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Old 13 November 2016, 11:07   #1
jarp
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OSSC (Open Source Scan Converter) with an Amiga

Hi all!

I am a bit surprised that there's not much discussion about a OSSC (Open Source Scan Converter) in this forum - perhaps because it is not speicifically designed for the Amiga and it's external? Since I got my unit few days ago I decided to write few words about it. I think the OSSC resolves main problems with the Amiga's video output for many (judging from number of Amiga compatible monitor, scandoubler etc. related threads). So what is it? I'll quote XRGB wiki:

"Open Source Scan Converter is a low-latency video digitizer and scan converter board designed mainly for connecting retro video game consoles and home computers into modern displays. It converts analog RGB/component video into digital format, and doubles (or triples) scanlines of a single frame if necessary to generate a valid mode for digital TVs or monitors."

Most interesting features being (again from XRGB wiki):

* Linetriple-support for 240p/288p with 4 different sampling modes
* Very low latency (less than 2 input scanlines)
* Full-range 24-bit RGB output through DVI/HDMI

This is it:



I connected my Amiga 600 to the OSSC using a SCART lead (OSSC would take VGA also if you have VGA adapter for your amiga). BAM - it works out of the box! The OSSC has a lot of configuration options available but none of which needed to be tweaked. I know that some gaming consoles required fiddling around with settings but not Amiga it seems. However, after I used Overscan program to expand workbench screen to the max I had to adjust backporch settings a bit to get perfectly centered workbench. I also enabled linetriple mode. This is how it looks:





You'll immediatly notice that the picture is a bit small despite of linetriple mode. It is because my monitor is 27" 1440p monitor and sadly even linetriple mode is not enough. OSSC guys have promised 4x and 5x modes in the future which should address this issue also. And since it is open source, one could create custom firmware if they do not. Anyways most likely most of the people won't even have this problem because they either have full-hd displays or their displays can actually do scaling internally (mine cannot, which is a bit weird).

Some more pictures, I enabled funny background pattern to see how crisp the picture is:





Please notice that 99% of imperfections in the picture are actually due to my compact digital camera! None of there color bleeding problems are there and picture is perfectly crisp unlike in photos. There are SLIGHT imperfections in the picture (like vertical color banding) which tells that DA-AD conversion is there, but nothing which would bother me at all when actually using the Amiga:



Have to say that this is just perfect for me since VGA is not option for me at all (Indivision ECS, Jens, please do DVI version of it thanks). I can also connect other gear to the OSSC since it is not Amiga specific. Just perfect for me. I understand that many will prefer CRT but for me that's not an option because of many reasons, lack of space being one another being that 50Hz CRT triggers migraine for me (yes, my childhood was difficult beacuse of that ...

But there are problems also to be honest. The OSSC and/or my monitor has torubles syncing to any non-standard display mode. PAL works fine and while the OSSC seems to sync to NTSC mode without a problem but my monitor seems not to sync to NTSC. Any more exotic display mode wont work for me - no productivity, no Super72, nothing. Either the OSSC won't sync or my montitor won't sync or there are problems with picture quality. But PAL, it works without an problem and that's what I were looking for. Vampire 600 is there for anything else. Edit: The OSSC now synch to most of the modes when using VGA adapter.

Please notice that the OSSC won't do any frame buffering (that's why it is so good, no lag) so no scaling other than linedoubling/tripling/4x/5x... and no frame rate conversion which means that you monitor has to be able to sync to the modes also! But you just cannot get best of all worlds...

That's all I had to say about this unit...

-J

Edit: Here are pixel-perfect advanced timing settings for common Amiga modes. These settings will capture whole overscan area also. I did not include lineX3 mode settings because it's impossible to do in pixel perfect manner if correct aspect ratio is desired.

PAL:HiRes (724x284), PAL:LowRes (362x284):
240p/288p lineX3: Off
H. samplerate: 908
H. synclen: 60
H. active: 724
V. active: 284
H. backporch: 76
V. backporch: 25
Sampling phase: Adjust until you get stable and crisp picture.
Note: If V. active 284 does not work you may try 288 (PAL standard).

PAL:Super-HiRes (1440x283):
240p/288p lineX3: Off
H. samplerate: 1816
H. synclen: 72
H. active: 1440
V. active: 288
H. backporch: 198
V. backporch: 24
Sampling phase: Adjust until you get stable and crisp picture.
Note: Aspect ratio is wrong (correct one would require lineX4 support which is not there yet). But because of that mode is actually quite usable in Workbench if you have ultra widescreen monitor.

DBLPAL:High Res No Flicker (744x564), DBLPAL:Low Res No Flicker (372x564):
H. samplerate: 976
H. synclen: 96
H. active: 744
V. active: 564
H. backporch: 99
V. backporch: 10
Sampling phase: Adjust until you get stable and crisp picture.
Note: If V. active 564 does not work you may try 576 (PAL standard).

NTSC:HiRes (724x241), NTSC:LowRes (362X241):
240p/288p lineX3: Off
H. samplerate: 910
H. synclen: 60
H. active: 724
V. active: 241
H. backporch: 76
V. backporch: 16
Sampling phase: Adjust until you get stable and crisp picture.
Note: If V. active 241 does not work you may try 240 (NTSC standard).
Note: Sometimes the OSSC has troubles syncing into this mode, toggling power off and on may work.

DBLNTSC:High Res No Flicker (744X467), NTSCPAL:Low Res No Flicker (372X467):
240p/288p lineX3: Off
H. samplerate: 976
H. synclen: 20
H. active: 744
V. active: 467
H. backporch: 177
V. backporch: 74
Sampling phase: Adjust until you get stable and crisp picture.
Note: Aspect ratio is wrong (OSSC misdetects the resolution and force enables lineX2 mode). Mode may still actually be usable for Workbench use (if you have potrait monitor).
Note: Sometimes the OSSC has troubles syncing into this mode, toggling power off and on may work.

MULTISCAN:Productivity (680×495):
H. samplerate: 912
H. synclen: 96
H. active: 680
V. active: 495
H. backporch: 99
V. backporch: 12
Sampling phase: Adjust until you get stable and crisp picture.

HIGHGFX:Super-High Res (1024×384):
H. samplerate: 1304
H. synclen: 60
H. active: 1024
V. active: 384
H. backporch: 142
V. backporch: 9
Sampling phase: Adjust until you get stable and crisp picture.

HD720 (1280x360):
H. samplerate: 1576
H. synclen: 60
H. active: 1280
V. active: 360
H. backporch: 137
V. backporch: 9
Sampling phase: Adjust until you get stable and crisp picture.
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Last edited by jarp; 05 December 2016 at 23:42.
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Old 13 November 2016, 11:32   #2
Locutus
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That looks super nice, price is okay for a multipurpose scaler.

One thing puzzles me though, it says it does line doubling/tripling, but does that then mean you have a input\:\output pixel aspect ratio of 3\:\1 ?

Or does it buffer individual pixels and repeat those 3 times as well?
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Old 13 November 2016, 11:51   #3
jarp
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Quote:
Originally Posted by Locutus View Post
That looks super nice, price is okay for a multipurpose scaler.

One thing puzzles me though, it says it does line doubling/tripling, but does that then mean you have a input\:\output pixel aspect ratio of 3\:\1 ?

Or does it buffer individual pixels and repeat those 3 times as well?
Don't know the technical details but I assume it MUST do pixel buffering also in addition to line buffering because visible aspect ratio stays ok in both linedouble and linetriple modes. E.g. when my Amiga is in PAL mode and the OSSC is in linedouble mode my monitor reports resolution 720x576@50Hz and in linetriple mode it reports 1280x864@50Hz and aspect ratio is ok.

Also not sure if it adds any some blank pixels and lines at the beginning and at the end of the line and frame in order to end up with some sane resolution modern monitors would sync at.

Edit: Ahh, I am an idiot. Correct me if I am wrong but horizontal pixels needs not to be "buffered" at all since analog RGB signal does not have concept of pixel. Rows yes as each hsync pulse signals a new row and frames yes as each vsync pulse signals a new frame, but no pixels. It's just voltage of R, G and B components changing at a some rate picture source decides. When the rate is known (as is usually is), pixels can be extracted from the signal properly. How to double? Sample the voltage twice

Last edited by jarp; 16 November 2016 at 08:36.
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Old 13 November 2016, 16:51   #4
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Hold on, it just got better. I suspected that maybe my SCART lead does not offer perfect sync signal for the OSSC since some of the modes partially worked after I enabled aggressive sync LPF from the OSSC. SCART uses composite sync where both hsync and vsync signals are transmitted via the same conductor. Also my Amiga-SCART adapter uses resistor to approximately match TTL-level voltage of Amiga's composite sync to voltage expected by SCART.

So curious I was and I just soldered buffered VGA adapter for my Amiga where hsync vsync are transmitted separately and BOOM. The OSSC now syncs to every mode short of A2024 and Euro36. Also my monitor is able to sync every mode. Woohoo what a difference.

I don't have an oscilloscope at hand but I suspect that either Amiga's composite sync is dirty or resistor messes up voltages too much. VGA fixes everything.

Last edited by jarp; 16 November 2016 at 08:36.
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Old 13 November 2016, 17:38   #5
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I've been following this project quite closely but have yet to take the plunge. It's certainly cheaper than an xrgb mini but it's still quite an expensive bit of kit.
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Old 13 November 2016, 17:52   #6
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Looks cool.
But...
No price, no links.
After some search it seems like it's still unfinished and in "two more weeks" mode.
I can be wrong of course, but the situation is not exactly crystal clear.
And I would be interested in something like this.
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Old 13 November 2016, 17:55   #7
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You sign up for the news letter - waiting list, ordering details etc come through that:

https://www.videogameperfection.com/newsletter/

Here's the price:

https://www.videogameperfection.com/...rce-converter/

£152 without psu or remote.
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Old 13 November 2016, 18:00   #8
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Sorry, I didn't want to sound like I am marketing the thing so I left links out. I am not associated to the project at all in any case. But like trixster said, you can put your name to the waiting list at videogameperfection.com.

It's a homebrew project like Vampire and they are doing deliveries in batches. They order X units from the board manufacturer and when they arrive they start do deliver. You do not have to pay until your unit is ready. I got my unit few days ago from batch two. First batch was something like 200 units, second batch was 500 units and I assume third batch will be large enough to get everybody, who are on the waiting list their, an unit but do not take my word on it.

As far as I know, third batch should arrive for new year or something.

Last edited by jarp; 13 November 2016 at 18:06.
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Old 13 November 2016, 18:10   #9
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So it is finished in a sense that you can order an unit and use it when it arrives no problem. But it is also work in progress in a sense that new features are developed and compatibility is improved all the time.

It's a FPGA thing so users can just upgrade it whenever new version is released.
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Old 13 November 2016, 18:59   #10
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I have one of the first ones from Marqs himself, and it's wonderful. Well recommended if you can get your hands on one.
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Old 13 November 2016, 20:07   #11
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It really looks good! Although a bit pricey. I understand it is not possible to provide a quality product of this complexity for 10 bucks. It just means we need more time for scraping up the funds
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Old 13 November 2016, 20:25   #12
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Well, lag-wise it's much better than the XRGB/Framemeister mini and costs only the half of it. Interesting device, maybe next year.
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Old 13 November 2016, 22:59   #13
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Does it have scanlines emulation?
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Old 14 November 2016, 00:29   #14
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Yes, it does.

http://retrorgb.com/upscalercompare.html

[ Show youtube player ] (Looks great in 1080p fullscreen)

Last edited by Retro-Nerd; 14 November 2016 at 00:39.
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Old 14 November 2016, 07:58   #15
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Quote:
Originally Posted by jarp View Post
Don't know the technical details but I assume it MUST do pixel buffering also in addition to line buffering because visible aspect ratio stays ok in both linedouble and linetriple modes. E.g. when my Amiga is in PAL mode and the OSSC is in linedouble mode my monitor reports resolution 720x576@50Hz and in linetriple mode it reports 1280x864@50Hz and aspect ratio is ok.

Also not sure if it adds any some blank pixels and lines at the beginning and at the end of the line and frame in order to end up with some sane resolution modern monitors would sync at.
So correct Integer scaling, this would be perfect for my NeoGeo as well.....jummy.....must resist temptation...
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Old 14 November 2016, 08:10   #16
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Is there a Youtube clip demo'ing this product?
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Old 14 November 2016, 08:38   #17
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What kind of demo are you looking for? Junkerhq has a rundown of its settings and what they do, post 14 in this thread has some example output.

http://junkerhq.net/xrgb/index.php/OSSC
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Old 14 November 2016, 08:49   #18
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Here's plenty of games (non-Amiga) running thru OSSC:

[ Show youtube player ]

Then pretty nice review emphasing both pros and cons of the OSSC (starts at 18:20):

[ Show youtube player ]

Last edited by jarp; 14 November 2016 at 08:59.
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Old 14 November 2016, 09:19   #19
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Quote:
Originally Posted by jarp View Post
Here's plenty of games (non-Amiga) running thru OSSC:

[ Show youtube player ]
Demo of something like this but amiga related.
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Old 14 November 2016, 21:06   #20
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Unfortunately I have found none. I would shoot a video but I do not have any HDMI recording device at hand :/
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