PNG

PNG (Portable Network Graphics) is the lossless raster format for graphics with sharp edges and flat colour, screenshots, logos, icons, diagrams and anything containing text. Lossless means it stores the image exactly: re-save it as often as you like and not a single pixel changes, the opposite of JPEG's generational decay.

PNG's standout feature is an alpha channel, true variable transparency, so an image can have soft, anti-aliased edges that blend cleanly onto any background. It compresses crisp, large areas of solid colour very efficiently, which is why a UI screenshot is far smaller and cleaner as a PNG than as a JPEG. The flip side is photographs: with their continuous tonal gradients, photos produce much larger PNG files than JPEGs, so PNG is the wrong tool for that job.

The simple rule is sharp edges and transparency to PNG, photographs to JPEG. When you assemble PNGs into a PDF or extract graphics from one, the format's transparency and exactness are preserved, and running the conversion locally keeps your assets on your machine.