with lossy compression algorithms. Wii-U Gamepad uses 4:2:0 encoding uncompressed at 854x480x60p to the Gamepad, and the 420 encoding is very noticeable when viewing colored text on web pages. Blue or red links are blurry mess while black on white is sharp and legible. You can also see sprite tearing when complementary colors intersect, for instance Mario's red hat on a green background in NSMB-U.

 

But while component video is more easily converted into 420 compared to RGB, and the Pr and Pb channels potentially contain less bandwidth on the assumption that they are differenced with luminosity, to say that component transmits less data than RGB would be a misnomer. They represent an equal amount of color space and there is a simple formula of differences and ratios to convert between the two.

 

Also I find it ironic that by design, NES and Atari cannot natively output RGB since the chips and color tables are encoded in Luma/Chroma. So breakout boards had to be fabricated for both consoles in order to fetch the logic states of the TIA or PPU. Shows how far the modding community has really come...  :D


Edited by stardust4ever, Wed Aug 12, 2015 4:54 AM.


#60 maiki OFFLINE  

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Posted Wed Aug 12, 2015 10:45 AM

Yep... really far...

 

I bet most people from US will not bother since RGB is sort of a luxury out there...



#61 jarreboum OFFLINE  

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Posted Wed Aug 12, 2015 11:24 AM

Yep... really far...

 

I bet most people from US will not bother since RGB is sort of a luxury out there...

 

They should. RGB, even when converted to Component, is a massive improvement over Composite and SVideo. Many of your later CRT TV sets had Component in with 480i, it's simply the second best (besides a professional display) to get the best looking picture if you're living in North America. It's also very cheap as everybody is discarding their old tubes.



#62 glazball OFFLINE  

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Posted Wed Aug 12, 2015 12:25 PM

Really looking forward to sending you my 2600 Yurkie.  You always do great work.  Keep us posted and put up some pics of a finished console asap!!



#63 CatPix OFFLINE  

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Posted Thu Aug 13, 2015 5:37 AM

Europeans don't need to import a console any more (except for the French and their shitty SECAM VCS).

I will try this when I'll eventually get this board on my 2600, but I think you're wrong.

As far as I worked that out, on French VCS, the TIA is a PAL TIA (same part number). From what I have seen, the color pin of the TIA just goes nowhere on the board, it is left unused.

The color generation seems to be made right before the RF signal is made, by an equivalent of a AY-3-8515 (a chip used in Pong system to generate 8 coulours of of the levels of grayscale generated by the Pong chips)

This would be confirmed by the fact that on French 2600, the Color/B&W switch goes into B&W mode for EVERY games - and games like Dark Chambers that use this switch to display a map doesn't display the map, showing that it's a totally independant process.

So as this mod use the TIA and CPU, it should work fine for SECAM 2600 as well.



#64 jarreboum OFFLINE  

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Posted Thu Aug 13, 2015 11:31 AM

You would have to restore the colour switch function. It seems easier said than done.

If you do manage it, please tell us and show how you did it!


Edited by jarreboum, Thu Aug 13, 2015 11:35 AM.


#65 spawnshop OFFLINE  

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Posted Sat Aug 15, 2015 5:18 PM

So, this may be a dumb question, but what is the difference between this and the smaller board mods that I see available elsewhere?    I understand the diffence with the remote jostick swtiches and the pallete options, but at it's core, the upgrades the RF to A/V out, correct?   (Or am i misunderstanding this?)

But this board seems very big and more difficult to install compared to the other like THIS.

 

Any help would be great.  I'm looking to upgrade my console, but in it's simplest form.   Although, i would rather support the members on this forum....



#66 Mitkraft OFFLINE  

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Posted Sat Aug 15, 2015 5:26 PM

This is an RGB output mod and I'm pretty sure it's the only one. Unless I am mistaken all the other mods are composite video or svideo. Generally speaking, the signal types from best to worst quality are RF (native kind used by the 2600), composite video, svideo, component video, RGB (also called RGBs, RGBHV and VGA[in a sense]), DVI, then HDMI. Check out http://retrorgb.comfor more info on RGB and its use with retro consoles in particular.

#67 netspecter OFFLINE  

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Posted Sat Aug 15, 2015 5:36 PM

Has anyone installed one yet?  Curious to see how well it works going through a xrgb-mini.  I've been checking the US order page daily hoping for the opportunity to order.



#68 spawnshop OFFLINE  

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Posted Sat Aug 15, 2015 5:59 PM

This is an RGB output mod and I'm pretty sure it's the only one. Unless I am mistaken all the other mods are composite video or svideo. Generally speaking, the signal types from best to worst quality are RF (native kind used by the 2600), composite video, svideo, component video, RGB (also called RGBs, RGBHV and VGA[in a sense]), DVI, then HDMI. Check out http://retrorgb.comfor more info on RGB and its use with retro consoles in particular.

 

 

Thanks.  I get it now  (duh....).    I think I will stick with an s-video or composite mod to start.

This looks very cool though!



#69 SpiceWare OFFLINE  

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Posted Sat Aug 15, 2015 7:03 PM

This is an RGB output mod and I'm pretty sure it's the only one. Unless I am mistaken all the other mods are composite video or svideo. Generally speaking, the signal types from best to worst quality are RF (native kind used by the 2600), composite video, svideo, component video, RGB (also called RGBs, RGBHV and VGA[in a sense]), DVI, then HDMI. Check out http://retrorgb.comfor more info on RGB and its use with retro consoles in particular.

 

You've got "best to worst" reversed, RF is the worst.



#70 Mitkraft OFFLINE  

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Posted Sat Aug 15, 2015 7:31 PM

HAHAHA!  Dyslexia skcus!

 

 

You've got "best to worst" reversed, RF is the worst.



#71 darcagn OFFLINE  

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Posted Sat Aug 15, 2015 8:15 PM

Has anyone installed one yet?  Curious to see how well it works going through a xrgb-mini.  I've been checking the US order page daily hoping for the opportunity to order.

 

Unfortunately everything has been delayed. I ordered in the first hour or so they were available (from the International order page), and my kit shipped, however, I was emailed a few days ago and asked not to install the board when I receive it because it has a software fault in it. He said that he will ship replacement boards out on Friday 8/14/15. 

 

I've already done all the case modification work, component relocation, wiring, etc. necessary for the mod, I'm just waiting for my shipment to get here so I can drop the board in the socket. I have an XRGB-mini and a capture card so when I get my stuff I'll post screenshots and video footage of the 2600 in 720p. 



#72 Mitkraft OFFLINE  

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Posted Sat Aug 15, 2015 8:37 PM

Can you capture in native resolution also?  I'm going to be running into an SD CRT and I'd love to see how pixel perfect it looks in native res.  Thanks!



#73 darcagn OFFLINE  

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Posted Sat Aug 15, 2015 10:33 PM



Can you capture in native resolution also?  I'm going to be running into an SD CRT and I'd love to see how pixel perfect it looks in native res.  Thanks!

 

 

Unfortunately my capture device doesn't capture RGB; I could use an analog converter to convert it to YPbPr and capture that way, but the capture card will treat it like a 480i source instead of having proper 240p support, and it won't look right. If I connect via XRGB-mini to go to HDMI, then the minimum resolution I can capture is upscaled to 480p. 

 

I can, however, hook it up to my 14" Sony BVM CRT monitor via BNC cables and take pictures of what it'll look like in RGB on an SD CRT. 

 

For those of you who aren't familiar with Tim's previous work the NESRGB, you can basically expect the output to look crystal clear and perfect just like an emulator would, but perform exactly like the original console does. As an example, here's a screenshot of Super Mario Bros. 3 via NESRGB upscaled to 720p with an XRGB-mini. 



#74 collinp OFFLINE  

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Posted Sat Aug 15, 2015 10:51 PM

Has anyone installed one yet?  Curious to see how well it works going through a xrgb-mini.  I've been checking the US order page daily hoping for the opportunity to order.

 

I don't think anyone's got one yet. They take forever to arrive from Australia to the US (2-4 weeks) and apparently there's been an issue and new shipments were sent on 8/14. Once the US distributor is up and running I would expect much faster delivery times. My NESRGB came from the US distributor and showed up in less than a week.

 

Tim has said this uses the same RGB output section as the NESRGB. The NESRGB works perfectly with the XRGB-mini I would expect the same here.



#75 collinp OFFLINE  

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Posted Sat Aug 15, 2015 11:55 PM

 

 

Thanks.  I get it now  (duh....).    I think I will stick with an s-video or composite mod to start.

This looks very cool though!

 

The 2600RGB can output s-video or composite as well as RGB. It can also do component with a small add-on board. I'd consider installing one of these even if I was only looking for s-video or composite. Most Atari video mods are dark and undersaturated. This page is quite old but it gives you a flavor for what you can expect from most mods http://www.cheeptech.../2600mods.shtml 

 

The 2600RGB on the other hand will regenerate much of the video signal from scratch and the result should be impressive. The NESRGB is a very similar design particularly in the output stages and it's s-video out is really, really good. RGB is better of course but s-video is closer than you might think. As darcagn said a few posts up about the RGB output "you can basically expect the output to look crystal clear and perfect just like an emulator would" With S-video it will be a little less clear with a little more color smearing, but overall a similar effect.

 

Also be aware that classic consoles output 240p even after video mods. Many modern TVs can't handle that signal despite having the right connectors. You may need some sort of converter box. A popular one is the xrgb-mini. It is nice though a bit pricey.






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