Function encode 

pub fn encode(
    image: &DynamicImage,
    format: Option<ImageFormat>,
) -> Result<Vec<u8>, ConvertError>

Scales an image into the limits of the API, and encodes it.

A JPEG stays a JPEG. Each other format becomes a PNG, so that text stays sharp.

Errors

Returns ConvertError::Size if no scale fits the image, and ConvertError::Decode if the encoder fails.