Browser tools

How to compress images online without losing quality

Open the AltFTool Image Compressor, add one or more JPG, PNG or WebP images, lower the quality slider until the before/after preview still looks right, optionally resize, then download each file or a ZIP. Compression runs in your browser, so images are not uploaded.

Updated 5 min read

On this page
  1. Compress an image step by step
  2. Why file size drops, and what you trade
  3. Your images stay on your device
  4. Related image jobs
  5. Related tools
  6. FAQ

Compress an image step by step

The Image Compressor handles single photos and whole batches. It works the same on desktop and mobile.

  1. Open the Image Compressor

    Go to /tools/all/image-compressor, or search 'compress image' with Ctrl+K.

  2. Add your images

    Drag images onto the page or choose them from your device. You can add several at once.

  3. Set the quality

    Move the quality slider down to shrink the file. The new size updates so you can see the saving.

  4. Resize if the image is oversized

    Turn on resize to cap the dimensions at the same time. A 4000-pixel camera photo rarely needs to be wider than about 1920 pixels for the web.

  5. Compare before and after

    Drag the before/after slider across the preview and look closely at detailed areas such as text, faces and gradients.

  6. Download

    Download each image, or download every result together as a ZIP file.

Why file size drops, and what you trade

Two things make an image file large: the number of pixels and how much detail the format keeps for each one. Resizing removes pixels; lowering quality lets the encoder discard detail your eye is unlikely to notice. Doing both usually gives the biggest saving.

JPEG-style compression is lossy, so some quality is always lost. The goal is to stop just before the loss becomes visible. Photos tolerate heavy compression well; screenshots, logos and images with sharp text show artefacts sooner, so keep the quality higher for those.

Your images stay on your device

Compression uses the browser's Canvas API inside your tab. The images are read, re-encoded and handed back to you as downloads without being sent to a server, which makes the tool suitable for personal photos and unpublished work. More on this in privacy and local processing.

All image tools are collected in the Image & Video category and the AltFLoveImg hub.

Tools used in this guide

Frequently asked questions

How do I compress an image to under 100 KB?

Resize the image to the smallest dimensions you need first, then lower the quality slider while watching the file size. Most photos reach 100 KB at around 1200 pixels wide with moderate quality.

Does compressing an image reduce its quality?

Lossy compression always removes some detail, but at sensible settings the difference is hard to see. Use the before/after slider to find the smallest size that still looks right.

Can I compress many images at once?

Yes. Add several images, compress them together and download all results in one ZIP file.

Are my images uploaded to AltFTool?

No. The Image Compressor runs in your browser using the Canvas API, so images never leave your device.

Keep reading

Image & Video toolsAltFLoveImg image hubExam photo and signature resizer