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Resize image with javascript canvas (smoothly)

javascript
image-resizing
canvas
performance
Alex KataevbyAlex Kataev·Dec 25, 2024
TLDR

Resize an image smoothly using HTML canvas and JavaScript with the aid of the drawImage function and the imageSmoothingEnabled property. Here's a quick solution:

var canvas = document.createElement('canvas'); var ctx = canvas.getContext('2d'); // Don't forget to load your image image.onload = function() { // Your desired dimensions canvas.width = 100; // Yay to customization! Replace with your desired width canvas.height = 100; // Ditto for height ctx.imageSmoothingQuality = 'high'; ctx.imageSmoothingEnabled = true; // Smooth sailing? Think smooth scaling! ctx.drawImage(this, 0, 0, canvas.width, canvas.height); // Drawing power 💪 // Voilà, your resized image var smoothImage = canvas.toDataURL(); }; // Let's get that image going image.src = 'path/to/your/image.jpg'; // You know, that one picture...

Update canvas.width and canvas.height according to your requirements. Make sure imageSmoothingEnabled is set to true - it's the graphic designer's savior preventing jagged edges. Thus, a smoothly resized image all set!

Smooth resizing: The hows and whys

Interpolation: The magic behind the curtain

When you resize an image on a HTML <canvas>,
<small>(cue mysterious music🎵🎵 Mimimimimi... it's magical resize time!</small>)
the browser applies interpolation algorithms to create smoother transitions. This operation is called antialiasing, and it's all about preventing pixelated and jagged edges.

Higher-order interpolation methods

For higher-quality resizing, consider bilinear or bicubic interpolation. Bilinear interpolation is the friendly neighborhood algorithm that uses a 2x2 pixel box. But if you're feeling fancy, bicubic algorithm takes it up a notch using a 4x4 pixel grid for better smoothness.

Progressive downscaling: The step-master strategy

If you're dealing with large images, resizing in multiple steps is a good approach. It's common sense, really. You don't jump down all stairs at once, do you? Progressive downscaling or down-stepping is the same concept where you reduce the image size step by step to improve the final image quality.

Performance matters!

Your webpage isn't a sloth! Don't let high-quality image resizes turn it into one. Strike a balance between quality and performance: use faster algorithms, skip steps for minimal resize differences, and make your web application a speed demon!

Tips from the canvas resizing trenches

Keeping up appearances: Aspect Ratio

You wouldn't want your selfies distorted, right? Keep the aspect ratio constant when resizing to prevent image distortion. Just one simple division of original width by original height and presto, you have your aspect ratio!

Ensuring image is ready: Patience, my friend!

Image loading is like waiting for a bus. Don't draw or resize before it arrives i.e., before the image is fully loaded. Makes sense, doesn't it?

Canvas context: A world full of options

Dabble in the quality property in canvas's 2D context for improved resize results. Heard about the ctx.imageSmoothingQuality property? It's your secret ingredient to influence the bread and butter of resizing - image quality.

Building a timeless image resizing service

If you're in a love affair with Angular app (who isn't?), streamline your romantic escapades by implementing an image resizing service. Keep the function calls sweet, short, and sassy!