[Galaxy S 4 i9500 Android Development] puremind:
I did some more analysis of the display behavior. Essentially, the adaptative brightness without power saving options is to fool regular gamma testing and make it look flat even though it isn't - again to conserve battery!

Using Average Picture Level patterns, to keep brightness constant across the greyscale, we can clearly see that the gamma is too high (2.4).

By reducing brightness as IRE levels increase, the display conceals the fact that brightness increases too slow across the full IRE spectrium - because the final brightness ends up being lower, regular test patterns will say that brightness at each IRE level is where it should be when in fact it lags behind. It only catches up with target brightness at 100 IRE because brightness is being throttled more with each IRE level.

For example, at 50 IRE, the theorectical brightness should be 21.46% of white brightness, except the white brightness at 50% IRE is higher vs. 100% IRE. What is important is not the 100% IRE brightness, though. because it is throttled and has no impact on intra-picture gamma.

What is important is the 50% IRE brightness, which is higher. So while regular test patterns lead you to believe brightness is where it should be and gamma is 2.2, in fact it is lagging behind for the full brightness spectrum.

So in conclusion:

We need to recalibrate gamma on this display by using APL test patterns - they are the only ones that should ever be used on displays with adaptative brightness where brightness is a moving target.

OR

We need to deactivate the adaptative mechanism (which would have the secondary effect of improving overall brightness)

But as long at the adaptative mechanism exists, we will never be able to have perfect gamma at all APL levels. If we choose to have perfect gamma at 50% APL, we will have brightness below target for low APL levels (since the 50% APL brightness will be lower than at lower APL) and it will be ahead of target for higher APL levels (since the 50% APL brightness will be higher than at higher APL levels).

So in essence, because of the adaptative mechanism, we can never have a perfect intra-picture gamma that works equally well at all APL levels.

The standard error will be smaller at lower brightness levels because the peak brightness range will be more narrow. But in boost mode the max brighness will be 70%higher than minimum brightness, so the standard gamma error at low APL and High APL levels will be higher, so black crush will be quite big for low APL and white crush will be quite big at high APL.

In a nutshell, if we want perfect gamma, we will have to acccept lower intra-picture contrast at lower APL and equalize brightness on the maximum achievable non-thottling 100% brightness. Since the display is very linear, this should yield us perfect gamma and RGB balance for all brightness levels that the user chooses between 0 and max user-selected brightness.

On plasma displays, throttling typically only happens above a certain brightness level. and it is enough to stay within that comfort range But the fact that brightness is being modulated for different APL levels on the S4 makes a good calibration that works at all APL levels impossible...

I can't believe how imaginative Samsung is when it comes to fooling reviewers. The display has potential, I just know that calibrating this thing with undefeated adaptative brightness will not yield perfect results - unfortunately.

The mos pressing issue at the moment is the green push though and oversaturated colors, though. I am pretty sure that reducing color saturation will also impact greyscales and brightness on this display...A lot of fun coming our way