Image Compressor

About the Image Compressor

This free image compressor reduces the file size of a JPG, PNG or WebP. Move the quality slider, watch the new size appear immediately, and download when it looks right.

Everything runs in your browser — your images are never uploaded to a server.

How lossy compression actually works

It helps to know what the slider is throwing away, because then you can tell where it will show.

Compression exploits the fact that the human eye is not a measuring instrument. It is very good at seeing edges and brightness, and comparatively poor at seeing fine colour detail. So a lossy encoder keeps the information you notice and discards the information you do not.

Two of its main tricks:

Colour is stored at lower resolution than brightness. Chroma subsampling keeps full detail in the light-and-dark channel and halves the colour detail — a saving of a third before anything else happens, and almost invisible on a photograph.

Fine detail is rounded off. The image is broken into blocks and each is described as a combination of patterns, from broad shapes to fine texture. The fine-texture coefficients get rounded hard, and many round to zero. The quality slider is essentially setting how hard that rounding is.

This explains exactly where artefacts appear first: smooth gradients and sharp edges. A clear sky turns into faint bands or blotches, and text picks up a grey mist around the letters, long before a busy patch of grass or gravel shows any damage at all.

Choosing a quality setting

• 90–100 — barely any saving over the original for most photographs. Use only when the image will be edited or enlarged later.
• 80–85 — the sweet spot. Large saving, no visible change at normal viewing size. Start here.
• 70–80 — still good for thumbnails, background images and anything small on the page.
• 50–70 — visible on photographs, especially in skies. Acceptable for a heavily blurred background.
• Below 50 — clearly degraded. Rarely worth it.

Judge the result at the size it will be displayed, not zoomed to 400%. Artefacts invisible at normal size are glaring at high magnification, and nobody views your page at 400%.

Resize first — it is the bigger lever

The most common mistake is compressing a huge image instead of making it smaller.

File size follows the pixel count, which follows area. A 4000 × 3000 photo has twelve million pixels. Resized to 1200 × 900 it has about one million — 92% fewer. No quality slider can achieve that without wrecking the image.

So the order that works is:

1. Resize to the largest size it will actually be displayed at
2. Then compress at quality 80–85
3. Then consider WebP if it is still too heavy

A 4 MB photo run through those steps typically lands under 150 KB and looks identical on the page. Use Image Resizer for the first step.

Why PNG behaves differently

PNG is lossless — it cannot discard detail the way JPG does, so there is no quality slider in the normal sense.

Compressing a PNG means reducing the number of colours it stores. A PNG with a 256-colour palette is far smaller than one with sixteen million, and on a logo, icon or flat illustration the difference is often invisible because the image only ever used a handful of colours.

On a photograph, it shows badly. Reducing a photo to 256 colours produces visible banding and speckle. This is the tool telling you something useful: a photograph should not be a PNG at all. Convert it to JPG or WebP and you will get a far smaller file that looks better.

The rule: PNG for logos, screenshots, diagrams and transparency. JPG or WebP for photographs.

When the file gets bigger instead of smaller

It happens, and it is not a fault.

The image was already compressed hard. Re-encoding an image that has been through a heavy pass already cannot help, and the new encoder's overhead can tip it over.

A photograph was saved as PNG. Compressing to PNG again keeps it lossless and large. Change the format.

The image is tiny. Below a few kilobytes, format headers dominate and there is nothing left to squeeze.

The quality is set very high. At 95 or above you may be asking for more fidelity than the original had.

If the result is bigger, keep the original — the tool shows you both sizes so you can tell.

How to use it

• Upload an image — click the upload area or drag and drop a JPG, PNG or WebP
• Adjust quality — lower quality means a smaller file; watch the size update
• Pick a format (optional) — keep the original, or convert to JPG/WebP for more savings
• Download — save your compressed image

Good to know

• Keep your originals. Compression is permanent; the discarded detail cannot be recovered.
• Never compress an already-compressed copy. Go back to the original each time. Repeated passes compound the damage.
• WebP usually beats JPG by 25–35% at the same visible quality, and every current browser supports it.
• Check gradients, not detail. Skies, studio backdrops and skin tones show artefacts first.
• Text in an image suffers badly. For screenshots containing text, use PNG or a high quality setting.
• EXIF data is usually dropped, including GPS coordinates — good for privacy, worth knowing if you wanted the camera information.
• Compressing many images? Use Bulk Image Resizer rather than repeating this by hand.

Common questions

How much can I compress an image without losing quality?

Some loss is unavoidable with JPG and WebP, but at quality 80–85 it is not visible at normal viewing size, and the saving is usually 60–80% against an uncompressed original. Judge the result at the size it will actually be displayed rather than zoomed in, since artefacts invisible on the page are obvious at 400%.

Why did my image get bigger after compressing?

Usually because it was already compressed hard, so there is nothing left to remove and the new encoder's overhead tips the balance. It also happens with very small images, where format headers dominate, and with photographs saved as PNG, which stays lossless and large. The tool shows both sizes so you can simply keep whichever is smaller.

Should I resize or compress?

Resize first, then compress — resizing is by far the bigger lever. File size follows pixel area, so halving both dimensions removes three quarters of the pixels. A 4000-pixel photo resized to 1200 and then compressed at quality 82 typically drops from several megabytes to well under 150 KB while looking identical on the page.

Why doesn't PNG compression work as well?

Because PNG is lossless and cannot discard detail. Compressing a PNG reduces the number of colours it stores, which works beautifully on logos, icons and flat illustrations but produces visible banding on a photograph. If your PNG is a photograph, the real fix is to convert it to JPG or WebP rather than compress it further.

Which format gives the smallest file?

For photographs, WebP — typically 25–35% smaller than JPG at the same visual quality, with support in every current browser. AVIF is smaller again but encodes slowly. For logos, diagrams and anything with transparency or text, lossless WebP or PNG. JPG remains the safest choice for compatibility with older software and upload forms.

Will compressing remove the photo's location data?

Usually yes. Re-encoding normally drops EXIF metadata, including GPS coordinates, camera model and timestamp. That is convenient for privacy when sharing a photo, and inconvenient if you wanted the information kept. To check what an image is carrying before you share it, use the Image Metadata Viewer.

Are my images uploaded to a server?

No. Your browser decodes the image, re-encodes it at the quality you chose, and hands the result back — all on your own device. Nothing is transmitted or stored, and the tool works with your connection switched off.

Related tools

• Image Resizer — do this first; it saves far more than compression alone
• Compress Image to Size — hit an exact file size target
• Bulk Image Resizer — process a whole folder at once
• Image Metadata Viewer — see what information a photo carries