Dark Slide Ink-Saver Inverter

How it decides what to flip

Each page is rendered to a canvas and measured: if less than half the pixels are dark, the slide is already ink-friendly and is left alone. Dark pages get their grayscale inverted — white text on black becomes black text on white — while 32×32 px blocks whose channel spread exceeds the saturation threshold (photos, diagrams, colored charts) keep their original colors, so X-rays and figures don't turn into negatives.

Everything runs locally with pdf.js; your course material never leaves the browser. The toner-savings number compares dark-pixel coverage before and after the flip — a rough planning figure, not a lab measurement.