16bit grayscale image from u8 buffer about image HOT 2 CLOSED

let mut img_bytes: Vec<u8> = Vec::new();
let mut buffer: Vec<u8> = Vec::new();
// buffer gets filled from a tcp read

// Reading 16 bit grayscale image from memory buffer"

 // We have to convert the buffer of u8 to a buffer of u16.  
// I don't know a better way to do this but 
let mut pixel_data = Vec::with_capacity(buffer.len()/2);
for i in (0 .. buffer.len()).step_by(2){
       let val = LittleEndian::read_u16(&buffer[i..i+2]);
       pixel_data.push(val);
}
                    
debug!("Converting to dyn image (luma16)");
let img_buf = ImageBuffer::from_raw(payload.width, payload.height, pixel_data).unwrap();
let dyn_img = DynamicImage::ImageLuma16(img_buf);

let mut output_buffer = Cursor::new(buffer);
let encoder = image::codecs::png::PngEncoder::new(&mut output_buffer);
// writing 16 bit lumaA image to buffer"
encoder.write_image(dyn_img.as_bytes(), payload.width, payload.height, image::ColorType::L16)?

img_bytes = output_buffer.into_inner(); ///  my result