Image Compressor Online Free
Reduce image file size up to 90% without visible quality loss. Supports JPG, PNG, WebP. Runs in your browser, no upload, no watermark.
What the quality slider is actually doing to your pixels
Every compression here runs through one browser API: canvas.toBlob(callback, mimeType, quality). The image is drawn onto an offscreen canvas at full resolution, then re-encoded through that call with a quality value from 0 to 1. No image ever leaves your device, there’s no server doing the recompression, the browser’s own JPEG or WebP encoder does the work exactly as it would for any other canvas export.
Batch compression flow
Image object; its natural width and height are read once so the canvas can be sized exactly to match, no scaling happens during compression by default.
drawImage(img, 0, 0), which is a plain 1:1 pixel copy, no resampling filter is applied at this stage.
toBlob() at the chosen MIME type and quality. This is where the actual size reduction happens, the browser’s native encoder discards data according to the format’s own compression algorithm.
Target size mode doesn’t guess a quality value once, it bisects the 5-95 quality range up to ten times, reencoding the canvas at each midpoint until it converges on the highest quality that still fits under your KB target. This is standard binary search applied to a monotonic relationship: higher quality almost always means larger file size for JPEG and WebP.
Why PNG behaves differently
| Format | Compression type | Quality parameter |
|---|---|---|
| JPEG | Lossy, DCT-based | 0-100, directly controls detail loss |
| WebP | Lossy by default | 0-100, generally smaller than JPEG at equal quality |
| PNG | Lossless, DEFLATE | Ignored by browsers, always maximum compression |
image/png because PNG is a lossless format, there’s no continuous quality dial, only how efficiently the same pixels get packed. The tool disables the quality slider automatically when PNG is selected for exactly this reason, and target-size mode is skipped for PNG since there’s nothing to bisect.Quality hints
The label under the slider, from near lossless down to visible loss, maps directly to fixed quality bands and is purely informational text, not a separate calculation.
Presets
Web (JPEG, quality 80), max compression (JPEG, 50), lossless (PNG), WebP (75), and thumbnail (JPEG, 60) are just pre-filled format and quality combinations, not distinct algorithms.
Batch summary
Total original size, total compressed size, and overall percentage saved are simple sums and a ratio across every file processed in one run.
- HTMLCanvasElement.toBlob(), the API doing the actual re-encoding.
- MDN image format guide, comparing JPEG, PNG, and WebP compression characteristics.
- WebP documentation from Google, the team that developed the format.
When file size decides
Shrinking a batch of product photos before uploading to an online store, hitting a strict attachment size limit for an email, preparing images for a page speed audit where every kilobyte counts toward load time, converting a folder of PNG screenshots to WebP for a blog post, or getting a camera photo under a forum’s upload cap using the target size mode instead of guessing at a quality percentage.
FAQ: Image Compressor Online Free
No. All compression happens locally in your browser. Your images are never sent to any server. This makes the image compressor online free completely private, with no data retention and no risk of files leaking.
Set quality to 80-90% for JPG or WebP. At these levels most people cannot see a visual difference, but file size drops by 40-70%. For PNG, use the PNG option which is lossless. Converting a PNG to WebP at 80% quality often cuts the file in half with no visible change.
Enable the Target file size option and type your target in KB. The tool runs a binary search across quality levels to get as close to that number as possible. It works best for JPG and WebP. PNG is lossless so the exact target size cannot always be reached.
JPG uses lossy compression — great for photos, handles quality reduction well. PNG is lossless and ideal for graphics with text or transparency, though file sizes are larger. WebP is a modern format that achieves better compression than both JPG and PNG while maintaining quality. Converting to WebP is the fastest way to reduce image size for websites.
Yes. Upload up to 50 images at once. All files are compressed with the same settings. The results panel shows before and after size for each image, and you can download them all at once.
This can happen when the original file was already well-optimised, or when you set quality higher than the original encoding. It also happens if you convert a small JPG to PNG. In these cases, keep the original format and lower quality slightly. Converting to WebP usually avoids this.
It depends on the original file and format. A typical uncompressed photo can shrink 60-80% as JPG at 80% quality with no noticeable visual difference. Converting to WebP often saves another 25-40% on top of that. PNGs with large areas of flat colour compress well; complex photographic PNGs compress less. The tool shows the exact savings per file after processing.
From the blog
Notes on images and colour
Format choices, compression tradeoffs and accessible palettes.
