IPhone 6-8 was 2x resolution at 750x1334
IPhone 6+ to 8+ was 3x resolution at 1242x2208 but down sampled to 1080 which provided a small performance hit (reason for sometimes performance hiccup in plus devices compared to non plus
IPhone X is 3x resolution at 1125x2436 with no down sampling
Now if you combine no down sampling which causes a single digit percentage blur plus oled screen and higher resolution you have the sharpest iOS device ever
Visualized here https://www.paintcodeapp.com/news/ultimate-guide-to-iphone-resolutions
IPhone 6+ to 8+ was 3x resolution at 1242x2208 but down sampled to 1080 which provided a small performance hit (reason for sometimes performance hiccup in plus devices compared to non plus
IPhone X is 3x resolution at 1125x2436 with no down sampling
Now if you combine no down sampling which causes a single digit percentage blur plus oled screen and higher resolution you have the sharpest iOS device ever
Visualized here https://www.paintcodeapp.com/news/ultimate-guide-to-iphone-resolutions