How to Compress an Image Without Losing Quality

Compressing an image always changes the file in some way — the question is whether that change is visible. Done properly, you can cut a photo's file size by 60-90% without anyone noticing a difference on screen. Done badly, you get blocky faces, muddy gradients, and fuzzy text. The difference comes down to understanding what kind of compression you're using and picking settings that match the image, not just accepting whatever default a tool gives you.

Understanding lossy vs lossless compression

There are two fundamentally different approaches, and mixing them up is the main reason people end up disappointed.

Lossy compression (used by JPEG and most WebP settings) throws away data the human eye is unlikely to notice — subtle colour transitions, high-frequency detail in busy areas. At quality settings above roughly 75-80%, this loss is genuinely invisible on a screen or in print. Push it below 50% and you'll start seeing blocky artefacts around edges.

Lossless compression (used by PNG, and optionally by WebP) rearranges and packs data more efficiently without discarding anything. The image comes out pixel-for-pixel identical, but the size reduction is smaller — typically 10-40% rather than 70-90%.

Knowing which category your image needs is the first real decision, not the compression tool itself.

How to compress an image but keep the quality

Follow this order and you'll almost always land on a file that looks identical to the original but weighs a fraction as much.

1. Identify the image type. Photos with lots of colour variation (portraits, landscapes, product shots) compress well as JPEG or WebP. Screenshots, logos, diagrams, and anything with flat colour or text should stay PNG or become WebP with lossless mode — JPEG will introduce ugly ringing artefacts around sharp edges and text.
2. Resize before you compress. If the image is going on a web page at 800px wide but you're uploading a 4000px camera original, resizing first does more for file size than any compression setting ever will. A 4000×3000 photo resized to 1200×900 is already roughly 90% smaller before compression even starts.
3. Set quality between 75-85% for JPEG. This is the sweet spot where file size drops sharply but visible detail barely changes. Below 60%, degradation becomes noticeable in skies, skin tones, and shadows — the areas where smooth gradients live.
4. Avoid repeated re-saving. Every time you open a JPEG, edit it, and re-save as JPEG, you lose a little more quality — this is cumulative, not a one-off cost. If you need to edit further, keep a lossless master copy (PNG or the original RAW/TIFF) and only export to JPEG once, at the end.
5. Check the result at 100% zoom, not just as a thumbnail. Artefacts that are invisible when scaled down can be obvious at full size, particularly around text or fine lines.

Can you reduce PNG size without losing quality?

Yes, and this is one of the more underused tricks. PNG files are lossless by design, but the encoding of that lossless data can be wildly inefficient depending on what software created the file. Screenshots taken on Windows or macOS, for instance, often carry redundant metadata and unoptimised colour palettes.

Tools that re-encode PNGs (rather than just recompressing them) can shrink a file by 30-50% with zero pixel change, by:

• Reducing the colour palette to only the colours actually used (an 8-bit indexed PNG with 200 colours is far smaller than one assuming 16 million possible colours it never uses)
• Stripping unnecessary metadata chunks (colour profiles, text comments, thumbnail previews)
• Using better internal compression algorithms (this is what tools like pngcrush, oxipng, and most browser-based PNG optimisers do under the hood)

So the honest answer is: a true lossless PNG re-encode can meaningfully shrink the file, but if you need PNG-level file sizes closer to JPEG territory, you'll eventually have to accept some lossy trade-off or switch format entirely — usually to WebP, which supports both modes and typically beats PNG by 25-35% at equivalent visual quality.

A practical workflow

For most people the fastest route is a browser-based compressor rather than installing desktop software, provided you're comfortable with where your files go. Sejda, Smallpdf, and iLovePDF all offer decent image compression alongside their PDF tools, and TinyPNG is a solid dedicated option for PNGs specifically. Konomic's image compression tool (part of its wider PDF toolkit at konomic.io) works the same way — you upload the file, it applies size-appropriate compression automatically, and you download the result. It runs on EU-based servers in Germany and deletes uploaded files within an hour, which matters if the images contain anything client-facing, unreleased, or personally identifiable — there's no account needed and nothing lingers afterwards.

Whichever tool you use, the process is the same: pick the right format for the content, resize to the dimensions you'll actually display, compress once at a sensible quality level, and inspect the output before publishing.

Getting the balance right

There's no single "correct" compression level — a hero image on a homepage deserves more care (and can afford a slightly larger file) than a thumbnail in a gallery grid. As a rule of thumb: if you can't tell the difference at normal viewing size after compressing, you haven't lost quality that matters, even if the file is technically no longer identical to the original. That's the practical definition worth working towards, rather than chasing pixel-perfect fidelity that nobody will ever notice.