Does converting a blurry JPEG to PNG restore sharpness? Usually not: changing formats cannot recreate discarded detail. Website image optimization requires separating compression, pixel dimensions and format selection.
Judge the result for its intended use. No quality setting or reduction percentage is universally optimal.
1. Lossy versus lossless
MDN distinguishes lossless compression, which preserves the encoded information, from lossy compression, which discards some information. Ordinary web JPEG workflows are lossy; PNG compression is lossless.
A PNG is not necessarily an original image. Saving a previously resized or degraded JPEG as PNG preserves the current data, not the details that were already lost.
2. Resizing is a separate decision
A 6,000-pixel image displayed in a small area may carry unnecessary data. Excessive reduction can also remove detail needed for dense displays or zooming.
Identify actual display sizes, retain the source and export suitable variants. Change dimensions and compression separately to see which damages text or edges.
3. Match the format to the content
MDN's image-format guide documents format characteristics including transparency. Try lossy formats for photographs; inspect small text and diagrams carefully and consider lossless output.
Google's WebP documentation confirms support for lossy, lossless and transparency. A .webp suffix alone does not reveal the compression mode. Renaming an extension is not a format conversion.
| Content | Priority checks |
|---|---|
| Photograph | Detail, gradients and size |
| Screenshot with text | Readability, edges and straight lines |
| Transparent artwork | Alpha and edges on light and dark backgrounds |
| Diagram or logo | Sharpness; consider an available vector source |
4. A controlled export workflow
- Keep the source separate from experiments.
- Choose dimensions for the real placement.
- Export several format and quality candidates.
- Compare at the intended display scale and inspect sensitive areas.
- Record file size, dimensions and the final choice.
- Verify the uploaded public page, not just the local file.
Quality 80 in one tool need not match quality 80 in another. Compare actual output and size instead of treating that number as a universal visual score.
5. Avoid common quality traps
- Repeated lossy exports from already-compressed files.
- Using PNG for every photograph without comparing size.
- Reducing instructional screenshots until text is unreadable.
- Ignoring transparency on the final background.
- Judging only a small thumbnail.
- Assuming small files guarantee a fast whole page.
Image size is one performance factor alongside image count, loading behavior and layout. Aim for an appropriate file size that still communicates the intended information, not the smallest possible file at any cost.
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