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samsung c27hg70 multichannel scanning backlight or not?

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samsung c27hg70 multichannel scanning backlight or not?

Postby strobeydobe » 12 Aug 2018, 07:09

Hey all, new here, huge fan of low persistence displays and the work you guys have done spreading awareness.

I was wondering if anyone knew for sure whether the chg70 had a multizone scanning backlight like the cfg70 and cfg73 series. The cfg70/73 are advertised to have 'impulsive scanning' and I have seen the results myself ie. low strobe crosstalk.

I am not sure if this is the case with the c27hg70 as the tft central review reports the c32hg70 having a crosstalk increase as you move down the panel (ctrl + f for crosstalk: http://www.tftcentral.co.uk/reviews/samsung_c32hg70.htm). This crosstalk increase pattern is fairly typical of single zone backlights. Additionally on samsungs website, impulsive scanning is not explicitly advertised on the chg70 series which leads me question whether it is a mulizone scanning or standard on/off backlight monitor.
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Re: samsung c27hg70 multichannel scanning backlight or not?

Postby Chief Blur Buster » 14 Aug 2018, 17:32

Very good question. I'll admit I am not sure.

That said, there's pros/cons of the two backlight approaches.

Full-Strobe backlight:
- Backlight flashes the whole screen all at once (once per refresh cycle).
- Works best on LCDs that has GtG fast enough to fit in the blanking interval between refresh cycles
- Very low or near-zero strobe crosstalk in the best area (e.g. screencenter)
- Much more strobe crosstalk in the worst area (e.g. screen very bottom edge)
- Simpler to engineer, sometimes hackable on an existing LCD that's not normally designed to strobe (can be usable if majority of its GtG is fast enough to fit in its VBI)

Scanning backlight:
- Backlight flashes out-of-phase with LCD scanout
- This can work well with IPS and VA LCD panels that has GtG too slow to cram into VBI
- More evened-out crosstalk
- For the same panel tech (Meaning a scanning backlight on a VA panel versus a strobe backlight on a VA panel) Evened-out crosstalk is usually slightly worse than "best area" of a full-strobe backlight, but much better than the "worst area" of a full-strobe backlight. How much better/worse it is depends on calibration and internal backlight diffusion (leakage of light from ON sections to the OFF sections).

Theoretically, the same monitor can do both. The ZWS 4K 120hz monitor (http://www.blurbusters.com/480hz) can flash all at once, versus scan top-to-bottom.
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Re: samsung c27hg70 multichannel scanning backlight or not?

Postby RealNC » 14 Aug 2018, 17:40

Even though I never saw a scanning backlight strobe in action, I think another advantage would be less severe flicker?
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Re: samsung c27hg70 multichannel scanning backlight or not?

Postby Chief Blur Buster » 14 Aug 2018, 19:30

Yes, that too. It can be roughly 25% less flickery at the same persistence setting. e.g. 100Hz scan roughly equal to 120Hz fullstrobe.

This can be important for usability of 60Hz flicker for consoles, but extremely few scanning backlights work at 60Hz either.
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Re: samsung c27hg70 multichannel scanning backlight or not?

Postby strobeydobe » 15 Aug 2018, 04:06

Hey thanks for the response. I asked Samsung customer service a question and they said they have forwarded it to their support team. I’ll post an update when I get an answer. I’m really curious.
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