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Old 05 August 2019, 00:05   #1
John Man
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You can eliminate scanlines on the Amiga?

While doing a search on the internet for some technical details about another love I have (the zx spectrum ) I came across a comment someone posted which made me really curious:

"One interesting thing with the Amiga was there was a software hack you could use to eliminate the scan lines. I used to use a program that would force it to output non-interlaced workbench screens in interlace mode, only at the same resolution (640x200 or x256) with each line of the image repeated twice. This would get rid of the scan lines without adding any flicker since every two lines were the same, so there was no contrast change between them.mnem May 25 '17 at 17:49"


The original page can be found here:
https://retrocomputing.stackexchange...pectrum-screen

I am not sure what he means but is that even possible?
If so, could it be forced in games?
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Old 05 August 2019, 00:32   #2
ross
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Quote:
Originally Posted by John Man View Post
I am not sure what he means but is that even possible?
Yes, a normal interlaced setup where you reuse the same field in the other frame.
Quote:
If so, could it be forced in games?
Usually not, because you are forced to an incompatible 25/30Hz (PAL/NTSC) refresh.

In any case from what I remember from back in the days (with the CRTs) a little flicker is visible anyway, because between a frame and the next the phosphors turn off slowly,
it is only attenuated because the line immediately below is with the same signal.
The final effect is to have a less brilliant image, a bit flicky, but with almost invisible scanlines.
I don't think it's a mode that has any advantage ..
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Old 05 August 2019, 01:14   #3
Steve
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Maybe they are talking about MagicTV? It reduces the flickering effect in interlaced mode and is for AGA only Amigas. You can't use it for games though.

http://aminet.net/package/util/wb/magictv2
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Old 05 August 2019, 01:20   #4
John Man
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Quote:
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Maybe they are talking about MagicTV? It reduces the flickering effect in interlaced mode and is for AGA only Amigas. You can't use it for games though.

http://aminet.net/package/util/wb/magictv2

Possibly it is the software being referred to.
What a shame, I was hoping to be able to try it out on the A500.
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Old 05 August 2019, 01:54   #5
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Possibly it is the software being referred to.
What a shame, I was hoping to be able to try it out on the A500.
No, what it does is a completely different thing.
It attenuate flicker on native interlaced mode modifying the display data (and works only for WB compatible stuff..).
Nothing to do with scanlines.
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Old 05 August 2019, 09:04   #6
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Yes, it works only for applications for WB or with screen mode choice, but there is only a few classic games with Hi-Res screenmodes and another few with Hi-Res mode possibility. Most (if not almost all) games are in non-interlaced modes.

I suppose author of mentioned comment was talking about MagicTV utility.

There is also possibility that he meant about "double" modes (DblPAL and DblNTSC) or VGA-like modes (for ECS and AGA).
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Old 05 August 2019, 09:46   #7
John Man
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No, what it does is a completely different thing.
It attenuate flicker on native interlaced mode modifying the display data (and works only for WB compatible stuff..).
Nothing to do with scanlines.
Hum, in that case what could be the software the person was talking about?
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Old 05 August 2019, 09:51   #8
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Originally Posted by Solo Kazuki View Post
Yes, it works only for applications for WB or with screen mode choice, but there is only a few classic games with Hi-Res screenmodes and another few with Hi-Res mode possibility. Most (if not almost all) games are in non-interlaced modes.
If you don't mind me asking but what classic games work in Hi-Res or give the choice to switch to Hi-Res mode?
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Old 05 August 2019, 09:57   #9
Solo Kazuki
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This topic

and

This topic.

Last edited by Solo Kazuki; 05 August 2019 at 10:06.
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Old 05 August 2019, 10:51   #10
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Great!

Thank you!
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Old 05 August 2019, 11:17   #11
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Hum, in that case what could be the software the person was talking about?
The Lacer tool.

If I'm not mistaken it was introduced with WB2.0.
It force/toggles the display between interlaced and non-interlaced mode.
This is used primarily by allowing the Amiga to provide the signal required by genlock devices.

Commad line:
Lacer 0 (normal display)
Lacer 1 (double the field, 'fake' interlaced mode)

Last edited by ross; 05 August 2019 at 11:59. Reason: typo
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Old 05 August 2019, 11:29   #12
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If by dragging screens you have both interlaced and non interlaced in the same view, it will force the interlace on the whole so merely seeing the effect does not require any particular software.
And it flickers because even though the signal is the same for the repeated lines, it will differ every two lines.
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Old 05 August 2019, 11:31   #13
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When I wrote my first Amiga game, Brainbow, on AMOS, I decided to include a few lines of an interlaced mode at the top or at the bottom of the screen (I can't remember which), whilst the game screen itself was 32-colour lo-res non-interlaced. But because the interlaced mode was visible, the whole screen had the distinct flicker that comes from the Amiga, as I liked the look of it so much. I didn't do it again for my later Amiga games, however.

If you want to see it for yourself, Brainbow is surely available on ROM sites with ADF images, and the flicker should be visible on a real Amiga with CRT. Even so, under WinUAE, the interlace effect is visible, so it's the same thing.
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Old 05 August 2019, 11:56   #14
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Originally Posted by meynaf View Post
If by dragging screens you have both interlaced and non interlaced in the same view, it will force the interlace on the whole so merely seeing the effect does not require any particular software.

This is nothing special on Amiga and natively supported from the start.

What actually Lacer do is simpy change/toggle interlace in Graphics base (that change interlace bit in bplcon0) and RemakeDisplay with Intuition
(so the non-interlaced visible full-screen is now interlaced).
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Old 05 August 2019, 12:20   #15
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According this page Lacer utility is only for Genlock.

Quote:
Lacer (Classic Only)

The Lacer program only works when a genlock device is attached to your Amiga. It toggles the display between interlaced and non-interlaced mode. This is used primarily for video recording and genlocking by allowing the Amiga to provide the interlaced input required by video devices.

Last edited by Solo Kazuki; 05 August 2019 at 12:45.
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Old 05 August 2019, 13:12   #16
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Quote:
Originally Posted by Solo Kazuki View Post
According this page Lacer utility is only for Genlock.
And that page is partially wrong (or rather, incomplete).
You can try it yourself with the commands I wrote.

Using WinUAE:
- open a native 640x256 WB screen, use 'Scanlines' in Settings/Host/Display/Line mode
- toggle between Lacer 1/0
- enjoy the disappearance of the scanlines

Of course it's not visually the same effect you would have on real Amiga with a CRT.
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Old 05 August 2019, 15:56   #17
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There are several reasons why forcing interlace mode can be useful with modern hardware.

Many modern TVs are quite picky about input video signals, expecting them to be more or less standard-compliant, which non-interlaced video isn't. If you use an RGB-to-component converter to connect your Amiga to the component input, the picture might only show properly in interlaced mode. The same can apply to RGB-to-HDMI converters. Non-interlaced to interlaced transitions could mess up the display or cause the TV to blank the screen for a while.

Some video capture devices might only work with, or work better with, interlaced input. Since frame rate differs slightly between non-laced and laced modes, there could be issues with skipped or duplicated frames and audio getting out of sync.

For OS-legal programs you can use Lacer or SetLace. But for hardware-hitting programs like most games and demos you need to modify the program code. As a proof of concept, in this posting I attached an ADF containing two versions of the D.O.C. "Demons Are Forever" demo: the original and patched to force interlace mode.
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Old 05 August 2019, 18:04   #18
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I remember running my Amiga off various CRT TVs back in the day, and on non-interlaced screen modes, the screen would be steady as a rock, no flickering whatsoever.

Then, when I made a VHS recording off of my Amiga's output at around 1994, I discovered that the VHS tape also played back with rock-steady lines in the non-interlaced parts.

Finally, in early 2003-4 or so, I had the means of transferring the VHS tape to DVD via a DVD recorder that took VHS tapes, and immediately, I noticed upon both VHS playback and DVD playback, that this recorder had ADDED interlace to those formerly rock-steady parts. It made sense as I suppose, because of the stricter standards in more modern equipment, and I sometimes wondered if back then, changing the signal as the Amiga did would damage the CRT TVs I used it on. Apparently not, but finally, the interlace flicker was there throughout the Amiga DVD, no matter what the original screen mode was!
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