thecompressjpeg

Does compressing an image reduce its quality?

Lossless compression does not touch quality at all. Lossy compression always reduces it — the useful question is whether the reduction is visible, and at sensible settings it is not.

The direct answer

Lossless (PNG, lossless WebP)
No. Every pixel value is identical afterwards.
Lossy (JPEG, WebP, AVIF)
Yes, always. Detail is discarded permanently.
Is it visible?
At quality 75–85 on a photograph, essentially never at normal viewing size.
Where it becomes visible
Below about 70 on smooth gradients; at any quality on text and line art.
Resizing
A separate loss, and usually a much larger one — but also usually invisible if sized correctly.
Reversible?
Lossless yes, lossy never. Keep your original.

What actually changes

Two different questions

"Does compression reduce quality" conflates two things: whether information is discarded, and whether you can see that it was.

Information: lossless formats discard none, lossy formats always discard some. That part is absolute and not a matter of settings.

Visibility: a completely different question, decided by how much was discarded, what the image contains, and how large it is displayed. A photograph at quality 80 has genuinely lost data and genuinely looks identical at the size anyone will view it.

Most arguments about this are people answering different questions.

Where the visible threshold sits

Quality 90–100
No visible difference under any inspection. Also very little size saving — this range is mostly wasted.
Quality 80–90
Differences findable at 200–400% zoom in flat areas. Invisible at display size.
Quality 70–80
The practical range. Slight softening in smooth gradients if you look for it.
Quality 60–70
Visible softening in sky, skin and out-of-focus areas without looking for it.
Below 60
Obvious blocking, ringing and banding.

These are for photographic content. For text, screenshots and line art there is no safe range — lossy encoding produces visible haloes at every quality, and the answer is to change format rather than settings.

Content moves the threshold more than the setting does

Texture hides compression; smoothness exposes it.

A photograph of foliage, gravel or a knitted jumper has fine irregular detail everywhere, which masks the encoder's approximations. The same quality setting on a clear blue sky or a studio backdrop can show visible banding, because there is nothing for the artefacts to hide behind.

This is why one image survives quality 70 and another needs 85. Judge the result rather than trusting a number.

Resizing is the bigger loss, and usually the right one

Reducing an image from 4000 pixels wide to 1600 discards 84% of its pixels — far more information than any quality setting removes. Yet if the image is displayed in an 800-pixel column, none of it was ever going to be seen.

This is the key insight about "quality loss" on the web: discarding data nobody can perceive is not a cost. Serving 4000 pixels into an 800-pixel space is not higher quality, it is just more bytes.

How to judge it properly

Look at the compressed image at the size it will actually be displayed, beside the original, at the same scale. Zooming to 400% tells you what an encoder did; it does not tell you what a reader will see, and optimising against it wastes bytes on nobody's behalf.

Then look deliberately at the places artefacts appear first: large flat areas, gradients, skin tones, and any hard boundary between contrasting colours. If those are clean, the image is clean.

Try it yourself

Everything below runs in your browser, so you can test any of this on your own files without uploading them.

  • Compress JPEG

    Shrink JPG and JPEG photographs with a quality slider or an exact target size.

    Open the tool

  • Lossless compressor

    Zero quality loss, every pixel preserved exactly. Honest about how modest the saving is.

    Open the tool

  • Compress PNG

    Lossless by default, with transparency carried through untouched.

    Open the tool

Questions

Frequently asked questions

Every answer below is present in the page source, expanded, so it can be read without opening anything.

Does compressing a photo always lose quality?

If you use a lossy format such as JPEG or WebP, yes — data is discarded by design. If you use a lossless format such as PNG or lossless WebP, no data is lost at all. The saving is much smaller in the lossless case, which is the trade.

How much quality do I lose at quality 80?

Measurably some, visibly none for a photograph at normal viewing size. You would have to zoom to 200–400% and study flat areas such as sky or skin to find the differences. That is why 80 is the standard recommendation.

Can I compress without losing any quality at all?

Yes — use PNG or lossless WebP, which discard nothing. Expect a much larger file, particularly for photographs, where lossless compression has almost no redundancy to exploit.

Does resizing reduce quality?

It discards pixels permanently, so technically yes, and far more of them than compression does. But if the image is displayed smaller than its original dimensions, those pixels were never visible. Serving more pixels than the layout can show is not quality, it is waste.

Why does my screenshot look bad even at high quality?

Because it is the wrong format, not the wrong setting. JPEG produces ringing around every hard edge and smears coloured text through chroma subsampling, at every quality level. Save screenshots as PNG or lossless WebP and the problem disappears entirely.

Can I get the quality back afterwards?

No. Lossy compression is one-way — the discarded detail is not stored anywhere and cannot be reconstructed. Saving a compressed JPEG as PNG gives you a large, faithful copy of the degraded image, not the original. Always keep your originals.

From the blog

Related reading

Longer, more practical guides from the blog.

  • Image Compression

    JPEG Quality Settings Explained: What the Number Actually Means

    Quality 80 is not 80% of anything. It is an index into a quantisation table. Measured on one photograph: dropping from 100 to 90 removes 77% of the file and 4.2 dB of fidelity; dropping from 40 to 30 removes 17% and costs almost as much.

    8 min read

  • Image Formats

    PNG vs JPEG: When to Use Each, With the File Sizes to Prove It

    PNG stored the same photograph in 1274.1 KB where JPEG needed 67.5 KB — nineteen times larger. On a flat graphic PNG won. On a smooth gradient PNG lost to JPEG by a factor of two, which surprises most people.

    9 min read

  • Practical Guides

    How to Compress Images for a Website Without Wrecking Them

    Resize before you compress. Measured on one photograph: half the width at quality 80 produced a 16.4 KB file, while full width at quality 40 produced 20.6 KB and looked far worse. The order of operations matters more than the settings.

    8 min read