Local zone dimming issues: distracting bloom, lines, and dark rectangle

Hello!

I have a few different issues that feel linked, so I’m posting them as a single topic.
While many aspects of the Spectrum are very nice, image quality when in HDR mode is made disastrous by these issues. Hopefully they can be mitigated in software :slight_smile:

I’m using firmware 105, and most of these issues were there in 102 as well. They’re all present only when the screen runs in HDR mode. They all happen whether the screen is connected to my Monterey MacBook via USB-C, or my Windows 10 PC via DisplayPort.
Of note! The videos I’m linking to are themselves recorded in HDR, encoded in HEVC, so they might look weird or blown out, depending on your computer/OS/video app.

Strong contrast between dimming zones

The Spectrum’s vertical dimming zones are pretty chunky, and sometimes have drastically different brightness; this results in extremely visible blooming, which is super distracting when watching a movie.
Here’s an occurrence of contrasting zones. On the right, as some small points of light shine through the window, the whole right side of the image lights up. The effect in the recording is much softer than what’s actually seen in person.

I also tried recording playback of this HDR stress-test: the result shows blooming a lot more clearly.

Backlight change produces flashes

In some situations, the backlight’s change in brightness causes the screen to very visibly flash whenever a white subtitle becomes visible, or goes away. You can see a subtitle flash happen six times in this recording. Once again, it’s even more visible IRL than in the recording.
I mitigated this by making subtitles dark gray wherever I could… which makes them a lot harder to read!

Interference line between dimming zones

For some reason, dimming zones seem to often interfere in a way that produces a very visible vertical line, that slides left and right as the brightness changes. You can see the line move around in this recording, on the left of the screen.

Darkened rectangle to the left of the screen

This one feels a lot more like a hardware defect in my unit. In some situations, a darkened rectangle appears on the left of the screen, towards the middle. This is not a rendering glitch, as I’ve seen it happen both in games and movies, and both on the Mac and the PC.

You can see the rectangle in this recording of Receiver II, running (I think) in windowed fullscreen on Windows 10.

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I also experience some of the same issues. Especially the bright flashes when subtitles are on is the most distracting thing for me. It makes watching movies and TV-series (as well as some games) unbearable due to the bright flash. I understand that the monitor only has 16 vertical dimming zones, but this issue should be fixable for a monitor of this price and stature.

Hi @Cykelero,

This is expected behaviour from local dimming. The stress test video shows backlight banding exactly as it is expected to work – the bright spot moving around increases the average brightness for that zone, so the backlight becomes brighter there to enable that.

The spot of light blooming video shows something similar: as the lights in the windows (can’t tell if it’s inside or reflections) becomes obscured by/visible past the plant, that makes a bright spot appear and disappear in that area of the screen, therefore the backlight zone it is in response to that by brightening and dimming. I can see how this example makes the backlight flicker, and of course, it’s not ideal.

But in the end, both of these cases are the natural result of local dimming with limited backlight zones. I’d expect them to occur with any monitor using local dimming (how noticeable it is will depend on the number of backlight zones).

The effect described as ‘interference lines’ may be a result of the same, not entirely sure there.

I don’t see any solutions for mitigating this. The real solution would be to increase the number of backlight zones, which is a hardware change.

That said, the ‘darkened rectangle’ seems to be some unevenness in the backlight diffuser layer, and might be an actual issue. Please contact support to look into this further.

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I understand! It does seem like it’s the number of dimming zones that’s way too low for a good HDR experience.
But: it also feels like smarter software could definitely help here. Both temporal smoothing (don’t immediately dim zones) and spatial smoothing (light up adjacent zones more than strictly necessary) would probably make things nicer, for instance.

I’ll contact support about the rectangle, thanks!