Image segmentation represents the highest resolution understanding of visual scenes, where networks classify every pixel rather than simply drawing boxes around objects. This pixel-level precision enables applications that require detailed boundary information and exact shape understanding.

The leap from object detection to segmentation is analogous to moving from rough sketches to detailed coloring—instead of approximating objects with rectangles, segmentation creates precise masks that follow the exact contours of each object. This precision is crucial for applications like medical imaging, where the exact boundary of a tumor determines surgical planning, or autonomous driving, where understanding the precise shape of the road is essential for path planning.

Segmentation comes in several variants, each serving different needs. Semantic segmentation assigns each pixel to a class without distinguishing between instances of the same class—useful for understanding scenes but limited when objects overlap. Instance segmentation differentiates individual objects even within the same class, crucial for counting and tracking. Panoptic segmentation combines both approaches for complete scene understanding.

The architecture breakthrough that revolutionized segmentation came with Fully Convolutional Networks (FCNs) and later U-Net, which introduced skip connections between encoding and decoding paths to preserve spatial information. These innovations enabled networks to make dense predictions while maintaining high-resolution details.

Beyond traditional RGB images, segmentation techniques now handle 3D medical volumes, point cloud data from LiDAR, multispectral satellite imagery, and video sequences. The technology enables agricultural drones to precisely apply fertilizer only where needed, helps fashion applications allow virtual try-on of clothing, assists film studios with automatic rotoscoping, and enables augmented reality applications to seamlessly blend digital elements with the physical world.