Is your wallpaper truly black?
Drop a wallpaper and see exactly what percent of it is true #000000: the black that switches AMOLED pixels off. Then snap the almost-black pixels to pure black and download a PNG. Runs entirely in your browser. Nothing is uploaded.
Left of the divider is converted, right is the original. Drag to compare.
Left of the dial only snaps near-black; drag right to force darker pixels to pure black too. The number above is the result: how much of the image is true #000000 at this setting.
Why isn't my black already black?
On an AMOLED / OLED screen, a pixel that is exactly #000000 is physically turned off: no light, no power. That's the true-black look and the battery saving. But a "black" area saved as a JPEG is almost never pure black: compression leaves it at #010101, #000001 and so on. It looks black to your eye, but those pixels are still lit. That's why a wallpaper can read 0% true black while looking completely black.
This tool snaps a pixel to #000000 when all three of its R, G, B channels are dark (at or below the dial). Snapping by the brightest channel means a deep color like a dark red stays a color; only genuinely near-black pixels get turned off. "Convert to true black" catches the obvious near-black; the dial lets you go as aggressive as you like.
Export is always PNG, never JPEG. JPEG compression would re-scatter the blacks right back to #010101 and undo the whole thing.