Author Topic: C64 / C128 Video on HDMI screen - improving image quality possible?  (Read 2572 times)

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Offline TinkeringSteve

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #25 on: December 29, 2020, 01:15:09 am »
Retrotink is NOT the best for C64! It and the clone I menioned have the "white stripe" problem!

CRT is just inacceptable bulk, and often already too dark (worn tube).
Not a real option for my taste.

As said, the "Mcbazel ODV" has a distinctly overall better image than all other tested, including the clone of retrotink.
Its only downside is that it does not up-scale, which is not relevant for my versatile monitor that can be set to scale but retain aspect ratio.
I got that one to be able to also play old 4:3 PC games, and I'd reckon that I'm not the only fancier of older games who has a monitor like that, so an up-scaling feature of a HDMI converter is kinda irrelevant.
The tip with TV's video inputs still perhaps helpful to others reading. I myself don't have a TV, and that's unlikely to change.

So that hyped Retrotink thing is not all that impressive. Especially not for the price.
« Last Edit: December 29, 2020, 01:18:53 am by TinkeringSteve »
 

Offline Bud

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #26 on: December 29, 2020, 01:38:23 am »
Lumafix and such are difficult to adjust because "they are holding it wrong", lol. They mix the inverse clock signal into the composite signal. But the thing is that the interference mostly comes from Chroma output of the VIC. I guess noone bothered checking Luma and Chroma signals with a spectrum analyzer.  I did, so there you have it. Some of the Lumafix variations do add a portion of the inverse clock to Chroma but they do it incorrectly , when mixing in to Chroma the added clock should Not be inversed.
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Offline JohnnyMalaria

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #27 on: December 29, 2020, 01:42:09 am »
You'll never get a modern display to give you the same experience as an interlaced SD CRT. Get a used studio monitor off eBay. I was going to junk mine until I saw I could get $500 for it.
 

Offline Alex Eisenhut

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #28 on: December 29, 2020, 04:07:06 am »
It really sucks and I spent a lot of time and energy and money on various "pro" and consumer scalers, and I agree with your assessment.

The only scaler I like is the Viewsonic VB50HRTV and its successors.

It seems to handle the crap C64 video just fine, albeit with all the flaws piped right through.

The "pro" scalers give you lots of control, but it turns out the controls are useless. I'd like to have complete control on how it digitizes the video but since they are professional units they assume perfect by-the-book video signals. So the controls are mostly for the output side. Not useful.

I also tried LCD TVs and it is also hit or miss. Only certain LCD TVs work.

I am sticking to my 1080 monitor. The 2002 is the same. I don't like the 1084 series as they are flakey and fail. The 1702/1701s are great but hard to find.

It's a shame that Commodore didn't try to address the very real noise problems with the VIC-II, for a flagship graphics and sound machine a very sloppy approach. Oh well.
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Offline TinkeringSteve

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #29 on: December 29, 2020, 09:31:00 am »
Quote
It's a shame that Commodore didn't try to address the very real noise problems with the VIC-II, for a flagship graphics and sound machine a very sloppy approach. Oh well.

Well it was all kinda rushed from that I remember.
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Online Bicurico

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #30 on: December 29, 2020, 10:52:17 am »
The sales numbers of the VIC-20 and C64 prove that the design was perfect...

Who would care 40 years ago if there would be display issues on flat screens by 2020.

The cheapest options - as I said before - are:

- The C64 Maxi
- Raspberry Pi 3 running BMC64
- Using a CRT TV
- Using a 1701/1702 or 108x monitor

Offline Alex Eisenhut

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #31 on: December 29, 2020, 02:57:58 pm »
The sales numbers of the VIC-20 and C64 prove that the design was perfect...

No, it means it was good enough. If the chips were perfect, why did Commodore spin so many revisions? They could have spent a bit of time cleaning up the noise too.

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Offline Rasz

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #32 on: December 29, 2020, 03:23:43 pm »
You'll never get a modern display to give you the same experience as an interlaced SD CRT

interlace is the key here for the 240p signal Im sure

. Get a used studio monitor off eBay. I was going to junk mine

so the CRT was soo good you wanted to throw it out

until I saw I could get $500 for it.

until someone told you its a veblen good
<taps on horehead>genius</>

The sales numbers of the VIC-20 and C64 prove that the design was perfect...

No, it means it was good enough. If the chips were perfect, why did Commodore spin so many revisions? They could have spent a bit of time cleaning up the noise too.

They did so many revisions because they only had inferior engineers left after usual Tramiel excess staff cleaning maneuver. He fired almost whole C64 team after product release - Bruce Crockett (manufacturing), Al Charpentier (VIC) and Robert Yannes (SID) went to start Ensoniq, company Creative had to buy to provide actually working DOS compatibility on PCI cards.
Commodore kept to this strategy even after Tramiel left, they similarly got rid of Amiga hardware team (Jay,RJ,Needle) resulting in shipping same chipsets for 7 years under different names. Whole 9 years of Amiga without HD floppy (required basic PLL update inside Paula).

I'd like to have complete control on how it digitizes the video but

no buts, I found the perfect solution, and its cheap too https://www.eevblog.com/forum/repair/convert-640x200-video-screen-to-640x480/msg3385758/#msg3385758

instead of digitizing video with ADC it uses comparators and tunes every single bit threshold individually, reconstructs digital signal perfectly. Specifically designed for 8 bit computers.
« Last Edit: December 29, 2020, 03:34:50 pm by Rasz »
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Offline Shadowfire

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #33 on: January 07, 2021, 05:03:19 pm »
Retrotink is NOT the best for C64! It and the clone I menioned have the "white stripe" problem!
What white line are you talking about?
Here's my C128 NTSC hooked up to a 720p flatscreen via HDMI and the retrotink.
Note: I had to crop the original image to get it under the 4000kb forum file limit.
For the life of me, I have no idea what you are talking about.  Even with this photo you can clearly see the jailbars on the blue background (its actually worse in real life than in this picture), but there is no white line anywhere.
Edit:  I looked at the pictures in the the threads that you linked earlier, and did the standard POKE53280,0/POKE53281,0 to get a black background like in those pics, and still no line on the edge of the display like in those threads.  I'm not sure what to say, maybe its your TV?  I'll dig out my PAL C-64 and check it out in a bit.
« Last Edit: January 07, 2021, 05:15:57 pm by Shadowfire »
 

Offline Shadowfire

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #34 on: January 07, 2021, 05:26:37 pm »
OK, I have done a little running of cables and made some findings.
This is the PAL C-64 (running on the only TV I have in the house that will actually show a PAL video signal) with the C-64 Video Enhancer.  There are moire patterns on this picture, but you don't see anything like that in person, its a pixel-perfect image.
[attach=1]
I then put the retrotink on the PAL 64 and fed it into the same TV.
[attach=2]
It seems that the Retrotink does indeed show a bright line on the left side of the display, but only if you use it with a PAL unit.
Edit: I would suggest contacting Mike Chi about this; however, this may be what the pal C-64 is actually putting out (in the old days with a TV this would be in the overscan area where you couldn't see it, similar to how the NES had a horrible edge when horizontal scrolling)
(confirmed by below post, seems to be a problem with the PAL VIC-II chips.  You don't remember it being there because it was offscreen on the TV/monitor you were using back then.  Another reason to go with the video enhancer.)

« Last Edit: January 07, 2021, 05:40:42 pm by Shadowfire »
 

Online Bicurico

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #35 on: January 07, 2021, 05:34:01 pm »
That line is a bug/feature of the VIC-II.

Code: [Select]
FWIW this is neither the color burst nor the sync signal. It is a bug/feature in the VIC chip that makes the first 1.5 or so pixels of every line white.

The color burst signal would be to the left of the white line, and is not usually visible. Color burst is some defined color at zero intensity - so on a TV this would show up as black. On a B/W monitor and composite input with horizontal position adjustment you can see this as a faint band on the left if you move the screen entirely to the right.

The sync signal is even further to the left, and is 'blacker than black', certainly not white.

Source: https://www.lemon64.com/forum/viewtopic.php?t=73229

Regards,
Vitor

Offline Rasz

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #36 on: January 08, 2021, 02:34:51 am »
OK, I have done a little running of cables and made some findings.
This is the PAL C-64 (running on the only TV I have in the house that will actually show a PAL video signal) with the C-64 Video Enhancer.

this guy https://github.com/c0pperdragon/C64-Video-Enhancement ? This is totally skipping VIC-2 output, only way to successfully remove jailbars
works great with RGBtoHDMI https://videogameperfection.com/forums/topic/hdmi-output-using-raspberry-pi-zero/

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Offline Shadowfire

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #37 on: January 08, 2021, 01:40:49 pm »
Yes, the C64VE is c0pperdragon's board.

The RGB2HDMI project is an RGB -> HDMI converter (just like it says) but it needs to be tuned to the clock frequency of the generating hardware to produce good results.  They are basically sampling the analog signal and it needs to sample near the center, not the edge, of a pixel.  This would probably work well* (I haven't used one but the theory seems to be sound) to convert the C64VE's output (which IIRC can be configured to output RGsB instead of YPbPr) to HDMI.
 

Offline Rasz

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #38 on: January 08, 2021, 02:29:55 pm »
Its sampling at ~96MHz, I say thats enough to catch perfect transitions :)

https://stardot.org.uk/forums/viewtopic.php?f=3&t=14430
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Online NANDBlog

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #39 on: January 08, 2021, 03:22:19 pm »
If it is really a clock signal going into the component video signal, there must be a way to remove it, the good old way. Analog filters. If you would filter all the signals that are faster than the component video, so 4-ish MHz, you should be able to get rid of those lines. All you need is 3 opamps, and some passive circuits.
 

Offline Bud

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #40 on: January 08, 2021, 05:56:15 pm »
That line is a bug/feature of the VIC-II.

Code: [Select]
FWIW this is neither the color burst nor the sync signal. It is a bug/feature in the VIC chip that makes the first 1.5 or so pixels of every line white.

The color burst signal would be to the left of the white line, and is not usually visible. Color burst is some defined color at zero intensity - so on a TV this would show up as black. On a B/W monitor and composite input with horizontal position adjustment you can see this as a faint band on the left if you move the screen entirely to the right.

The sync signal is even further to the left, and is 'blacker than black', certainly not white.

Source: https://www.lemon64.com/forum/viewtopic.php?t=73229

Regards,
Vitor

Right, it comes out of the VIC chip and can be clearly observed as a luminance spike on the oscilloscope at the beginning of an active line.
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Offline Shadowfire

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #41 on: January 14, 2021, 03:05:20 am »
My point is that the C-64 changes pixel colors with an 8mhz clock, and if the sampling clock isn't locked to it (even though it might be running 12x faster) you will have the oddball color change last 13 or 11 clock cycles.
 

Offline Rasz

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Re: C64 / C128 Video on HDMI screen - improving image quality possible?
« Reply #42 on: January 14, 2021, 03:51:40 am »
My point is that the C-64 changes pixel colors with an 8mhz clock, and if the sampling clock isn't locked to it (even though it might be running 12x faster) you will have the oddball color change last 13 or 11 clock cycles.

have you looked at the link? its training its sampling clock to the signal. Its even able to recover pixel perfect picture out of BBC micro, computer which varies its pixel clock depending on whats on the cpu bus.
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