HDR WTF ??

[gilesgoat]

"Micro Rant mostly to/for Dio interest" ( I suppose ) ..

So I am getting "a bit nuts" dealing with "color space conversions" from SRGB to HDR ( don't ask ) ..

To this date I YET have to see "what this HDR does/where it REALLY is/what it can do" ...

I mean when I think "HDR" I think "at an image of a sunset with palms on the screen" I can see the details on the things on the shadows of the palms as well as a sun that blinds me on a screen.

*BUT THAT DOES NOT HAPPEN* no screen I ever seen ( so far ) does that "at best" I see something that I can too obtain "via photoshop" by "playing a bit with curves" ..

So I am "getting banana" with ITU this .. ITU that .. BT2100 .. PQ .. HLG .. but for me the MAIN problem is that 10:10:10:2 leaves ONLY 2 BITS FOR ALPHA !! Which is piss poor so I can't use it directly ..

Anyway I do all this crap .. and I see a result that it's like .. "HUM .. hum .. is that correct ?" ...

So WTF this HDR ? "Does it really exist ?" .. Where ? How ? When ?

Someone told me a long story that took him "weeks of testing" like "but even if you have an HDR TV and NOT THE PROPER HDR bandwidth cables you DO NOT GET the proper HDR" ..

SO WTF ? WTF IS THIS HDR ?? DOES IT WORK ?? HOW you know when it works ?!!

[rowan]

I was talking to my bro about photography & HDR, as he was saying these days with more bits in each colour sensor, it is now much more about fiddling around with software than really careful camera + lens setup. You can just "drag stuff out of the darkness" of a "not wonderful shot".

On the topic of HDR in any games he was of the opinion that it's kind of artificial.
Anything that "really looks like it has it" has basically exaggerated it to the point that it's an effect, rather than anything which looks real.

Short story: I may be wrong but I reckon it's a load of buzzword bollocks to sell stuff.

[Dio]

The point about most game HDR is that it's going on all the time and most of the time you don't notice it - because modern physically based, tone-mapped renderers are rendering into a HDR subspace pretty much continually.

The last bit of it, taking the game's HDR and turning it into HDR on the user's retina, is a total fracking nightmare, because:
- monitors are not well conditioned devices
- monitors don't talk to PCs about HDR
- actually getting higher dynamic ranges (generally "really bright stuff" and "really dim stuff" on a monitor is vastly harder than it looks (think about the amount of watts you need to pump out of the screen to e.g. look at the sun).
- eyes are not very well conditioned devices too
- ambient lighting is an enormous problem (HDR works better in dark rooms, but then the ambient light is 'wrong' if the scene is bright). I suspect this is one of the things that makes almost all exaggerated HDR feel artificial because it only looks 'right' if the ambient conditions are correct.

The result is that if the game outputs X, you get 'something that looks like X' out as Y on the screen. Exactly what the transfer function is between Y and X is all of A. rather complicated B. not well understood by anyone without a PhD in it and C. loads of the key parameters that you might use to calculate f(X) are missing.

The theory I've had for a while (and promoted at work) is that we will really only get HDR working properly on a VR headset, where all the problems except 'really bright stuff' can be fairly definitively solved (since 'everything the user can see' is generated by the screen and the parameters of the screen can be strictly defined).

But if I'm honest I think it's back in a lull and it will stagnate for another 5-10 years before the next push to get it right.

[gilesgoat]

The point about most game HDR is that it's going on all the time and most of the time you don't notice it - because modern physically based, tone-mapped renderers are rendering into a HDR subspace pretty much continually.

The last bit of it, taking the game's HDR and turning it into HDR on the user's retina, is a total fracking nightmare, because:
- monitors are not well conditioned devices
- monitors don't talk to PCs about HDR
- actually getting higher dynamic ranges (generally "really bright stuff" and "really dim stuff" on a monitor is vastly harder than it looks (think about the amount of watts you need to pump out of the screen to e.g. look at the sun).
- eyes are not very well conditioned devices too
- ambient lighting is an enormous problem (HDR works better in dark rooms, but then the ambient light is 'wrong' if the scene is bright). I suspect this is one of the things that makes almost all exaggerated HDR feel artificial because it only looks 'right' if the ambient conditions are correct.

The result is that if the game outputs X, you get 'something that looks like X' out as Y on the screen. Exactly what the transfer function is between Y and X is all of A. rather complicated B. not well understood by anyone without a PhD in it and C. loads of the key parameters that you might use to calculate f(X) are missing.

The theory I've had for a while (and promoted at work) is that we will really only get HDR working properly on a VR headset, where all the problems except 'really bright stuff' can be fairly definitively solved (since 'everything the user can see' is generated by the screen and the parameters of the screen can be strictly defined).

But if I'm honest I think it's back in a lull and it will stagnate for another 5-10 years before the next push to get it right.

.. as I tought ... also "to throw another thing in the middle" ... TWO IDENTICAL MONITORS ( rare case ), SAME program, SAME settings ... "SRGB whatever the fuck I know from a PC" DOES NOT LOOK *PRECISELY* the same as 8_8_8_8_SRGB on PS4 maybe the gamma is lightly different ? As far as I understood should be 2.2 in all cases ( but I read mention somewhere of a 2.4 ) ..

CAN'T THE MONITOR/PC industry (*"£()$*()£*$()"$(£" agree on SOME standards ???!!

Mind you "all this goes apeshit" the moment the user will start simply setting a different contrast/luminosity/"image profile" most monitors allow so it's COMPLETELY POINTLESS !

Mind you YEARS ago I did ask "too big company" about "have you ever noted that if you try this on PC and you connect it to the same monitor and then you try with <console> on the same monitor the colours look a bit different ?" .. Answer ... "HUH .. NO .. we NEVER TRIED THAT COMPARISION .. " ...

"On this monitor, in THIS room, with THIS calibration with THAT light with THOSE people watching in the year of the Lord 2023 in the town of London all ye in this place made an oath to say 'It was looking OK' " ..

ANYWHERE ELSE IN THE WORLD *WILL NOT* look anything like that .. ..

Why we even spend time trying to ...

[Dio]

A 1-year-old version of the same display will look noticeably different to a new one - the only solution is to recalibrate, but even that is mostly just an exercise in curve fitting.

There are some enormous lookup tables lurking inside reference devices...

Oh, and just because it's the same monitor, it's not necessarily the exact same panel inside...

[Whiteball]

Nvidia drivers on PC still default to limited colour range if I remeber correctly.
All PC monitors will look better if it is set set to Full range, where as with a TV it depends on the settings on the TV being set too.
Basically as long as they match you should be ok so both limited or both full range.
Not sure if it applies only to HDMI or not.
Not sure if it is even relevant, but thought it worth a mention.

Consoles will be different again and have probably changed since the last gen - maybe.

[skab]

A 1-year-old version of the same display will look noticeably different to a new one - the only solution is to recalibrate, but even that is mostly just an exercise in curve fitting.

This. In 2004 I bought a 21" Samsung LCD monitor, then, when the used ones prices went down, bought some additional ones, one by one.

Those were rather traditional, older PVA panels, so quite slow ones. You could see a significant smear when moving the mouse pointer. One of those monitors (earliest make date) had the pointer smear in white, all others in black, so they changed something in the panels.

Then there was a massive difference in brightness and white point between my original, heavily used one and one of the later ones, which was obviously only barely used. The others were somewhere in between. I had 4 of those in a row, or rather a curve, which was a very practical and awesome looking setup, but getting all 4 calibrated properly so that they looked at least somewhat the same was a nightmare...

[Dio]

Yeah. It's improved a bit nowadays - LED inherently has much less of a colour shift over lifetime than the old CCFL tubes that most 00s monitors used - but they definitely dim.

[GoatFoam]

What do you mean by "srgb to hdr" exactly? Linear sRGB as a colour space can be used with HDR data just fine as it is. Presumably you are talking about the tone mapping to low dynamic range and gamma correction aspects?

I used to do a hell of a lot of that for work. Can give you a primer next time I'm on the IRC channel or discord.

[GoatFoam]

Also. CIE xyY FTW when tone mapping. Don't ask

[Little stoned kiwi]

Do you remember when a pixel was just a few bits that chose the colour from a small index? Pepperridge Farms does.

[zip accident]

Is there really anything more to HDR than shifting the darkness and brightness of pixels away from the midrange?

[Dio]

Yes.

[zip accident]

Yes.

Thinking about it, that should have been toward the midrange, not away.

I remember the computer enhanced photos from the late 1960s onwards from I think the FBI and CIA, they seemed to be little more than making the dark stuff not so dark. I assume there's a curve to it, how much worse than a curve is it?

[Dio]

It's a deep hole, as I discussed above.

Basically you have to control as much as possible of the whole process from the equations used to render original images on the screen, any postprocessing, the transfer from the computer to the display device, the display device's processing, the appearance on a panel whose characteristics vary both at manufacture and further with age, then the transport to the eye, which includes the effects of the ambient environment and even the history of what the eye has recently been exposed to.

Every stage has a complex mess of nonlinear functions, most critically of which there are several clamp and step points (e.g. how many values are there inside the computer or on the display to represent the pixel or what the maximum value that can be handled is).

The core of HDR is perhaps well summed up as "better matching those steps and clamps to reality". Increased maximum brightness and higher colour depth are "easy" things to throw at the problem and definitely give you More HDR, but it's not necessarily a big step towards fixing the real underlying problems.