Image Compressor

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 level you control, so you decide how much detail to trade for a smaller file.

The number that matters is right in front of you. Move the quality slider and the tool re-compresses on the spot, showing the original size, the compressed size, and how much you saved — so you can 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 quality slider, the canvas is re-encoded as a JPEG at that quality 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 the result against your original file so the trade-off is never a guess, 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, never uploaded.
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; original vs new size and percent saved update live.
5. Step 5. Download the result, saved as your filename with -compressed.jpg appended.

Privacy

Compression happens entirely on your device. The image is read straight from disk, drawn and re-encoded in the page's memory, and the JPEG is produced locally — no copy is uploaded to NineClip or anyone else.

There is no account and nothing is stored. Close the tab and both images are gone from memory, which makes it safe for personal photos and anything you would rather not hand to a server.

Technical Details

Standards & 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 & Limitations

Compression is lossy and one-directional. At 80% most photos look indistinguishable from the original at a fraction of the size; push the slider low and you start to see blocking and soft edges. The live size readout is there so you can find the point where it still looks right to you.

It always outputs JPEG, so transparency is not preserved. Because the tool does not paint a background first, transparent areas come out as a solid colour (black in most browsers) — so this is built for photographs, not logos or cut-outs. To keep transparency, compress to WebP or keep PNG.

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

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

Real-World Use Cases

When to use it — and when not to

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

Frequently Asked Questions

References

• HTMLCanvasElement: toBlob() — MDN
• The JPEG standard, ISO/IEC 10918 (ANSI)
• Image file type and format guide — MDN

Related Tools