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Resize images using client-side canvas processing
Resize images instantly with our free online image resizer tool. This tool helps designers and web developers resize images to specific dimensions or percentages while maintaining aspect ratio. Simply upload your image, set dimensions, and get resized output in real-time.
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Upload an image to resize it
This tool resizes images client-side using HTML5 Canvas. All processing happens in your browser - no images are uploaded to any server.
Tips:
Image resize tool scales images to new dimensions while maintaining quality. This is essential for creating thumbnails, optimizing images for web, fitting images into specific layouts, or reducing file size for faster loading.
The tool loads the image, calculates new dimensions based on specified width/height (optionally maintaining aspect ratio), and resamples the image using interpolation algorithms. Quality settings control the compression of the output file.
Resampling algorithms: Nearest-neighbor (fastest, pixelated), Bilinear (smooth, fast), Bicubic (sharper, slower), Lanczos (highest quality, slowest). For downscaling, quality matters less; for upscaling, algorithm choice is critical. Canvas-based resize uses browser's built-in bilinear.
Create small preview images from originals.
1920x1080 → 300x169 thumbnailResize large images for faster page loading.
Resize images to platform-specific dimensions.
Resize user uploads to standard avatar sizes.
Generate multiple sizes for srcset.
function resizeImage(file, maxWidth, maxHeight) {
return new Promise((resolve) => {
const img = new Image();
img.onload = () => {
// Calculate new dimensions
let { width, height } = img;
if (width > maxWidth) {
height = height * (maxWidth / width);
width = maxWidth;
}
if (height > maxHeight) {
width = width * (maxHeight / height);
height = maxHeight;
}
// Draw to canvas
const canvas = document.createElement('canvas');
canvas.width = width;
canvas.height = height;
const ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0, width, height);
// Get result
canvas.toBlob(resolve, 'image/jpeg', 0.85);
};
img.src = URL.createObjectURL(file);
});
}Canvas-based resize with aspect ratio preservation. Quality 0.85 balances size and quality.
from PIL import Image
def resize_image(input_path, output_path, size, maintain_aspect=True):
with Image.open(input_path) as img:
if maintain_aspect:
img.thumbnail(size, Image.Resampling.LANCZOS)
else:
img = img.resize(size, Image.Resampling.LANCZOS)
img.save(output_path, optimize=True, quality=85)
# Resize to fit within 800x600
resize_image('photo.jpg', 'photo_small.jpg', (800, 600))
# Generate multiple sizes
sizes = {'small': (300, 300), 'medium': (600, 600), 'large': (1200, 1200)}
for name, size in sizes.items():
resize_image('original.jpg', f'{name}.jpg', size)Pillow's thumbnail() maintains aspect ratio. LANCZOS provides high quality. optimize=True reduces file size.
Use image resize for thumbnail generation, web optimization, social media formatting, avatar processing, or anytime you need images at specific dimensions.
Specify only width or height, calculate the other proportionally: newHeight = originalHeight * (newWidth / originalWidth). Or use "contain" mode to fit within a box while preserving ratio.
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