Gamma 2.2 or 2.4?

[tele1962]

As this was taking the Panasonic VT thread OT. I was wondering as I have been told on good authority that we should be aiming for 2.4 Gamma for Blu Ray and crucial viewing as opposed to 2.2?

 

[Skood]

We'll now Bt.1886 has been accepted as the gamma standard that's what I calibrate to, but only very recent releases will have been mastered to that - previously it could be anywhere from 2.2-2.4 depending on the studio.
A straight 2.4 may well crush blacks unless you are watching in a blacked out room -bt.1886 brings out dark details by having lower gamma at the dark end and higher gamma at the light end.

 

[Cynephyle]

you can calibrate from anything between 2.2 - 2.6, but I'd recommend 2.2 b/c that was and still is what pretty much everybody masters to for end consumer products...

 

[vism]

Could someone confirm something for me?

Is there any visual difference between something that was encoded and decoded with 2.4 gamma vs something that was encoded and decoded with 2.2 gamma?

 

[HeadBanger]

A straight 2.4 may well crush blacks unless you are watching in a blacked out room -bt.1886 brings out dark details by having lower gamma at the dark end and higher gamma at the light end.

Looking at the various reviews of the VT and ZT Panasonics they appear to have gamma lower (brighter) at the low IRE and higher (dimmer) at the high IRE (ref Rec709?) which the reviewers then calibrate out. So have Panasonic actually aimed for bt1886 (at the 2.4 setting) or is this just coincidence?

 

[Skood]

I noticed the same thing with my ST60 however if they were aiming for bt.1886 they did a fairly rubbish job.

When calibrating the ST60 I selected the 2.6 gamma preset as this gave the closest average gamma to 2.4 but it actually only really intersected the 2.4 curve at around 50 IRE. Gamma at 10 IRE was more like 1.8 and 80 IRE about 2.7 - at 90 IRE it actually dropped quite sharply to around 2.2.

While pattern sizes and ABL can have an effect on the gamma curve I got fairly similar readings using a mixture of window patterns from 5%-12% and also APL patterns.

A proper bt.1886 curve follows around 2.3 for most of it - it's only around 20 IRE where it drops fairly sharply towards 2.1 - however that depends on the black level of the display as bt.1886 is calculated on black level. Something like the ZT would very nearly be a straight 2.4 because of it's extremely low black level.

This is the gamma targets for bt.1886 on my st60 - this assumes a white level of 120cd/m2 and black level of 0.008 cd/m2. The st60 has good black levels so the drop is quite sharp below 10IRE - a screen that does not have such good black levels would curve down much earlier. This is why I prefer bt.1886 as it takes into account the limitations of the individual display rather that a one size fits all approach.

5% 2.16
10% 2.24
15% 2.28
20% 2.30
25% 2.31
30% 2.32
35% 2.32
40% 2.33
45% 2.33
50% 2.34
55% 2.34
60% 2.34
65% 2.35
70% 2.35
75% 2.35
80% 2.35
85% 2.35
90% 2.35
95% 2.36

On my LG Led a straight 2.4 would never work because of the ridiculously bad black levels but even 2.2 crushed dark detail in high contrast scenes due to the displays dimming technology. Bt.1886 helped the issue as that gave me a gamma of [email protected] and [email protected] and that brought out the dark details but still preserved the contrast in brighter scenes.

 

[Cynephyle]

Looking at the various reviews of the VT and ZT Panasonics they appear to have gamma lower (brighter) at the low IRE and higher (dimmer) at the high IRE (ref Rec709?) which the reviewers then calibrate out. So have Panasonic actually aimed for bt1886 (at the 2.4 setting) or is this just coincidence?

the VT60 gamma response depends on which gamma preset you're using and how long the screen's been on etc... I don't think they aimed for BT.1886...

you can see some examples of the gamma response and how to calibrate the gamma here:

Panasonic 65VT60 eeColor Lightspace Calibration Guide & Workflow Color Accurate Performance

as you can see some screens have a huge gamma spike towards a brighter gamma in the higher brightness range...

 

[xfilian]

My VT60 has been calibrated to 2.6 in the main setting. It averages out at just under 2.4 on the graph I have.

 

[AndreiNR]

That's true but with normal windows I presume. I would calibrate it with a -0.1 gama value if I would use normal windows. Take a reading with apl ones and tell me what you find(if you haven't done it all ready).