Field guide · Browser image tools
JPEG vs PNG vs WebP: Which Format to Use
JPEG, PNG, and WebP solve different problems, so the best choice depends on image content, transparency, destination support, and whether the file is a master or delivery copy.
Open the private image tool →What to do
Use JPEG when a photographic image needs broad compatibility and transparency is unnecessary. Use PNG for lossless screenshots, diagrams, logos, sharp text, or transparent assets when its file size is acceptable. Use WebP for efficient website delivery of photographs and many transparent graphics in modern environments. Format conversion cannot restore detail that was already lost. Converting JPEG to PNG makes a lossless container around already-lossy pixels and often increases size. Converting PNG to JPEG removes transparency and may create ringing around text. WebP offers flexible compression, but a required upload workflow may reject it. Choose based on the destination first, then compare a real export instead of relying on the extension alone.
A reliable local workflow
Start with the original file whenever possible rather than an image that has already been repeatedly saved. Inspect its pixel dimensions and decide where the result will actually be used before changing a setting. A full-width website photograph, an email attachment, and a small profile picture need different dimensions. Resize first when the source contains far more pixels than the destination can display, then choose the output format, then adjust quality. This order avoids spending bytes on detail the final placement cannot show. Export one result and compare it with the original at the size people will really see. Look closely at faces, text, logos, gradients, shadows, and high-contrast edges because compression problems often appear there first. If the result is still larger than needed, reduce quality in small steps or lower the dimensions slightly. Keep the original file outside the tool so you can make a new version later. Local Image Lab creates a new download and does not overwrite your source.
How to judge the result
File size is only one measure of a useful result. Verify that the downloaded file opens in the browser or application where it will be used, that orientation is correct, and that any required transparency survived the conversion. JPEG does not support transparent pixels, so transparent areas are flattened by the browser during export. PNG is lossless but can be unnecessarily large for photographs. WebP often produces an efficient web result, although a legacy workflow may still request JPEG or PNG. Quality controls affect JPEG and WebP, not PNG in the same way. A setting of 80 is a practical starting point, not a universal target. Detailed textures may need more quality, while a simple background may tolerate less. A smaller output can also be visually worse than the byte reduction is worth. Compare before publishing and test on a typical phone as well as a large display. For important print, archival, medical, evidentiary, or production-master uses, retain the original and use a workflow designed for that purpose.
Privacy and browser limits
Processing happens in the current browser tab. The selected image is decoded into browser memory, drawn into an in-memory canvas, and exported as a new Blob for download. The application has no image upload endpoint, account, or cloud library in this release. That design reduces exposure to an application server, but it is not a promise that every part of the device is private. The operating system, browser, installed extensions, security software, managed-device tools, or a person with access to the device may still be able to observe files or activity. Very large pixel dimensions can exceed browser memory even when the compressed file is under 25 MB. If decoding or export fails, close other demanding tabs, try smaller dimensions, update the browser, or use a desktop editor. Browser encoders may produce different byte sizes across devices. The tool cannot guarantee an exact target size, preserve every metadata field, or reproduce every color-management feature of professional software. Always confirm the downloaded result yourself.