MiST VGA upscaling experiments

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SuperBabyHix
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Re: MiST VGA upscaling experiments

Postby SuperBabyHix » Mon Feb 27, 2017 5:08 pm

Sorgelig wrote:SuperBabyHix,
It's true that many (if not all) cores output slightly out of TV standard freqs. Real PAL resolution is 312.5lines per field. I don't remember any core providing exactly 312.5lines(may be only Minimig - but i didn't check its code as it's too complicated). So if core provides only 312lines or even 320lines - the vertical frequency is already doesn't match to standard PAL. So, you will have stutter issue if you will output to PAL. I suggest to set scaler output to 60Hz(NTSC). Stutter will be less noticeable.


I will give that a shot. Thanks for the info.

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mambrino
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Re: MiST VGA upscaling experiments

Postby mambrino » Wed Mar 08, 2017 5:14 pm

Sorgelig wrote:LKV353 accepts scandoubled RGBHV (48Hz/50Hz) video through VGA input. Although sometimes it's not well centered.

But can you see the whole picture? I have the GBS8200 scandoubler and (at least in my TV) the image is shifted down aprox. 20-30px (plus border) and GBS8200 has no position adjustment for VGA input.

Thanks ;)

Sorgelig
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Re: MiST VGA upscaling experiments

Postby Sorgelig » Wed Mar 08, 2017 10:28 pm

Yes, i can see the whole pic. But i didn't test all cores. Only those on my repository.

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DrOG
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Re: MiST VGA upscaling experiments

Postby DrOG » Sun Sep 24, 2017 3:02 pm

Hi!

My cheap chinese upscaler arrived at friday, here are my first impressions, and some screenshots (taken from my Samsung LE40B650 TV's framebuffer using ScreenCap SamyGo application, as usually).

Didn't test all the cores so far, perhaps never will (there are more than 60 if we count the arcades also, and some of them has 6 video output modes: PAL and NTSC systems, all with VGA, SCART and Component).

If you are interested in something sepcific question not discussed below, I'll try it in 1-2 days and share my results in this topic, don't hesitate to ask!

First of all, it's not an "original" Gonbes product, it seems to be a GBS-8220 without the second VGA output. Perhaps it's a clone of a clone, but paying attention it's price (18$ with shipping), it was a bargain.

The panel says it's a "HC-V3.5", whatever it means.
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It came in an antistatic bag, with a power cable, and nothing more. It has a VGA and an YPbPr input, no SCART - but we don't need it! If you want to built a SCART female->VGA male adapter, you can solder one using the schematic as follows:

VGA_SCART_function
1-------15-------RED
2-------11------GREEN
3--------7-------BLUE
5-------17-------GND
6-------13------R GND
7--------9------G GND
8--------5------B GND
10------18-------GND
13------20-----C SYNC

Or if you want to use a sync separator/stripper (i.e. LM1881 IC), here is a decription how to do that:

http://www.theisozone.com/forum/viewtop ... 20&t=47226

For us, who use this with an FPGA (i.e. MiST), there's no reason to do so: we have a pure CSYNC in scandoubler disabled mode on VGA pin 13, so a regular VGA cable is fine for the job.

On the board the S (composite sync) and the HS (horizontal sync) pins are joint, I verified it with a multimeter.

You can cycle between RGBHV-RGBS-YPbPr pressing the 'left' button.

In the scaler's 'Picture' menu I didn't adjust the Brightness, Contrast, Saturation or the R, G, B potentiometers on the board. I adjusted the Geometry in RGBS mode, and the 'Sharpness' in case of RGBS and YPbPr input. On the TV I used the same setting for every input, and adjusted geometry to bring out the best possible result.

So here are my experiences:

1.) I used a noname MOLEX PSU, shipped with my Logilink USB to IDE/SATA adapter to feed the board.
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It was powerful enough, the panel says all voltages between 5-18V should be fine.

2.) The Menu's language was chinese by default, but it's not too difficult to change to english. You can adjust a couple of things, but not the geometry if you have an RGBHV or YPbPr input (only in case of RGBS signal is the 'Geometry' submenu active).
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I have chosen the 1024x768 resolution from the 'Display' submenu (it's still lower than the physical panel size of my LCD TV/monitors).

3.)/A.) The Atari ST core works in both RGBHV and RGBS mode using US TOS (NTSC standard), and in RGBHV mode with UK TOS (PAL standard).
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/B.) In RGBS and YPbPr mode you can set the 'Sharpness' parameter found in the 'Picture' submenu. In RGBHS mode this does not have any effect on the picture quality.
It's in the range of 0 to 10, I recommend to use a value near 3 (see 3.)/A.)).
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/C.) In PAL RGBS mode the picture is unusable, it scrolls, freezes or the result is a black screen:
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/D.) In 'Mono' mode the picture was corrupted also.
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4.) Most PAL cores' RGBHV video is distorted, and the bottom 20% of the picture is missing (compared to my TV's SCART input in scandoubler disabled mode).
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This is a big problem because in this mode the Geometry menu is unavailable.
Unfortunately in most cases the PAL RGBS mode is not a working solution either (see 3./C.)).

5.) In some cores' RGBS (scandoubler disabled) mode there's a glitch at the top of the screen (C64 PAL mode and NES (NTSC) core):
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6.) If the given core supports YPbPr out (see Amiga AGA/minimig), it's a good alternative, as the picture is usually not distorted, and the sharpness can be set manually.
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7.) The board's scaler gives a bit blurry, but much smoother and less distorted picture compared to my TV: looks like it uses a more sophisticated resize algorithm (i.e. bilinear filtering instead of nearest neighbor). See the MSX core:
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8.) If you find an input signal compatible with the upscaler, you can connect it's VGA output to the Mini VGA to HDMI converter, and use it via your TV's/Monitors HDMI input.
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9.) So far I didn't found any serious artifacts (waves or 'snow'), although tried only still images so far. Will test later the smoothness of scrolling and the latency during games.

10.) If you have a very non-standard core, the upscaler wont't work with it (tried i.e. the Bashkiria-2M beta from Gehstock, the result was black screen).

CONCLUSIONS:
1.) The efficiency of this scaler depends wholesale on the given core: If it's a PAL-only core without YPbPr output option, there's only a little chance that it will work.
2.) Compared to the low price, it can be a cost-effective solution.
3.) This device would be much more useful if the 'Geometry' option could be activated in RGBHV mode. Another solution would be the transplantation of Atari ST core's 'Video adjust' menu to the firmware, but I think it's not so easy.

To be continued (perhaps)...

Gábor


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