how to get image size from opencv node.js library

Question

I'm using the node.js open cv library and I was wondering how to get the image width and height from what looks like a Matrix object

cv.readImage("./sample.jpg", function(err, im){
  var width = im.width;// this part breaks, how do I get width and height?

});

Answer 1

Use the width() and height() methods on the matrix:

im.width()
im.height()

Be careful though. It's easy to forget to use the parentheses, and then you will simply be referencing the function:

console.log(img.width) // [Function: width]
console.log(img.width + ''); // function width() { [native code] }

Of course, it's easy to spot the problem in these examples, but if you're not just logging the width and height, the issues may initially go unnoticed.