Tresdin Tresdin - 29 days ago 6
Javascript Question

How to resize then crop an image with canvas

I already know how to

-> resize an image:

var image = document.getElementById('myImage'),
canvas = document.createElement('canvas'),
ctx = canvas.getContext('2d');
ctx.drawImage(image,0,0,400,300);


-> or crop an image:

var image = document.getElementById('myImage'),
canvas = document.createElement('canvas'),
ctx = canvas.getContext('2d');
ctx.drawImage(image,50,50,image.width,image.height,0,0,50,50);


But I don't know how to resize then crop an image. How could I do this? Thank you.

Answer

From the documentation, these are the parameters for drawImage:

drawImage(image,
    sx, sy, sw, sh,
    dx, dy, dw, dh);

enter image description here

So, to crop the outer 10 pixels from the source image (Assuming it's 100 * 50), and then to scale that up to 160*60:

ctx.drawImage(image,
    10, 10,   // Start at 10 pixels from the left and the top of the image (crop),
    80, 30,   // "Get" a `80 * 30` (w * h) area from the source image (crop),
    0, 0,     // Place the result at 0, 0 in the canvas,
    160, 60); // With as width / height: 160 * 60 (scale)

Example:

var image = new Image(),
    canvas = document.getElementById('canvas'),
    ctx = canvas.getContext('2d');

image.src = 'https://www.google.nl/images/srpr/logo3w.png';

image.onload = function(){
    ctx.drawImage(image,
        70, 20,   // Start at 70/20 pixels from the left and the top of the image (crop),
        50, 50,   // "Get" a `50 * 50` (w * h) area from the source image (crop),
        0, 0,     // Place the result at 0, 0 in the canvas,
        100, 100); // With as width / height: 100 * 100 (scale)
}
Image: <br/>
<img src="https://www.google.nl/images/srpr/logo3w.png" /><br/>
Canvas: <br/>
<canvas id="canvas" width="275px" height="95px"></canvas>