为什么我的canvas出来的图片是原图片的放大版啊？

var canvasWidth = 700;

var canvasHeight = 400;

var canvas = document.getElementById('canvas');

var context = canvas.getContext('2d');

canvas.width = canvasWidth;

canvas.height = canvasHeight;

var image = new Image();

image.src = "girl.jpg";

image.onload = function(e){

initCanvas();

};

function initCanvas(){

draw(image);

};

function draw(image){

context.drawImage(image,0,0);

};