Telegram offers three ways to send an image. Photo compresses to 1280 px at around 80% quality. HD (the SD/HD toggle in the editor, added in 2025) raises that to 2560 px. Send as file keeps every byte, up to 2 GB (4 GB with Premium), but the receiver gets a download rather than a preview.
Preparing the file at 1280 or 2560 px with sharpening means Telegram's own resize is skipped, and the quality loss drops to a single light encode.