Image Canvas Resizer
Expand an image's canvas without stretching it — add letterbox bars, pillarbox bars, or a blurred background to fit any aspect ratio or fixed size. Perfect for social media posts, advertising creatives, and print assets. Everything runs in your browser; nothing is uploaded.
Drop images or a ZIP file here
Supports PNG, JPG, WebP, AVIF, GIF — drag multiple files or a .zip containing images
How to Resize an Image Canvas Online
Canvas resizing — sometimes called adding a letterbox or pillarbox — means expanding the frame around your image to meet a required aspect ratio or pixel size without distorting or cropping the original content. It is different from scaling: the image itself stays untouched, and only the empty space around it changes.
Step-by-Step Instructions
- Drop your images onto the upload area, click "Choose Files," or drag in a ZIP archive containing your images. Multiple formats are supported: PNG, JPG, WebP, AVIF, and GIF.
- Choose a canvas size. Pick an aspect ratio (like 1:1 for square), a standard social media size, an IAB advertising size, or enter fully custom pixel dimensions.
- Set the background. Transparent borders are great for PNGs and WebP. White or black give clean letterbox bars. The blurred background option blows up a copy of your image and blurs it to fill the empty space — popular for social media. Auto color samples the edge pixels of your image and fills with a matching solid color.
- Choose image position. Use the 3×3 grid to control whether your image snaps to a corner, an edge, or stays centered.
- Click Apply Settings to process. Previews appear below. You can change any option and click Apply again — no re-uploading needed.
- Download images individually or use "Download All as ZIP" for batch exports.
Background Fill Options
- Transparent — Available for PNG, WebP, and AVIF. The empty border area has no color — useful for compositing.
- White / Black — Clean, solid letterbox bars. Common for printing and formal presentations.
- Blurred image — The original image is scaled to fill the entire canvas and then blurred heavily, giving a colorful, contextually matched backdrop. Widely used for Instagram posts and YouTube thumbnails.
- Auto color — The tool samples pixels along the edges of your image and computes an average color, then fills the border with that color. Works best on images with a consistent background.
Proportional vs. Fixed Size
When you select a proportional ratio (e.g. 16:9), the output canvas is the smallest size at that ratio that fully contains your original image — no upscaling is applied. If your image is already 1920×1080, a 16:9 ratio canvas will stay 1920×1080.
When you pick a fixed size (social media or IAB preset, or custom), the image is scaled to fit inside that canvas while preserving its own aspect ratio. Borders are added to fill the rest.
Frequently Asked Questions
Why is my canvas-resized image larger than the original?
Adding a border naturally increases the overall pixel dimensions. If you pick a fixed size (e.g. 1200×628 for a Facebook post) that is larger than your source image, the image will be upscaled slightly to fit, and borders will be added. If you want zero upscaling, use the proportional ratio mode, which never enlarges the source.
Will using transparent background work in JPG files?
No — the JPG format does not support an alpha (transparency) channel. If you select JPG output and a transparent background, white will automatically be used instead. Switch to PNG, WebP, or AVIF to keep transparency.
Can I process an entire folder of images at once?
Yes. Pack your images into a ZIP file and drop that onto the upload area. The tool will extract all supported image files from the ZIP and process them with your current settings. You can also drag multiple individual image files at once.
What are IAB ad sizes?
The Interactive Advertising Bureau (IAB) publishes a standard set of ad unit dimensions that are widely accepted by publishers and ad networks — sizes like the Medium Rectangle (300×250), Leaderboard (728×90), and Half Page (300×600). This tool was originally built to make it easy to scale advertising creatives to every standard IAB size: you drop in a master asset and export every size at once, without distortion.
Does anything get uploaded to your servers?
Nothing. All image processing is performed locally in your browser using the HTML5 Canvas API. Your files never leave your device.
What is the maximum image size I can process?
There is no hard limit imposed by this tool, but very large images (above ~4000px on a side) may be slow depending on your device. Canvas dimensions for the output are capped at 4000px per side when using the custom size option. For custom IAB or social sizes that are smaller than the source, the image will be scaled down to fit.
Why would I use a blurred background instead of a solid color?
A blurred background (sometimes called "bokeh fill" or "focus fill") is visually engaging because it mirrors the colors and content of the image. It performs well on social media platforms like Instagram, where plain black or white letterboxing can feel stark. The blur intensity slider lets you go from barely-soft to fully abstract, giving you creative control.
I changed a setting but the previews didn't update automatically — is that a bug?
This is by design. Reprocessing all images on every keystroke would be slow for large batches, so settings changes are batched. Click the Apply Settings button whenever you want to reprocess the current images with the new options.
