Abstract: Normal mapping is a widely used technique in real-time graphics, but so far little research has focused on compressing normal maps. Therefore, we present several simple techniques that improve the quality of ATI's 3Dc normal map compression algorithm. We use varying point distributions, rotation, and differential encoding. On average, this improves the peak-signal-to-noise-ratio by 3 dB, which is clearly visible in rendered images. Our algorithm also allows us to better handle slowly varying normals, which often occurs in real-world normal maps. We also describe the decoding process in detail.