html5: copy a canvas to image and back - image

Question

I implemented a zoom in and out function on a canvas element.
it works by scaling the canvas, translating it, and then redraw the whole scene again.
the problem is that it takes a lot of time to redraw everything because i got a lot of things on my canvas.
I need a way to copy the canvas to an image object and than copy the image back to the canvas without loosing quality. what are the specific methods to copy canvas to a javascript variable, and to to copy this variable back to the canvas later?
I'll be glad if you write down the code because I couldn't find any good explanation over the internet.
thanks,

Answer 1

The drawImage() method can draw to a canvas using another canvas instead of an image.
You could create a 'backup' canvas, of the same size as your original, draw the first one to there and then draw that one back to the original when you need it.
e.g.
// Assume we have a main canvas
// canvas = <main canvas>
ctx = canvas.getContext('2d');
..
// create backing canvas
var backCanvas = document.createElement('canvas');
backCanvas.width = canvas.width;
backCanvas.height = canvas.height;
var backCtx = backCanvas.getContext('2d');
// save main canvas contents
backCtx.drawImage(canvas, 0,0);
..
// restore main canvas
ctx.drawImage(backCanvas, 0,0);

Answer 2

There are a few ways to do it theres the getImageData and putImageData methods Reference, However putImageData and getImageData are pretty slow. Another way is to save the data to an image in memory and recall it from that which is much faster, then the third way is the one above mentioned by andrewmu which involves copying to another canvas element. I have included examples for the first and second type.
Image in memory method
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
savedData = new Image();
function save(){
// get the data
savedData.src = canvas.toDataURL("image/png");
}
function restore(){
// restore the old canvas
ctx.drawImage(savedData,0,0)
}
getImageData putImageData method
// Setup our vars, make a new image to store the canvas data
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
canvasData = '';
function save(){
// get the data
canvasData = ctx.getImageData(0, 0, 100, 100);
}
function restore(){
// restore the old canvas
ctx.putImageData(canvasData, 0, 0);
}

Answer 3

added image into canvas
var image = new Image();
image.src = "1.jpg";
image.onload = function () {
context.drawImage(image, 0, 0);
};