Gamma question

[Steve Smith]

Hello Florian

What’s the difference between Gamma 2.2 – sRGB – power gamma – ITU BT.1886 – and sliding gamma?

Does ‘Gamma 2.2’ – ‘sRGB’ – and’ Power gamma set to 2.2′ Produce the exact same results?

Which of the above gamma formulas is best for an HDTV connected to computer?

Thanks for any gamma understanding you can provide.

Also, can I create a 3D LUT and use it without the use of an external box? Can 3D LUTs be somehow stored and implemented in the computer itself… What’s a ‘virtual LUT’?

Thanks.

• This topic was modified 7 years, 1 month ago by Steve Smith.

[Florian Höch]

What’s the difference between Gamma 2.2 – sRGB – power gamma – ITU BT.1886 – and sliding gamma?

Gamma 2.2 is a power function, i.e. it follows a curve shape that is defined by the exponent (in this case 2.2). sRGB is a 2.4 power function with a straight segment near the dark end, so the overall shape of the curve is relatively close to a power function with exponent 2.2. BT.1886 takes the black and white level of the actual display into account and offsets the ideal curve input values to accommodate for the display black level. Sliding gamma is a similar concept, but with freely selectable exponent.

Does ‘Gamma 2.2’ – ‘sRGB’ – and’ Power gamma set to 2.2′ Produce the exact same results?

No.

Which of the above gamma formulas is best for an HDTV connected to computer?

BT.1886 is standardized for HDTV.

Also, can I create a 3D LUT and use it without the use of an external box?

madVR can use 3D LUTs.

What’s a ‘virtual LUT’?

That ought to be a CalMAN concept. It refers to a quick temporary 3D LUT that can be used to determine if and by how much a more full-blown 3D LUT would improve your display, without specialized 3D LUT hard- or software.

Something similar can be had in DisplayCAL by simply running a reduced set of profiling patches (say, a few hundred instead of over thousand), creating a 3D LUT and verifying it.

[Steve Smith]

Thanks Florian

So, in DisplayCAL, is choosing “Rec. 1886” for the tone curve exactly equal to choosing CalMAN’s  “ITU BT.1886” setting? … But what about the ‘Black offset’ and ‘Black Correction’ settings in DisplayCAL? … How should they be set to achieve the same curve produced by CalMAN? (Which only seems to offer a fixed ‘ITU BT.1886’ setting.)

What I want to end up with in DisplayCAL is a gamma curve ITU BT.1886 set to 2.4, but adjusted for the black and white points of my monitor. I want a final gamma of 2.3.   (What is your program’s equivalent settings to achieving this result?)

Thanks!

• This reply was modified 7 years, 1 month ago by Steve Smith.
• This reply was modified 7 years, 1 month ago by Steve Smith.

[Florian Höch]

So, in DisplayCAL, is choosing “Rec. 1886” for the tone curve exactly equal to choosing CalMAN’s “ITU BT.1886” setting?

Yes.

But what about the ‘Black offset’

When you change black offset, it will no longer be BT.1886 (and this will be reflected in the UI).

What I want to end up with in DisplayCAL is a gamma curve ITU BT.1886 set to 2.4, but adjusted for the black and white points of my monitor.

BT.1886 is always adjusted for black and white level of the monitor, that’s the whole point.

I want a final gamma of 2.3.

That’s fine, but not BT.1886 then. BT.1886 uses a fixed exponent of 2.4, and the effective gamma you end up with is determined by display black and white level.

[Steve Smith]

Well I guess that I can use BT.1886 then because with my particular display I end up with an effective gamma of 2.3. Which is what I am looking for.

Just want to get the same result with DisplayCAL that I got with CalMAN using BT.1886.

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