We thought pixel aspect problems would be all behind us when we went to the square pixel world of high definition. Not so. Many HD formats use pixel aspect compression to compress their media. For instance, 1920 × 1080 in DVCPRO HD is actually 1280 × 1080 in NTSC (1440 × 1080 in PAL). DVCPRO HD in the 720p format is 960 × 720. So in Photoshop (using square pixels), your circle looks like the one shown in FIGURE 4.10.
Figure 4.10 Even HD uses non-square pixels in some formats, as does this DVCPRO HD example here.
The good news is that with HD, there are only two image sizes: 1920 × 1080 or 1280 × 720. Regardless of your source footage, you can regain the correct pixel aspect ratio by scaling all HD still images to one of these two sizes.