Pixel OFF Turns Off Pixels to Save Battery on AMOLED Displays
Android: Phones with AMOLED displays have a unique battery-saving trait: the fewer pixels are activated, the less power they use. Pixel OFF helps you take advantage of this by activating only the pixel grid.
The app can turn off the grid of pixels of different densities depending on how much battery you want to save. Your phone will look similar, only slightly darker. However, since your display uses half the pixels (or less), the battery drain on the display should be reduced. Many modern phones have so many pixels that you can hardly tell the difference .
Pixel OFF also includes support for Tasker, so if you don’t want to keep it on all the time, you can only enable the grid based on specific Tasker conditions. For example, when the battery reaches a certain level or only when you are away from home.
Pixel OFF | Google Play Store via Android Police