File formats
JPG, PNG or WebP: which image extension should you choose?
By ResizeFox · Published
Choose the file format from the job the image has to do. A photograph for a form, a transparent logo and a website illustration have different needs. The smallest result is only useful if the destination can open it and the visible detail remains suitable.
Quick reference
| Use | Size or purpose | Note |
|---|---|---|
| JPG / JPEG | Photographs and broad compatibility | No transparency |
| PNG | Transparent graphics and sharp artwork | Often heavier for photos |
| WebP | Web images when supported | Supports transparency |
Step by step
- Check which extensions the receiving website accepts. If it specifically asks for JPG, do not send WebP even if that file is smaller.
- Keep the original file. Open it in the ResizeFox tool on the home page and select Convert after choosing your image.
- Choose the output format. For a transparent logo, use PNG or WebP; choose JPG only when a solid background is appropriate.
- For JPG or WebP, adjust quality and convert. Inspect small text, smooth gradients and subject edges rather than judging only by the file-size number.
- Download and check the extension. Open the downloaded file once before uploading it to the destination.
JPG and JPEG are the same format
The .jpg and .jpeg extensions both refer to JPEG images. A form may still implement a narrow extension check, so follow its instructions. Renaming .png to .jpg changes the filename, not the underlying encoding; an actual conversion is needed.
JPEG is useful for many photographs, but it cannot represent transparent pixels. In ResizeFox, conversion to JPG paints those areas white. That is useful for a photo on a white canvas and unsuitable for a logo that must blend into a dark header.
Why a tiny PNG can become a bigger JPG
Flat graphics can encode efficiently in PNG. Converting them to a photographic format does not guarantee a smaller file. In our local browser check, an 800 × 600 transparent striped test image was 5.59 KB as PNG, while one JPG result targeting 20 KB was 19.86 KB. This is a single synthetic example; other images and browsers produce different results.
The dedicated size-limit tools now preserve a supported original file when it is already within the limit. For that same test image, the result remained PNG at 5.59 KB. If you deliberately need another format, use Convert instead of expecting the size tool to force a conversion.
Transparency and visible quality need separate checks
A white preview background can make a transparent and an opaque image look similar. Test a logo against the intended page background in your design workflow. For text artwork, examine thin strokes at normal display size and avoid exporting repeatedly from already compressed copies.
WebP can be useful when a web workflow supports it, but a document portal may reject it. File-size efficiency does not override format compatibility. Keep a source copy so you can create a different export without losing another generation of detail.
See the tradeoffs yourself in the Image Compression Lab: compare text, gradients and transparent graphics with downloadable results.
Sources and further reading
Platform specifications and application rules can change. Refer to the current destination instructions; the worked calculations and preparation choices in this tutorial are not a guarantee of acceptance.