Comment by crazygringo

Comment by crazygringo 4 days ago

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> then the final result is raster-scaled with some sinc/Lanczos algorithm back down to the physical resolution. This shows up as ringing artifacts, which are very obvious with high-contrast, thin regions like text.

I don't think this is true. I use non-integer scaling on my Mac since I like the UX to be just a little bit bigger, and have never observed any kind of ringing or any specific artifacts at all around text, nor have I ever heard this as a complaint before. I assume it's just bilinear or bicubic unless you have evidence otherwise? The only complaint people tend to make is ever-so-slight additional blurriness, which barely matters at Retina resolution.

kbolino 4 days ago

Indeed, these artifacts sound like they're coming from Display Stream Compression [1] rather than scaling. I've had Macs occasionally use DSC when it wasn't necessary; power-cycling the display and/or changing the port it's plugged into usually fixed it. If it's consistently happening, though, it's probably because the display, the cable, the port, and/or the GPU can't handle the resolution and refresh rate at full bandwidth.

[1]: https://en.wikipedia.org/wiki/Display_Stream_Compression

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delta_p_delta_x 4 days ago

> ringing or any specific artifacts at all around text

There are a few Reddit threads that crop up when one searches for 'macOS ringing artifacts scaling'. For instance, these ones:

https://www.reddit.com/r/macbookpro/comments/1252ml8/strange...

https://www.reddit.com/r/MacOS/comments/1ki58zk/fractional_s...

https://www.reddit.com/r/MacOS/comments/l8oadr/macos_fringin...

All are ringing artifacts, typical of downscaling. I no longer have a Mac (chose one for work to try it out, saw this issue, returned it immediately), but I assure you this is what happens.

> The only complaint people tend to make is ever-so-slight additional blurriness

At no scale factor should there be any blurriness unless a framebuffer resolution is explicitly set. The 'scale factor' should be entirely independent of the physical resolution, which macOS simply does not do.

Apple's understanding and implementation of 'Retina' comes from a singular source: the straightforward doubling in each dimension of the display resolution of the iPhone 4 compared to the iPhone 3GS. It has not changed since, and has applied this algorithm throughout its OS stack.

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  • crazygringo 4 days ago

    All of these involve external monitors as far as I can tell, so it seems more likely it's the Display Stream Compression mentioned by the sibling to your comment that is the culprit.

    Like I said, absolutely nothing like that happens on my display. I see the ringing in the first link. That doesn't happen to me. Not even a hint of it.

    I get you don't like the scaling, but like I said, the very slight blurriness just isn't really noticeable in practice, especially given how Macs antialias text to begin with. Of all my complaints about Macs, this particular one is close to the bottom.

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    • kbolino 4 days ago

      I gotta say, as the guy who brought up DSC, that last Reddit post especially had me doubting. That is not what DSC artifacts look like. DSC subsamples the chroma, which causes distinct color bleeding issues. That is luma bloom, which doesn't happen with DSC.

      So I took my Mac Mini, hooked up to a 4K monitor, verified there were no DSC artifacts at native resolution, set it to "2560x1440" and sure enough the same artifacts appeared for me too, but still no telltale signs of DSC. So yeah, I gotta say, this is on Apple. Between this and dropping subpixel antialiasing support for text, it's pretty clear that their only properly supported configuration is 2x scaling on high-DPI displays.

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      • crazygringo 4 days ago

        Huh, very interesting.

        OK, I just grabbed my loupe to make sure I'm not missing anything, and pulled up an app in dark mode (so ringing should be more visible) on my MBA M4. I'm using its built-in display. I've cycled through all 4 available resolution settings in Display, and absolutely zero artifacts or ringing. Then tried connecting to my LG UltraFine 4K which connects over Thunderbolt, that gives 5 resolution settings instead of 4, and zero artifacts/ringing on any of those either.

        So I have no idea what's going on. I don't doubt that you're seeing it, and it's there in that Reddit photo. But maybe it's something specific to external monitors over a certain connection type or something? Seems very strange that Apple would use a different downsampling algorithm under different circumstances though.

        I'd normally assume the most likely culprit would be some kind of sharpening setting on a monitor, as that can absolutely cause the type of ringing seen in that Reddit photo. But on the other hand, if you're testing it right now and not seeing it at native 2x, then that would seem to be ruled out, at least in your case. Maybe it's some kind of resolution negotiation mismatch where it's actually the monitor applying a second scaling that has ringing, since monitors can accept signals that don't match their native hardware resolution?

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        • kbolino 4 days ago

          I can get a mild form of it on my M4 MBP's built-in display at "1800x1125"* but it's not nearly as noticeable as it was on the 4K external display at "2560x1440" and honestly I needed my cell phone camera zoomed in to definitively identify it, so that was more of a fishing expedition than a real problem. However, I have tried 2 different Macs, 2 different 4K monitors (both LG UltraFine also, though they differ in firmware version and color reproduction because of course they do), and 2 different interfaces (HDMI, Thunderbolt), and I can reliably replicate it under all of those combinations. I think that exact scaling factor probably has a bad interaction with the scaling algorithm. I do agree that a lot of other scalings do not produce the ringing/halo/bloom effect.

          * = You have to go click "Advanced...", enable "Show resolutions as list", then when back on the main Displays page, enable "Show all resolutions", to get this and many other options -- but this is only necessary on the internal display, the external display offers "2560x1440" as a non-advanced choice

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    • delta_p_delta_x 4 days ago

      > All of these involve external monitors as far as I can tell

      This happens on the native displays of MacBooks and iMacs, too. Try any of the 'looks larger'/'looks smaller' settings and it'll show up.

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      • crazygringo 4 days ago

        I've repeatedly explained that's not the case. Not on any Mac I've ever owned, and I already explained I thoroughly investigated my current M4 MBA. It's not showing.

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