Lossless compression stores image data more efficiently while allowing the original pixel values to be reconstructed. Lossy compression discards selected visual information to achieve smaller files. Neither approach is automatically better; each serves a different purpose.

What lossless means

With lossless encoding, decoding the file reproduces the encoded pixels exactly. PNG is the common browser example. It looks for repeated or predictable data patterns without deciding that subtle texture is unimportant.

Lossless does not mean the entire file remains identical. Re-encoding can remove metadata, change chunk order, or use a different compression strategy while preserving pixels. Resizing also changes pixels, even when the output format itself is lossless.

Use lossless output for sharp interface captures, diagrams, archival steps inside an editing workflow, and graphics where small color changes matter. The PNG compressor creates a clean PNG and can reduce dimensions, but it does not offer a fake quality control the browser encoder does not support.

What lossy means

Lossy encoders model which image information can be removed with limited visual impact. JPEG and typical WebP settings are common examples. At moderate quality, discarded details can be difficult to notice at normal viewing size. At aggressive settings, blocks, ringing, banding, smearing, or texture loss become visible.

Photographs often tolerate lossy compression because neighboring pixels vary gradually and the scene contains complex detail. Text, icons, and line art expose artifacts more readily.

Quality values are encoder controls, not percentages of detail

A quality value of 80 does not mean “keep 80 percent of the image.” It is an encoder-specific control. Two formats—or even two encoders for the same format—can produce different size and visual results at the same number.

Treat quality as a dial. Start moderately high, inspect the actual image, and move down only while the result remains appropriate. For a step-by-step workflow that applies this dial in practice, see How to Compress Images Without Losing Visible Quality.

Repeated compression compounds damage

Lossy formats do not remember which details the previous encoder already discarded. Recompressing a recompressed file can add new artifacts. Keep a high-quality source and derive each delivery image from it.

Converting a JPEG to PNG does not restore missing information. It simply stores the already-decoded JPEG pixels losslessly, often in a larger file. Converting that PNG back to JPEG introduces another lossy generation.

Resizing is not compression mode

Resizing changes the pixel grid. Even if the new file is PNG, interpolation combines or invents pixels. That is separate from whether the encoder is lossy or lossless.

This distinction is useful: reducing excessive dimensions can achieve large byte savings while allowing a relatively gentle lossy quality. For many web and email tasks, that looks better than keeping huge dimensions and forcing quality very low.

When to choose each

Choose lossless when pixel fidelity, transparency edges, or editing latitude is important. Choose lossy for photographic delivery when smaller transfer size matters and a visually equivalent result is sufficient.

Sometimes keep both: a lossless master and lossy delivery copies. Storage and delivery have different requirements.

Conclusion

Lossless compression preserves encoded pixels; lossy compression trades selected detail for smaller files. Make the choice based on content and destination, then verify the output. The image converter lets you compare JPEG, PNG, and capability-checked WebP results locally.