Function sixel_string 

pub fn sixel_string(
    bytes: &[u8],
    width: i32,
    height: i32,
    pixelformat: PixelFormat,
    method_for_diffuse: DiffusionMethod,
) -> Result<String, SixelError>

Encode image bytes to a String containing the sixel data.

The bytes must match the width, height, and “pixelformat”.