Function quantize_colors 

pub fn quantize_colors(
    path: &Path,
    depth: u8,
    size: u32,
) -> Result<Vec<Color>, String>

The main colors of the image file at path, most common first.

The file is decoded as Image decodes it, under the same caps, then halved until its longer side is at most size pixels; 0 keeps its size. Its pixels are split by median cut into up to 2^depth boxes, with depth clamped to 0..=8: each time, the box with the widest range on one channel is split at its median on that channel. Each box gives the mean of its pixels, opaque. Pixels with alpha under 128 are skipped. Boxes with as many pixels as each other go by their color’s bytes, so a result is the same on every run. An image with fewer distinct colors than boxes gives each of them once.

Decoding a wallpaper takes tens of milliseconds, so call it off the loop’s thread.

Errors

If the file is missing or isn’t a regular file, isn’t a PNG, JPEG, GIF, WebP or SVG, is past the caps, or doesn’t decode.