The Sony Xperia Z5 series actually has a 25MP multi-aspect primary camera sensor
According to some new evidence, it looks like the new sensor on the Sony Xperia Z5 series actually has a resolution of 25MP, although the photos you can extract from it are limited to 23MP due to the difference between the two standard aspect ratios. When shooting in portrait mode - a 4:3 aspect ratio - the sensor is capable of taking photos at 5,520 x 4,140 pixels (23MP). In landscape - 16:9 aspect ratio - mode, the camera takes photos at 5,984 x 3,366 pixels (20MP).
Landscape crops from portrait sensors
What this means is that the advertised resolution of the primary camera on most smartphones is accurate only with the camera set up in 4:3 mode. When taking photos in 16:9, like most users tend to, most smartphones actually take a portion - commonly called a crop - of that native 4:3 photo and turn it into a 16:9 one. Here's how this plays out visually:
Multi-aspect sensor on the Xperia Z5 series
According to preliminary evidence uncovered by GSM Arena, the Sony Xperia Z5 series actually comes with a 25MP with a native aspect ratio that's taller than 16:9 and wider than 4:3. In technical terms, the phones use a multi-aspect sensor.
When the smartphones shoot in 4:3 mode, the camera crops the native resolution picture at maximum height. When the camera sensor on the Xperia Z5 series is set to 16:9 mode, the camera serves a crop at maximum width. This way, the camera is capable of taking 16:9 photos at a resolution of 5,984 x 3,366 pixels, or about 20MP. If this really were a 23MP sensor as Sony advertises it, the resolution of the 16:9 photo would be 5,520 x 3,105 pixels, or 17.14MP.