How to use Image Compressor
- 1Drop an image onto the page, or pick several to compress as a batch
- 2Leave Compression on Auto — the first file starts compressing as soon as it loads
- 3Switch to Quality for a manual slider, or Target size to aim at a specific KB figure
- 4Check the before and after sizes in the result panel
- 5Download the image, or the whole batch as a ZIP
What Image Compressor does
Most photographs carry far more data than anyone can see. A camera or phone writes a JPEG at a quality setting chosen to be safe rather than efficient, and a screenshot saved as PNG stores every one of its millions of possible colours even when the image only really uses a few hundred. Both leave a large amount of file size on the table for no visible benefit.
Compressing an image means finding the point where removing more data would finally start to show. That point is different for every image — a photo of foliage hides compression artefacts that would be obvious on a flat blue sky or a screenshot of text. Auto mode looks for that point per image rather than applying one fixed setting to everything.
When to use it
- Pages that load too slowly
- Images are usually the largest thing on a web page. Cutting a 4 MB hero photo to 300 KB changes load time far more than any amount of code tuning, and it is the change that moves Core Web Vitals.
- Attachments that bounce
- Mail servers commonly refuse anything over 20–25 MB. Target size mode lets you name a figure — 5000 KB for five photos under a 25 MB ceiling — instead of guessing at a quality slider and re-checking.
- Upload forms with a hard limit
- Passport photo, job application and government portals often cap a single file at 200 KB or 500 KB and reject anything larger without explaining by how much. Target size aims directly at the number they ask for.
- Screenshots for documentation
- A PNG screenshot of an interface typically uses a few hundred distinct colours. Reducing the palette usually halves the file with no visible change at all, because the original stored a 24-bit colour space it never used.
Image Compressor settings explained
- Auto
- Encodes the image repeatedly, comparing each attempt against the original with SSIM — a structural similarity measure that ignores changes the eye cannot see. Six bisection steps narrow in on the lowest quality that still looks the same, and the percentage match is reported with the result.
- Quality
- A direct slider from 20% to 100%, in 5% steps, starting at 80%. Use it when you want a predictable setting across many images rather than the best result for each one. It applies to JPEG, WebP and AVIF only.
- Target size (KB)
- Binary-searches the quality value to land just under the size you name, minimum 5 KB. It will not invent detail: if even the lowest quality cannot reach your target, you get the smallest achievable file rather than a failure.
- PNG handling
- PNG is lossless and has no quality dial, so the quality slider does nothing for it. Instead the palette is reduced with median-cut colour quantisation, which typically cuts 40–60% while keeping transparency intact.
Which mode to use
| Mode | You choose | Best for | Result size |
|---|---|---|---|
| Auto | Nothing | Almost everything | Smallest file that still looks identical |
| Quality | A quality % | Consistency across a batch | Varies by image |
| Target size | A KB figure | Hard upload limits | Just under your number |
Limits and what to expect
- 100 MB per file, 50 files per batch and 300 MB per queue.
- Images above roughly 100 megapixels are refused, because iOS Safari renders an oversized canvas blank rather than reporting an error.
- Files over 25 MB still work but are noticeably slower, since all the work happens on your own device.
- A file that is already well optimised is returned untouched rather than re-encoded — re-compressing a JPEG only adds artefacts.
- Animated GIFs are not supported here; only the first frame would survive.
Troubleshooting
- The file barely got smaller
- It was probably already compressed. Auto mode never returns a file larger than the original, so when there is nothing left to remove you get the original back with a note saying so. Re-compressing it again will not help.
- The quality slider does nothing
- The image is a PNG or another lossless format, where quality has no meaning. Colours are reduced instead. To use the slider, convert the image to JPEG or WebP first.
- Transparency turned into a black or white background
- JPEG cannot store transparency, so transparent pixels are flattened before encoding. Choose WebP or AVIF instead, or keep the image as a PNG, if the transparent background matters.
- A very large photo will not load
- Anything past about 100 megapixels exceeds what a browser canvas can handle reliably. Resize it down first, then compress the smaller version.
Your files and your privacy
The image is decoded, re-encoded and compared to the original entirely inside the browser tab, using the canvas API and your device's own CPU. No copy is uploaded, no temporary file is stored on a server, and nothing is queued for later processing. Closing the tab is all it takes to discard everything. The tool works with the network disconnected.
What to use next
FAQ
Does compressing an image reduce its quality?
For JPEG, WebP and AVIF, yes — they are lossy formats, so some data is always discarded. The question is whether you can see it. Auto mode uses SSIM to find the point just before the loss becomes visible, which is usually a 60–80% size reduction with no perceptible difference. PNG compression here is different: reducing the palette does change the image, but on screenshots and graphics the change is usually invisible.
What is the best format for a compressed image?
WebP is the safest modern default — it is smaller than JPEG at the same quality, supports transparency, and every current browser reads it. AVIF is smaller still but slower to encode. Keep JPEG when the file has to open in older software, and keep PNG when you need lossless pixels or transparency.
How do I compress an image to exactly 200 KB?
Choose Target size and enter 200. The tool binary-searches the quality value to land just under that figure. Aiming exactly at a hard cap is safer than guessing with the quality slider, because a JPEG's size does not change linearly with quality.
Can I compress several images at once?
Yes. Select or drop up to 50 files, within 300 MB in total, and each is compressed with the same settings. The finished images download together as a single ZIP.
Why did my PNG shrink less than a JPEG?
PNG is lossless, so the only way to shrink it is to store fewer distinct colours. Photographs contain thousands of subtly different shades and resist that; screenshots, logos and flat graphics have far fewer real colours and often halve in size. For a photograph, converting to JPEG or WebP will always beat compressing the PNG.
Is there a limit on how many images I can compress?
There is no daily cap, no account and no watermark. The only limits are per batch — 50 files, 100 MB each, 300 MB in total — and they exist to protect your browser tab, since the work runs on your device rather than a server.