Understanding image file formats
Choosing the right image format is one of the most consequential decisions you make when publishing photos online, sending files by email, or archiving a collection. The format determines how large the file is, how sharp it looks, whether it supports transparency or animation, and how widely it can be opened. This guide walks through the formats you will encounter most often and explains, in practical terms, when each one is the right tool.
JPG / JPEG
JPG is the workhorse of photography on the web. It uses lossy compression, meaning it discards visual information that the human eye is unlikely to notice in order to produce dramatically smaller files. For photographs — images with smooth gradients of colour and no hard edges — this trade-off is almost invisible at high quality settings and saves enormous amounts of space. The weakness of JPG shows up with sharp lines, text, and flat areas of colour, where compression artefacts (faint halos and blocky patches) become visible. JPG also does not support transparency. As a rule of thumb, save photographs as JPG at quality 80–92 and you will rarely see a problem.
PNG
PNG uses lossless compression: it reproduces every pixel exactly, with no quality degradation no matter how many times you save it. This makes it the right choice for screenshots, logos, diagrams, illustrations with text, and any image where crisp edges matter. PNG also supports an alpha channel, which lets parts of the image be fully or partially transparent — indispensable for logos that need to sit on top of coloured backgrounds. The cost is file size: a photograph saved as PNG can be five to ten times larger than the same image as a high-quality JPG.
WEBP
WEBP is a modern format developed to give the web the best of both worlds. It offers both lossy and lossless modes, supports transparency, and typically produces files 25–35% smaller than the equivalent JPG or PNG at comparable quality. For website performance this is a meaningful win: smaller images mean faster page loads and lower bandwidth costs. Browser support is now effectively universal across modern browsers. The main reason not to use WEBP is compatibility with very old software or certain print workflows that still expect JPG or TIFF.
GIF
GIF is an old format limited to a 256-colour palette, which makes it unsuitable for photographs. Its one enduring use is simple animation, though even there modern formats produce smaller, higher-quality results. If you do not specifically need an animated image that works everywhere, there is usually a better choice.
How to choose
Use JPG for photographs you want to keep small. Use PNG when you need transparency or perfectly crisp text and lines. Use WEBP when you control the publishing environment and want the smallest possible files for the web. When in doubt, convert a sample and compare the file size and appearance side by side — which is exactly what the tools on this site let you do, instantly and without uploading anything.