What's your Workbench screen resolution?

[iljitsch]

The Workbench image with the scanlines is pretty good, but it there's a wave of non-uniformess over it.

I'm not sure I'm seeing that. Could you explain this?

The Workbench background with just the scanlines shows up a bit darker and then a bit lighter as you move from the top to the bottom.

Interger scaling makes the aspect wrong, however, and their scan line implementation is just the simple "make it darker" approach. If you don't have a 1600 NITS HDR monitor, it ends up being too dark, IMHO.

For PAL lores or hires/interlace the pixel aspect is 44:44 or 22:22, respectively, so there integer scaling has no aspect ratio issues.

For NTSC, the pixels aren't square so there integer scaling does indeed produce a different aspect ratio. Which is a problem for software that sticks to the guidelines, but there's also a lot of software that just assumes square pixels on NTSC... so hard to win that war. And indeed, non-integer scaling in the horizontal direction, especially in lores, is rarely a problem. Each lores pixel becomes four or five LCD screen pixels, and having some be four and others five is not enough of a difference on regular content. Not good for alternating black/white pixels, though. But that's more a 1980s Mac thing.

And yes, the image gets darker.

Interlacing needs to be fixed at the source, there is no acceptable way to deinterlace video after the fact -- they're all compromises.

Yes, interlace is annoying. I have been experimenting with non-interlaced 25 or 30 Hz screen resolutions because that way I can use 256 colors without the CPU losing its chip mem access 50% of the time. But that's also not great, with the mouse pointer becoming very jerky. Only real solution here would be an RTG graphics card, but I don't think that's in the cards for my A1200... (A3000 does have one, but then again only 8 MB fast RAM and a 25 MHz 68030, so hard to take advantage of all that interlace-free screen real estate.)

[fxgogo]

For PAL lores or hires/interlace the pixel aspect is 44:44 or 22:22, respectively, so there integer scaling has no aspect ratio issues.

So I would take both of those ratios as 1:1, but both analog and digital PAL signals do have a pixel aspect ratio that are not 1:1. Am I missing something here?

[nonarkitten]

For PAL lores or hires/interlace the pixel aspect is 44:44 or 22:22, respectively, so there integer scaling has no aspect ratio issues.

So I would take both of those ratios as 1:1, but both analog and digital PAL signals do have a pixel aspect ratio that are not 1:1. Am I missing something here?

The original Amiga hardware documentation states 44/52 for NTSC and 44/44 for PAL, which is factually and demonstratively wrong. In reality, PAL was between 1.041 and 1.067 (~1.05) pixels wide for each scanline and NTSC was 0.833 to 0.86 (~0.85) pixels wide per scanline.

So if we take a 640x400 NTSC image and integer scale it on the vertical to <= HD we get a multiple of two, or 1280x800. But that will look "too wide" so we need to squish it horizontally to about 1088x800. Note that 4K upscaling is a bit more precise since we can get 5 lines for a final res of 2720x2000. And 2720/2000 is very near 4:3.

And if we took a 640x512 PAL image, we get the same x2 on the vertical but now it's a bit wider at 1344x1024 and with 4K scaling we can get 2688x2048. Again, this ends up very close to 4:3.

From this point if the monitor then bilinear scales to full frame, it won't look too bad.

The fact that some games use round circles and some are oval comes from dealing with games that used the same artwork for both PAL and NTSC releases. It just wasn't worth their time fixing it.

To get 16:9 resolutions on NTSC you'd need 840x400 or in PAL, about 867x512, which would be a very cropped superhires.

[nonarkitten]

The Workbench background with just the scanlines shows up a bit darker and then a bit lighter as you move from the top to the bottom.

This is probably an artefact of your browser rescaling the image and messing it up. That's moire you're talking about.

For PAL lores or hires/interlace the pixel aspect is 44:44 or 22:22, respectively, so there integer scaling has no aspect ratio issues.

For NTSC, the pixels aren't square so there integer scaling does indeed produce a different aspect ratio. Which is a problem for software that sticks to the guidelines, but there's also a lot of software that just assumes square pixels on NTSC... so hard to win that war. And indeed, non-integer scaling in the horizontal direction, especially in lores, is rarely a problem. Each lores pixel becomes four or five LCD screen pixels, and having some be four and others five is not enough of a difference on regular content. Not good for alternating black/white pixels, though. But that's more a 1980s Mac thing.

And yes, the image gets darker.

Yeah, my scanlines do not darken the image.

Furthermore since all CRT's are based on an analog signal, integer scaling horizontally makes NO SENSE. This isn't just about maintaining perfect aspect ratio, but the simple fact that there is some blending on an analog signal from you Amiga, through a cable into the monitor. Allowing the horizontal to be linear filtered not only opens the door to precision scaling but softens the image slightly in the SAME WAY that CRT's do and helps blend dithering very nicely.

Yes, interlace is annoying. I have been experimenting with non-interlaced 25 or 30 Hz screen resolutions because that way I can use 256 colors without the CPU losing its chip mem access 50% of the time. But that's also not great, with the mouse pointer becoming very jerky. Only real solution here would be an RTG graphics card, but I don't think that's in the cards for my A1200... (A3000 does have one, but then again only 8 MB fast RAM and a 25 MHz 68030, so hard to take advantage of all that interlace-free screen real estate.)

Yeah, there's no one great solution out there. Your best bet would be to have 16:9 productivity modes (see previous post).

[iljitsch]

I would take both of those ratios as 1:1

I think you're on solid mathematical ground there.

but both analog and digital PAL signals do have a pixel aspect ratio that are not 1:1. Am I missing something here?

Well, analog video such as PAL doesn't have pixels. Of course it does have lines, and the horizontal resolution can also be expressed as a maximum number of lines. However, the bandwidth can be anything between 4.5 MHz for some TV broadcasts to more than 6 MHz for S-video, resulting in 500 to 600 or so lines.

You may have noticed that the Amiga goes well over that with 650 - 700 pixels per line. The Amiga's pixel clock is 14.32 MHz which would make for video bandwidth of 7.16 MHz (where have I heard that number before...?). With the result that alternating bright/dark pixels won't display crisply on a CRT from the NTSC/PAL era, which weren't designed for such a relatively high video bandwidth. As such, icons, fonts etc in OS 1.x rarely use a single pixel horizontally.

Anyway, then we got SD (standard definition) digital TV, most notably in the form of the DVD. For that, they use 576 "visible" lines for PAL and 480 for NTSC. The Amiga can go pretty far with overscan, but not quite that far. So a few of those lines are officially visible, but not in practice.

Now of course it would have been nice (as in: hip to be square) on our 4:3 screens to have 576 / 3 * 4 = 768 pixels horizontally for PAL and 480 / 3 * 4 = 640 for NTSC. However, that didn't happen. DVDs can encode 720 pixels across and use a 13.5 MHz pixel clock (i.e., a bit lower than the Amiga's).

Wikipedia has a nice list of the SD resolutions and pixel aspect ratios. They are off by less than 10% for both 480i (the SD version of NTSC) and 576i (the SD version of PAL) but of course in opposite directions... And the image can be stretched for 16:9 content.

Fortunately, with HDTV that's now all mostly a thing of the past, with 1280x720, 1920x1080 and 3840x2160 all using square pixels. However, monitors still often offer the option to use different aspect ratios and then the pixels are no longer square.

(For instance, with my Amiga 3000 I use a Cybergraphx card in 960x540 resolution over VGA. The monitor thinks that's 1920x540, but displays it as 4:3. So I need to tell the monitor to use 16:9 and 960x540 is stretched to 1920x1080 pixels, all nice and square.)

[fxgogo]

Thanks for the info. Yeah I do forget that analog video is pixelless. I remember many conversations with the engineers at work and how we saw video was so completely different. Gosh it was a messy time.

I really like the idea of integer vertical scaling and not for the horizontal.

The thing with us trying to get CRT looks is that everyone’s televisions and monitor were all set up differently. With some even having horizontal and vertical scaling. It is a never ending road, but fun to ride down.

[nonarkitten]

The thing with us trying to get CRT looks is that everyone’s televisions and monitor were all set up differently. With some even having horizontal and vertical scaling. It is a never ending road, but fun to ride down.

I agree with this, but while some aspects of CRT are good, some are not. If I might, where any artistic effect was used, especially when commonly used, that leveraged a weakness of the CRT format, then we should attempt to maintain that as best we can.

Where artifacts were seldom used for artistic or beneficial effect, then they should be removed.

Because to me, it's the preservation of the BEST these machines could offer that's important. After all, no one enjoys emulating the 20-minute load times of a Commodore 64. So dithering worked because of the high-pass filter on the analog video signal but still seemed sharp because of vertical separation or scanlines. It was also aided by PAL TV's performing luma blending, something only copper dragon's scaler does right.

Along with the near-zero latency (which is really hard to duplicate on LCDs), these were really its only good aspects. Composite or RF noise? NTSC artifacts? Spheroid-like screens with massive barrel distortion? CRT hum through the speakers? While we're at it, how about sync loss and lines that randomly jump around and bend when there's too much white on the line. Black and white? How crappy do we want to make our LCDs?

To me, the horizontal-linear, vertical-integer, overlay-scanlines does the LEAST AMOUNT to return the BEST visual integrity of the system for the time. And no more.

Now, let's figure out how to fix that latency issue. Anyone up for making a 480Hz upscalar?

[fxgogo]

Well said. Also remember the fatigue our eyes got by staring at that glowing orb for so long. I have been finding just having a shadow mask overlay is enough for me while doing my productivity and creative work in WinUAE. Enough of a fell of a CRT without all those draw backs you mentioned.

[iljitsch]

Also see this thread:

Retro gaming history is being distorted (and using GRABBiT)

Apparently discussions about pixel aspect ratios run the entire history of this forum.

[nonarkitten]

Also see this thread:

Retro gaming history is being distorted (and using GRABBiT)

Apparently discussions about pixel aspect ratios run the entire history of this forum.

The painful part is that for some reason it's never really been fixed.