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Start with where the image needs to work
A product photograph for an upload form, a logo for a colored page, and a screenshot of a spreadsheet have different requirements. A format that works well for one may make another difficult to use. Before converting anything, check the destination's accepted formats, dimension limits, and maximum file size. A smaller file has little value if the receiving application rejects it.
Then identify what the image must preserve. Is fine text essential? Must the background remain transparent? Is the picture mainly photographic detail, or clean shapes with a few colors? These questions narrow the choice more usefully than searching for a single best format. Keep the original and prepare a separate delivery copy for each destination.
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Match the format to the image's important details
JPG and JPEG refer to the same format. Its usual lossy encoding is well suited to photographs when some loss is acceptable, but it has no alpha channel for transparency. PNG uses lossless compression and can store transparency. WebP supports transparency and both lossy and lossless encoding; the format name alone does not tell you which encoding a particular tool uses.
Think of the table as a starting point for comparison. A screenshot can contain photographs, and a photograph can contain small labels. Inspect the detail your audience needs instead of classifying the whole file from its extension.
| Image or requirement | Starting choice | What to check |
|---|---|---|
| An opaque product or travel photo | JPG; compare WebP if accepted | Texture, gradients, and the resulting file size |
| Small text, a chart, or a screenshot | PNG | Readable lettering and fine lines at the intended size |
| A logo over different backgrounds | PNG; compare WebP if accepted | Transparency, soft edges, and compatibility |
| A form that explicitly requests JPEG | JPG | Background color, dimensions, and the upload limit |
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Decide whether transparency must survive
Transparent pixels let the page behind an image show through. Partly transparent pixels are also used around smooth edges and shadows. The PNG specification describes this opacity information as alpha. An opaque white rectangle is different from a transparent area, even if both look identical against a white page.
For an illustrative shop logo, imagine dark lettering with a soft shadow intended for both a white invoice and a blue website header. Keep a transparent source for the header. If an invoice system requires JPG, prepare a separate copy against the invoice's background color. That copy is suited to its particular destination; it should not replace the flexible original.
One logo, two delivery files
The transparent logo can remain PNG for a blue header. A JPG version on white may suit an invoice attachment, but placing that JPG on blue will reveal its white rectangle. Converting the white-background JPG back to PNG changes the encoding, not the background pixels already stored in it.
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A lossless format cannot recover earlier losses
Lossless storage preserves the pixel data being encoded; it cannot reconstruct information already removed before that step. Saving a heavily compressed photograph as PNG does not recover the original camera detail. Similarly, once transparent content has been merged with a solid background, an ordinary format conversion does not know which parts were originally transparent.
Keep a source you trust and make comparison copies from it. Avoid converting a file back and forth while searching for a smaller result. In particular, a quality number is an encoder setting, not a universal percentage of remaining image quality. The same number in JPG and WebP does not establish that their outputs look equally good.
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Judge a conversion by its result
WebP may be useful for a web delivery copy, but there is no fixed saving that applies to every file. Google's WebP FAQ explains cases where a converted file can become larger. An already compact source or a different encoding choice can change the outcome. Compare the generated bytes and visible detail together.
In Image Tools, JPG to WebP retains the source dimensions and lets you adjust quality. PNG to WebP can retain transparency, but its quality-controlled browser output is not promised to be lossless. PNG to JPG lets you choose a solid background. Those are different operations: select one according to the destination and the detail you need to keep.
- Inspect lettering, fine patterns, and smooth gradients at normal viewing size and up close.
- Check transparent edges against the background where the image will actually appear.
- Open or upload the downloaded file in the receiving application before replacing a working asset.
- Keep the source if future layouts, larger displays, or further editing are likely.
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Use resizing when the problem is too many pixels
A successful format conversion can still leave an image much larger in dimensions than its destination needs. Check its width and height in Image Info, then use the companion resizing guide to choose useful dimensions. File format, pixel count, and encoded file size are related decisions, but each answers a different question.
Image Tools works on one still JPG, PNG, or WebP at a time in your browser. Format conversion is not an archival copy: the resulting file need not retain the original metadata or color profile exactly. For work that depends on those properties, keep the source and verify the output with the application that will use it.
Sources and further reading
These references support the definitions and limits discussed in this guide. Worked scenarios labeled as examples are illustrative.
- MDN: Image file type and format guideThe capabilities and common uses of JPEG, PNG, and WebP, including transparency.
- W3C: PNG specificationPNG's lossless pixel storage and alpha representation.
- Google: WebP frequently asked questionsWhy converting to WebP does not guarantee a smaller file.
- Image Tools: PNG to WebPThe current converter's quality control, transparency support, and lossless limitation.
- Image Tools: PNG to JPGHow the current tool handles transparent pixels and the chosen background.