How to set it
- iPhone: save the image to Photos, then Settings, Wallpaper, Add New Wallpaper, Photos.
- Android: open the image in Photos or Gallery and choose Use as wallpaper. The menu names differ by phone maker.
- Windows: right-click the downloaded file and choose Set as desktop background.
- Mac: System Settings, Wallpaper, then add the downloaded file.
Why pure black
On OLED screens, which most recent flagship phones use, black pixels are switched off. A pure black (#000000) wallpaper gives off no light behind your icons and lets the screen look like one piece of glass. On LCD screens the backlight stays on, so black looks very dark gray. If you only need the screen dark for a while, the black screen tool does that without changing your wallpaper.
Questions
What size should I pick?
Pick "This screen" to match the device you are on. For a phone lock screen pick iPhone or Android phone; for a TV or monitor pick HD, 2K or 4K to match its resolution.
Is the image really plain black?
Yes. Every pixel is the exact color shown under the shade you picked, with no noise, logo or watermark.
Is anything uploaded?
No. The image is drawn in your browser and saved straight to your device.
PNG or JPG?
PNG keeps the color exact and a plain color PNG is small. JPG also works everywhere; use it if an app will not accept PNG.