HD or Not
Techno-File
HDV vs. HD Formats
Comparing HD and HDV video results is no job for the techno-phobic. But before you shell out thousands for a new camera, here’s the technical lowdown comparing the two formats.
Compression: Borrow and Steal
If you have a television that receives digital cable in HD, you are watching what is in essence the HDV format. Video saved in HDV uses a compression method originally developed for broadcasting television. This method creates images 1440 pixels wide. HDV video is captured and edited on your computer in an MPEG-2 format. (The same format you typically use when burning a DVD.) Audio is compressed into an MPEG-1 format. In order to save space, HDV cameras look at multiple frames in your video and compress them into what’s called a group of pictures (GOP).
The first frame, as recorded, contains a complete picture (I-frame). The subsequent frames of video, as recorded, only contain information about the changes from the preceding frame. That’s why an HDV signal fits on a Mini-DV tape. But only the first frame has complete picture information. A typical HDV camera can record a 720p signal at 24, 25, 30, 50, or 60 frames per second; or a 1080i signal at 50 or 60 frames per second.
Compression: Frame by Frame
Cameras shooting in HD formats compress each individual frame separately. That’s one reason you may see differences between video from HD and HDV cameras, despite the fact that both say they are capturing 720p or 1080i.
Resolution: Fudge Factor
The pixel resolution of both HD and HDV video may not match the specifications. HD video recorded at 720p in DVCPro HD, for example, is 960 pixels across by 720 lines. In the same format, the HDV version actually has more horizontal resolution. It records 1280 pixels by 720 lines. The other major HDV format—1080i—as recorded both in HDV and HDCAM is 1440 pixels wide (it’s actually wider, but truncated to fit most TVs.).
Color: Critical Differences?
The HDV format uses a 4:2:0 sampling to acquire color information. Those three numbers refer to the “colorspace” in which images are sampled. That format is effectively identical to the 4:1:1 scheme used for a prosumer Mini-DV format. As you might guess, HD cameras retain a lot more color and luminosity information than HDV. HDCAM, for example uses a 3:1:1 sampling; and DVCPROHD is 4:2:2. Thanks MM Issue61
HDV vs. HD Formats
Comparing HD and HDV video results is no job for the techno-phobic. But before you shell out thousands for a new camera, here’s the technical lowdown comparing the two formats.
Compression: Borrow and Steal
If you have a television that receives digital cable in HD, you are watching what is in essence the HDV format. Video saved in HDV uses a compression method originally developed for broadcasting television. This method creates images 1440 pixels wide. HDV video is captured and edited on your computer in an MPEG-2 format. (The same format you typically use when burning a DVD.) Audio is compressed into an MPEG-1 format. In order to save space, HDV cameras look at multiple frames in your video and compress them into what’s called a group of pictures (GOP).
The first frame, as recorded, contains a complete picture (I-frame). The subsequent frames of video, as recorded, only contain information about the changes from the preceding frame. That’s why an HDV signal fits on a Mini-DV tape. But only the first frame has complete picture information. A typical HDV camera can record a 720p signal at 24, 25, 30, 50, or 60 frames per second; or a 1080i signal at 50 or 60 frames per second.
Compression: Frame by Frame
Cameras shooting in HD formats compress each individual frame separately. That’s one reason you may see differences between video from HD and HDV cameras, despite the fact that both say they are capturing 720p or 1080i.
Resolution: Fudge Factor
The pixel resolution of both HD and HDV video may not match the specifications. HD video recorded at 720p in DVCPro HD, for example, is 960 pixels across by 720 lines. In the same format, the HDV version actually has more horizontal resolution. It records 1280 pixels by 720 lines. The other major HDV format—1080i—as recorded both in HDV and HDCAM is 1440 pixels wide (it’s actually wider, but truncated to fit most TVs.).
Color: Critical Differences?
The HDV format uses a 4:2:0 sampling to acquire color information. Those three numbers refer to the “colorspace” in which images are sampled. That format is effectively identical to the 4:1:1 scheme used for a prosumer Mini-DV format. As you might guess, HD cameras retain a lot more color and luminosity information than HDV. HDCAM, for example uses a 3:1:1 sampling; and DVCPROHD is 4:2:2. Thanks MM Issue61
posted by arkietechs at 12:31 PM
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