extern crate image;
extern crate num_complex;

fn main() {
    let imgx = 800;
    let imgy = 800;


    // Create a new ImgBuf with width: imgx and height: imgy
    let mut imgbuff = image::ImageBuffer::new(imgx, imgy);

    // Iterate over the coordinates and pixels of the image
    for (x, y, pixel) in imgbuff.enumerate_pixels_mut() {
        let r = 0 * x as u8;
        let b = 0 * y as u8;
        *pixel = image::Rgb([r, 0, b]);
    }


    // Save the image as “fractal.png”, the format is deduced from the path
    imgbuff.save("fractal.png").unwrap();
}

渐变，替换这2行

let r = (0.3* x as f32) as u8;
let b = (0.3* y as f32) as u8;