unsafe fn decr<P>(&mut self, image: &Image<P>, x: u32, y: u32)
    where
        P: Pixel<Subpixel = u8>,
    {
        let pixel = image.unsafe_get_pixel(x, y);
        let channels = pixel.channels();
        for c in 0..channels.len() {
            let p = *channels.get_unchecked(c) as usize;
            let hist = self.data.get_unchecked_mut(c);
            *hist.get_unchecked_mut(p) -= 1;
        }
    }
Safety: requires x and y to be within image bounds and P::CHANNEL_COUNT <= self.data.len()
src/filter/median.rs