I have problem drawing an image to a canvas with the right size.

This is my simple code: 

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

        $(canvas).css('width', '100px');
        $(canvas).css('height', '75px');

        context.drawImage(img, 0, 0, 100, 75);

```

I would expect the image draw on canvas to be 100 width and 75 height. The outcome is not that size but rather smaller size 

like this: 
![enter image description here](https://i.stack.imgur.com/Vldjt.png)

Expected the flower on the top corner fill up the whole red area.
Does anyone know the reason?