Guides

Answers to the questions that come up around the tools on this site. Each guide opens with the short answer and then explains it.

Why a PNG turns black when you convert it to JPG
JPG cannot store transparency, so every transparent pixel has to become a solid colour during conversion. Many converters drop the transparency and keep whatever colour sits underneath it, and in a browser canvas that colour is black. The fix is to fill the background with white, or any colour you choose, before the JPG is written. Our PNG to JPG converter does that for you.
Which favicon sizes you actually need
Most sites need four things: a favicon.ico holding 16, 32 and 48 pixel images, a 180 by 180 pixel apple-touch-icon.png for iPhone and iPad home screens, and 192 and 512 pixel PNGs listed in a web app manifest for Android. An SVG favicon is a worthwhile extra. Almost everything else in a typical favicon package is legacy.
How to check whether an online image tool uploads your photo
Open your browser’s developer tools, switch to the Network tab, and then process an image. If no request goes out carrying roughly the size of your file, the image stayed on your device. For a second check, load the page, disconnect from the internet and run the tool again: a tool that really works locally keeps working.