An annotation tool for people who look at night frames all day

Before the 5,000-frame pilot, we had to decide where people would actually do the work. We built our own, because our problem had some odd corners.

The biggest one: dashcam footage at night. Plenty of our frames are dark, noisy and low-contrast, and our annotators spend hours on them in a single shift. A bright white interface around a black frame makes your eyes re-adjust every time you glance at the class list. Do that a few thousand times and you have a headache by lunch. So the tool is dark, and the image is always the brightest thing on screen.

Colour caused the second problem. Our twelve classes each get a saturated colour, spread around the wheel so neighbours never look alike on a night frame. That means the interface itself can't use bright colour anywhere, or someone will read a button as a bounding box. The chrome stays warm and quiet. Green and red only ever mean pass and fail.

Third: nobody should ever lose work. Twenty minutes of careful boxes has to survive a dead battery, a dropped connection or a closed tab. We treated that as rule one, above speed.

Speed came next. The mouse draws and drags boxes, and that's all it does. Classes, variants, submit and navigation are single keys, and the keys sit on screen so nobody has to memorise them.

The last idea matters most to us. Every annotator sees their own numbers all the time: frames done, median seconds, pass rate, what they've earned. It isn't a game. It just makes the deal legible, and people who can see the deal tend to trust it.