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Original topic:

Q90R HDR highlight clipping

(Topic created on: 31-07-2020 03:49 AM)
FrankieSomeone
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TV

I only found a couple of posts on the internet mentioning this - when viewing HDR content the highlights get quite clipped, or rather they plateau and get squished at the top.

I have tried all kinds of calibrations and the only way to avoid this is to use the Movie profile with Local Dimming set to Low, which is not very good because it gets very dark and the panel won't dim at all unless it's entirely 100% black.

I believe this to be an intrinsic property of gamma st.2084 - some people might like it but I find very annoying that highlight details get erased, I thought one of the selling points of HDR was super bright reflections and highlights!

The pictures below are taken in Movie mode with Local Dimming set to High (it's the same with standard)
The picture without the clipping is what you see when you pop up the menu. It seems the highlights clip more the darker the overall screen is.

Come on Samsung, you can do better. At least give us a second gamma curve to choose from.

IMG_20200403_173959_1.jpg

 

IMG_20200402_191838.jpg

 

13 REPLIES 13
FrankieSomeone
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Thank you for writing that post btaiji. Very thorough analysis. It's so stupid that Samsung claims it's not a problem. It is for me!
Here's a picture to illustrate what I think is going on here. I think tonemapping is the culprit. Anyone feel free to correct me if I'm wrong.

FrankieSomeone_1-1596141935467.png

 

I think Samsung's goal is keeping average picture level high (bright image) -- as a film purist, I'd love to have the option to keep APL lower so I can see all the highlight detail.

btaiji
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I agree with you!

It seems that Samsung is setting a different 'feeling'

that they wants to show the viewers at each local dimming stage.

And not only changing the local dimming mechanism at each stage,

but also changing the tone curve,

and I don't think it's working properly.

The image you uploaded is quite convincing,

where did you capture the graph and curve? Photoshop?

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FrankieSomeone
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Yes it's a mockup I did in photoshop, based on my understanding of how tone mapping works.

It's strange that there aren't many references to this in reviews.
There's a brief mention here:
https://www.rtings.com/tv/reviews/samsung/q90-q90r-qled
in the picture quality/local dimming section
"it tends to dim the edges of bright objects, causing a vignetting effect, and small highlights like stars are crushed"
Again, I don't think this is caused by local dimming, but by the tone curve or something like that which is enabled when standard or high local dimming are selected. It can't be caused by local dimming alone (the actual LEDs in the screen) because the detail is missing from the pixels on the LCD panel. Local dimming simply lowers LED brightness, it doesn't erase detail.

I also noticed that the Standard picture mode handles highlights slightly better, but it crushes shadow detail.
Game Mode preserves all highlight detail and has darker black levels than Low local dimming, but it creates halos and it's only available for external sources.

btaiji
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I also don't think this is the problem of local dimming itself.

There must be something that applies to the pixel itself when I choose the dimming mode.

I wrote about SDR situation, and now I'm preparing for HDR.

There's something I found out on the way, the low setting also changes the highlight.

While standard or high setting burns the highlight gradient like white, low setting gently rubs the highlight.

Everything can't be perfect, but the low setting is the least annoying,

so I'm going to use the local dimming as low.

Since I set Contrast Enhancer to Low in SDR and High in HDR, I think dynamic range is good too.

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