Function lodepng::auto_choose_color

pub fn auto_choose_color(mode_out: &mut ColorMode, image: *const u8, w: usize, h: usize, mode_in: &ColorMode, auto_convert: AutoConvert) -> Result<(), Error>

Automatically chooses color type that gives smallest amount of bits in the output image, e.g. grey if there are only greyscale pixels, palette if there are less than 256 colors, ...

The auto_convert parameter allows limiting it to not use palette.

updates values of mode with a potentially smaller color model. mode_out should contain the user chosen color model, but will be overwritten with the new chosen one.