Image Resizer

Resize images online without uploading them

Image resizing changes the pixel dimensions of a photo, illustration, screenshot, or other raster image. This browser-based image resizer uses the Canvas API, so the source file stays on your device while you choose exact width and height values.

How to resize an image

1. Select or drop an image file.
2. Review its original dimensions and file size.
3. Keep Lock aspect ratio enabled to prevent stretching, or choose independent resize for exact width and height control.
4. Set output dimensions up to 8,000 pixels.
5. Choose JPEG, PNG, or WebP. Adjust quality for JPEG and WebP.
6. Select Resize image, preview the result, and download it.

The original file remains unchanged. Each resize creates a separate output file.

Settings and trade-offs

Setting	What it controls	Best use
Width and height	Output pixel dimensions	Social media, documents, thumbnails
Lock aspect ratio	Keeps original proportions	Photos and illustrations
Independent resize	Allows different width and height	Deliberate stretching or fixed layouts
PNG	Lossless encoding with transparency	Logos, screenshots, graphics
JPEG	Lossy encoding with quality control	Photographs and smaller files
WebP	Modern lossy encoding with quality control	Web pages and compact downloads

Aspect ratio and image quality

An aspect ratio is the relationship between an image's width and height. Changing only one dimension while keeping the ratio locked calculates the other dimension automatically. This prevents circles becoming ovals and faces becoming distorted.

Downscaling generally looks sharp and often reduces file size. Upscaling creates additional pixels but cannot restore detail that was not present in the source. For important print work or substantial enlargement, dedicated resampling software may provide better results.

Format and quality guidance

PNG preserves transparency and ignores the quality slider. JPEG removes transparency and is usually the smallest choice for photographic content. WebP often provides a useful balance between visual quality and file size, but compatibility should be considered when sharing files with older software.

The quality value affects JPEG and WebP encoding, not the image dimensions. Lower values create smaller files with more visible compression; higher values preserve more detail at the cost of file size.

Canvas implementation

The browser draws the source image into a canvas sized to the requested output, then encodes that canvas in the selected format.

const canvas = document.createElement("canvas");
canvas.width = outputWidth;
canvas.height = outputHeight;

const context = canvas.getContext("2d");
context.drawImage(image, 0, 0, outputWidth, outputHeight);
canvas.toBlob((blob) => {
  // Download or preview blob
}, "image/webp", quality / 100);

Equivalent resizing with Python and Pillow:

from PIL import Image

with Image.open("source.jpg") as image:
    resized = image.resize((1200, 800))
    resized.save("resized.webp", quality=90)

Equivalent command-line resizing with ImageMagick:

magick source.jpg -resize 1200x800\> -quality 90 resized.jpg

Privacy and limits

Files are processed locally with the Canvas API; no upload or server-side conversion is required. Browser memory limits still apply to very large images, and the maximum output width or height is 8,000 pixels.

Transparent source images should be exported as PNG when transparency matters. JPEG output cannot retain an alpha channel.