Almost every image problem starts as a format problem. A photo saved as PNG is five times heavier than it needs to be; a logo saved as JPG loses its transparency; a screenshot saved as JPEG turns its text into mush. Getting the format right first makes most later decisions easy.

These articles cover what each major format is actually good at, how the modern ones (WebP, AVIF, JPEG XL) compare with the classics, and the underlying concepts — colour depth, colour spaces, aspect ratio, resolution — that explain why the differences exist. Start with the format comparison guides if you're choosing for a specific job, or with the colour and resolution pieces if you want to understand what's happening underneath.