NineClip Free Tools

Image Compressor

Compress an image to JPEG with a quality slider and watch the file size drop as you drag, in your browser.

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Quick answer

Image Compressor re-encodes your image as a JPEG at a quality you choose, from 10% to 100% with 80% as the default, in your browser. As you drag the slider it shows the original size, the new size and the percent saved, so you can see what each step costs in quality and saves in bytes. It accepts JPG, PNG and WebP and always outputs a JPEG. Your image is not uploaded.

  • 10–100%quality range
  • 80%default quality
  • 3input formats: JPG, PNG, WebP
  • 0files uploaded

What the Image Compressor does

Photos straight off a phone or camera are often several megabytes, more than you need for email, a website or a form with a size limit. This tool shrinks them by re-saving as a JPEG at a quality you control, so you decide how much detail to give up for a smaller file.

Move the quality slider and the tool re-compresses on the spot, showing the original size, the compressed size and how much you saved. Stop at the smallest file that still looks good to you.

How it works

Your image is drawn onto an HTML5 canvas at its full dimensions. Each time you move the slider, the canvas is re-encoded as a JPEG at that setting: the slider's percentage becomes the encoder's 0-to-1 quality value.

JPEG compression is lossy. It discards detail your eye is least likely to notice, and lower quality means a smaller file with more of that loss. The tool measures each result against your original file, and the download is named after your file with -compressed.jpg appended.

Processing pipeline

  1. Step 1. Drop in a JPG, PNG or WebP image. It is decoded locally.
  2. Step 2. The image is drawn to a canvas at full size.
  3. Step 3. Pick a quality from 10% to 100% (80% is the default).
  4. Step 4. The canvas is re-encoded as a JPEG at that quality, and the original size, new size and percent saved update as you go.
  5. Step 5. Download the result, saved as your filename with -compressed.jpg appended.

What the quality slider trades

80% defaultmost photos look the same10%100%◀ smaller file, blockingbigger file ▶
Lower quality gives a smaller file and more visible damage. Start at the 80% default and watch the size readout before you go lower.

Privacy

Compression runs on your device. The image is read from disk, drawn and re-encoded in the page's memory, and the JPEG is produced locally, so NineClip never receives a copy.

No account is involved and the page keeps nothing once you close the tab, so personal photos you would rather not hand to a server are safe to compress here.

Technical details

EngineHTML5 Canvas (browser-native)
AcceptsJPG, PNG, WebP
OutputJPEG (.jpg)
Quality10-100% slider (default 80%)
FeedbackOriginal vs compressed size and % saved, updated as you drag
TransparencyNot kept (JPEG); transparent areas turn solid
UploadNone; compression runs in your browser

Standards and references

  • ISO/IEC 10918 (JPEG): the lossy compression standard used here: 8x8 DCT blocks, no transparency. Lower quality discards more high-frequency detail for a smaller file.
  • HTML Canvas API: toBlob('image/jpeg', q) does the encoding, where q is the slider value from 0.10 to 1.00.

Accuracy and limits

Compression is lossy and cannot be undone. At 80% most photos look the same as the original at a fraction of the size; push the slider low and you start to see blocking and soft edges. Watch the size readout to find the point where it still looks right to you.

It always outputs JPEG, so transparency is lost. The tool does not paint a background first, so transparent areas come out as a solid colour (black in most browsers). Use it for photographs, not logos or cut-outs; to keep transparency, compress to WebP or keep the PNG.

Re-compressing an already-compressed JPEG stacks the loss, since each save throws away a little more (generation loss). Compress once, from the highest-quality original you have.

Dimensions stay the same; this tool changes quality, not size. If the image is also larger than you need in pixels, resize it first and then compress. Fewer pixels plus JPEG compression gives the smallest file.

Resize first, then compress

OriginalResizefewer pixelsJPGCompresssmallest file
Fewer pixels plus JPEG compression gives the smallest file. Compress once, from the best original you have.

Real-world uses

Email and uploads

Get a heavy photo under an attachment or form size limit without obvious quality loss.

Faster web pages

Shrink photos so pages load quicker, setting the quality to taste.

Free up space

Compress a batch of photos to reclaim storage.

Share quickly

Send smaller files over chat or a slow connection.

When it fits, and when it doesn't

Good for

  • Photographs and detailed images
  • Choosing your own balance of size and quality
  • Getting under an upload limit
  • JPG, PNG or WebP photos

Not the best choice for

  • Logos, icons, or anything needing transparency
  • Keeping the image pixel-perfect (it is lossy)
  • Changing pixel dimensions (use a resizer)
  • Repeatedly re-compressing the same JPEG

Need transparency or lossless? Keep PNG or convert to WebP. Need fewer pixels? Resize first, then compress.

Tips and tricks

What we would do

Frequently asked questions

What quality should I choose?
Start at the 80% default, where most photos look the same as the original. Drag lower while watching the size and preview, and stop at the smallest file that still looks good to you.
Does compressing lose quality?
Yes. JPEG is lossy, so some detail is discarded, and lower quality discards more. At 80% the loss is usually invisible on photos; very low settings show blocking and soft edges.
What formats can I compress?
JPG, PNG and WebP go in. A JPEG always comes out, saved with -compressed.jpg appended to your filename.
Will it keep transparency?
No. JPEG has no transparency, and the tool does not add a background, so transparent areas come out solid (black in most browsers). For transparent images, keep PNG or compress to WebP instead.
Are my images uploaded?
No. Everything runs on an HTML5 canvas in your browser. Nothing goes to a server, and refreshing the page clears it from memory.
Does it make the image smaller in pixels?
No, it changes quality, not dimensions. To reduce the pixel size too, resize the image first and then compress; that gives the smallest file.
Why did my already-small image barely shrink?
If it is already a compressed JPEG, there is little left to remove, and re-compressing mainly adds loss. Compression helps most on large, high-quality originals.
Can I compress the same photo twice to make it smaller?
You can, but each pass throws away more detail (generation loss) for diminishing size gains. It is better to compress once from the best original.
Is my original file changed?
No. A new compressed JPEG is created and your original is left untouched.
Does it work on a phone?
Yes, in any modern mobile browser. Very large images use more memory while encoding.

References

Written from the tool's quality-slider code: it always saves a JPEG, reports the size after each change, and turns transparent areas solid.

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Back to the Image Compressor

Your file is processed on this device and never uploaded, and there's no account to create.

Go to the tool Explore Image Tools