One embodiment of the present invention sets forth a technique for compressing image data with high contrast between pixels within a tile and between samples within pixels without any data loss. Partial coverage layers are generated and written to a tile that includes multiple pixels without reading the existing image data that is stored for the tile. A partial coverage layer encodes image data, such as colors, and sub-pixel coverage information for each covered pixel in a tile. The use of partial coverage layers reduces the bandwidth used to store image data when a tile is not fully covered.