You can use the extended properties on context.drawImage that allow scaling/positioning.
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var img=new Image();
img.onload=function(){
var w=img.width;
var h=img.height;
canvas.width=w; // set the canvas size to the original image size
canvas.height=h;
ctx.drawImage(img,
0,0,w,h, // start with the image at original size
-w/4,0,w*1.25,h // widen the original image by 1.25X
// and start drawing 1/4th off the left edge of the canvas
);
}
img.src="temp18.png";