画像圧縮オンライン

What this image compressor does

This tool takes an image you upload and re-encodes it so the file uses fewer bytes. Compressing an image is different from resizing it: resizing changes the width and height in pixels, while compression reduces image file size and usually leaves the dimensions untouched. A photo can stay 4000 × 3000 pixels and still lose most of its weight, or barely shrink at all if it was already optimized.

Use it when a JPEG is too big for a website upload form, an email attachment limit, a social platform, or a product listing. If you also need different dimensions, run the image resizer first and compress afterwards.

Three ways to reduce image size

File size comes from three things: how much detail the encoder keeps, how many pixels the image has, and which format stores those pixels. You can pull any of those levers, and combining them gives the biggest reduction.

1. Lower the encoding quality

The quickest way to reduce image file size is to compress at a lower quality. Dropping a photo from 100% to 80% often removes more than half the bytes with no obvious difference on screen. This is what the quality slider above does.

2. Reduce the pixel dimensions

A 6000-pixel-wide photo displayed in a 1200-pixel column is carrying five times more data than it needs. Cutting the width in half removes roughly three quarters of the pixels. Use the resize image tool to set exact dimensions or a percentage, then compress the result.

3. Switch to a lighter format

Format matters as much as quality. A screenshot saved as PNG can shrink dramatically as WEBP, and a photo stored as PNG is often much smaller as JPEG. Keep PNG only when you need transparency or pixel-exact graphics.

Compressing JPEG, PNG, WEBP, and HEIC

Compress JPEG

JPEG is built for photographs and responds well to compression. Camera and phone JPEGs are usually saved at a very high quality setting, so re-encoding at 75–85% typically cuts the file size in half while the photo still looks the same at normal viewing size.

Compress PNG

PNG is lossless. This compressor runs OxiPNG in your browser on the original PNG bytes — it does not re-encode through Canvas. Flat graphics, logos, and screenshots compress well. Photographs saved as PNG usually get much smaller by converting them instead.

Compress WEBP and AVIF

WEBP and AVIF are already efficient modern formats, so expect smaller gains than with an untouched JPEG. They are still worth compressing when you are chasing page speed and every kilobyte in the payload counts.

Compress HEIC photos from an iPhone

HEIC uploads are compressed and saved as JPEG, which makes them viewable everywhere. If you only need the format change without extra compression, use the dedicated HEIC to JPG converter.

Why people reduce image file size

• Faster pages. Images are usually the heaviest part of a page, so compressing them is the simplest way to improve load time and Core Web Vitals.
• Email and messaging limits. Most providers cap attachments, and a handful of phone photos passes that cap quickly.
• Upload forms. Job applications, government portals, and school systems often reject anything over a fixed number of kilobytes.
• Marketplace and CMS rules. Storefronts and content platforms enforce their own maximum file size per image.
• Storage and backups. Smaller files mean more photos in the same space and quicker syncing.

Supported formats and limits

Accepted uploads: JPEG, PNG, WEBP, GIF, BMP, TIFF, AVIF, HEIC. Maximum size: 200 MB per image.

Limitations: Compression can reduce visual quality. HEIC inputs are saved as JPEG. Transparent PNGs converted through JPEG-oriented paths lose transparency. Savings depend on the original file.

Privacy: Your image is processed locally in your browser and is not uploaded to ImgTask's server. Image files never leave your device. No account is needed and results carry no watermark.