Compressing an image to an exact file size, in the browser

"Make this photo under 100 KB" is one of the most common things people need

from an image tool, and one of the few things almost no image editor exposes

directly. Photoshop gives you a quality slider. cwebp gives you -q. The

canvas API gives you a float between 0 and 1. None of them takes bytes.

The reason is that the mapping you want does not exist in the encoder. You ask