[Galaxy S 4 General] puremind:
Measured with i1 Pro 2 and profiled i1 Display 3 with the following settings:

We have all seen the side by side web browsing comparisons between the S4 and the HTC One. because of the screen reviews, which measured brightness at 300cd/m² and higher, we were a bit dubitative.

Well, it turns out the poor results are due to heavy (33%) brightness throttling on white or near white content during web browsing (surely in an attempt to fool the battery tests, seeing as this mechanism is stronger on the Chrome or Stock browsers than on other browsers). Brightness throttles (fluctuates based on content displayed): the larger the white surface (or the average picture level), the dimmer the whites (white clipping). The smaller the surface, the brighter.

Brian klug at Anandtech was the first one to point this out, though the extent to which this was happening was not revealed (perhaps due to the fact that he was conducting testing at 50% brightness for most of his review). I have conducted the measurements and: during web browsing, brightness is cut down by 33%, even at maximum system/browser brightness

In the table below you can clearly see that even with the brightness friendly settings (Power Saving and Auto Adjust Screen Tone turned to Off), brightness clipping is happening. In the best scenario (Film Mode), the clipping is 33%:

Measured with standard Voodoo test patterns, brightness is not great but not horrible but this gets worse on white content, and clipping is the strongest on the Chrome and Stock browsers:

On small surfaces, I was able to measure up to 355cd/m² (so essentially, smaller test patterns will yield a flat gamma)

On a 100% white test pattern, brightness is already clipped at 280cd/m²

When browsing, using the Chrome or Stock Browser, brightness is clipped even further down to 230cd/m². This is twice as dim versus the HTC One for Web Browsing. and explains why all the side by side comparisons made the S4 pale even though in theory the S4's peak brightness is acceptable.

There is a way to attenuate the clipping, though. You can use another browser than Chrome or the Stock browser. By doing so, the white clipping is limited to the UI white white clipping (so around 280cd/m² down from 350cd/m²), so is much less detrimental to sun legibility - at the expense of some battery life. For those of you that prefer Chrome or the stock browser, we can rely on Andrei to come up with a setting that bypasses the extra clipping mechanism.

So to all of you who want more brightness you can, but if you use other browsers then Chrome or the Stock Browser, your battery life will suffer significantly.

Other findings:

Gamma will also get worse on content that has a high proportion of bright content, with brightness compression happening at the top end of the spectrum.

RGB balance has a discernible green push above 50% brightness (less exposed in Anantech's review because Brian measures at 50% brightness rather than maximum)

Color Space is oversaturated even in film mode (consistent with Anantech's finding)

White point color Temperature:

6337cd/m² in Film Mode - again, this is at maximum brightness, the green dominance will be different at different brightness levels (as can be seen on the curves below)

6317cd/m² in sRGB Mode

6940cd/m² in Standard Mode, Dynamic Mode and Auto-Adjust Mode (I personally prefer that color temperature because it is more consistent across the whole scale, so the picture looks more harmonious)

Gamma is improved versus previous iterations but there is still a slight black crush and white crush happening at the extremities (nothing too major). The white crush will not be observed with smaller test patterns but will be worse for bright content! The black crush will be worse with Auto Tone on (to conserve battery, the transition into blacks is quicker).

Color gamut as expected is oversaturated. But what is more surprising is that it is oversaturated even in Film mode, although to a smaller extent. I went back to Brian's review, and this was also what he found. I believe two other reviews had different findings - but I may remember this incorrectly

Measurements in Film Mode

Color Space - Other Modes

Although the throttling is to conserve battery life, I find this a bit unfair to competitors because Samsung is tricking reviewers into overestimating battery life when they try and equalize brightness levels during their testing. So consumers think they have the best of both worlds (brightness and battery life). There is a choice that can and has to be made.