Outline objects with polygons and export them

Which tool for which shape

The Polygonal Lasso places one straight segment per click, which suits boxes, signs, screens and buildings. The Pen draws Bézier paths, so a curved bottle or a car roof follows its edge with a few points instead of dozens. The Magnetic Lasso snaps to edges as you trace, a quick way to draw polygons on images where the object stands out from its background. Hold Space with any tool to pan while you trace.

Whichever tool you use, the result is a mask on its own layer, so you can fix a polygon afterwards with the Brush or Eraser without redrawing it.

How the outline is exported

At export each object’s mask is traced into a polygon and simplified to sub-pixel accuracy, so the points follow the edge closely without thousands of redundant vertices. An object made of two separate parts gives two polygons. In COCO JSON (Pro) both sit under the same annotation; in YOLO segmentation labels (Pro) each becomes its own line with the same class index. COCO stores every outline as a flat list of x and y pixel coordinates.

Polygons cannot describe a hole, such as the gap inside a handle or a ring. When an object has one, the COCO export switches that object to RLE, and you can choose RLE for every object if your pipeline prefers it.

SVG outlines for design work

Polygon segmentation labels are not only for training. The SVG outlines export (Pro) writes each object as a vector path, optionally with the photo embedded, ready for Figma or Illustrator. Shapes drawn with the Pen keep their exact curves in the SVG. That helps when the same outline is needed both as a training label and as artwork for a product page or a diagram.

Before you export

Zoom in on corners and thin parts, where a polygon annotation tool most often cuts in. Remove specks clears islands too small to matter, and Keep largest drops fragments from a rough lasso, and Colour layers by class shows at a glance whether every polygon carries the right category. Everything happens in your browser, so the images you outline stay on your computer.