On both, a 12-bit RGB LUT is loaded in hardware, but as you can see on the curves in these graphs, the panel being only 8-bit, there's some banding going on.
I started working on another driver approach that allows to avoid this 8-bit limitation and permits extremely precise correction.
The target for both is D65 white point (as seen by the sensor for simplification), gamma 2.2 curve with a fine-tuned near-black response to avoid clipping or visual artifacts in shadows and near black, also preserving the color balance as much as possible near black.
The replacement Nexus 5 stays better even when both are calibrated thanks to its higher native brightness, slightly higher contrast ratio, and better consistency in its RGB channels which requires less correction.
Although beside the brightness difference which is appreciable, they look the same.
On both, the grayscale Delta E stays below 1 which is a very good accuracy despite the current 8-bit per channel driver hardware limitation.
Subjectively, it also looks pretty darn good 🙂
Maximum brightness – significant difference
original: 381 cd/m², replacement 474 cd/m²
original: 862:1, replacement: 891:1
On both, HCFR calculates an average gamma value of 2.18 without black point compensation and 2.21 with.