imgtranslator.com translates the text in an image and redraws it in place: a menu, a product photo, a manga page. OCR and translation run on a server. Erasing the original text and typesetting the translation happen on a canvas in your browser.

That erasing step is the subject of this post. The obvious tool for it is an inpainting model, which I deliberately didn't use for the first two months. A generative fill can quietly change things that weren't text, like a price on a ticket or a face behind a speech bubble, and nothing in its output tells you it did. So I wrote the eraser by hand, as pixel rules.

What follows is how the second version of those rules worked, how I measured it when there's no ground truth for a real photo, and the point where more rules stopped helping, which I can show with numbers.

The input

For each line of text, OCR gives me a box. Sometimes it also gives per-character boxes, depending on the engine.…