Converts between image formats inside the Worker. PNG, BMP (32-bit with alpha), GIF (median-cut palette of up to 256 colours, LZW compressed, transparency kept) and ICO (PNG-compressed entries at the sizes you list) are written in pure JavaScript; SVG wraps the raster as an embedded PNG image; JPEG and WebP use the browser encoder with a quality setting, and transparency is flattened onto a background colour for JPEG. Non-PNG inputs are decoded by the browser. Everything runs locally.