The HD Formats:
HD is a general term and it covers all the Hi Def formats including HDV really. But most people, at least most working professionals in film or broadcast, when they are referring to HD are talking about material acquired on HD Vision, HDCAM, DVCProHD, or HDCAM using a picture size of 1920x1080 or 1280x720 and color sampling of at least 4:2:2. *Note: HDCAM is 3:1:1, but that's the exception.

Comparing HDV Formats:
HDV refers to a tape format that was really designed to be the replacement for DV, but for once the industry replaced a format with another format that uses the same tapes. On a DV videocassette, you can get two types of HDV footage which is HDV 1 and HDV 2.

The JVC's HDV 1 uses a 1280x720 image size which reduces the data rate to 19mbps and reduces the GOP to 6 frames. Progressive scan on a JVC camera also makes a difference in an increase in perceived sharpness, but on the flip side progressive scan can increase motion artifacts from camera or subject motion, particularly horizontal.

While the Sony’s HDV2 uses a 1440x1080 frame size (as opposed to HD formats with 1920x1080), which has the same data rate as DV (25 mbps) but uses MPEG compression to create 15 frame (NTSC successor); or another popular HDV format uses 12 frame (PAL successor) groups of pictures. The basic compromise here is image quality as the image compression is very aggressive, a necessity to fit that much picture on a DV cassette.

Since HDV is Transport Stream MPEG (and not studio profile) its color sampling specification is 4:2:0, as a DVD or satellite signal would have. This is effectively equal to the color undersampling that DV does with the 4 pixel blocks shaped as 2x2 in 4:2:0, vs 4x1 pixel blocks in DV’s 4:1:1.

Both types of HDV have an 8 bit color depth, which indicates 256 possible values for each color channel.

Dissecting Some HD/HDV Formats Specs:
With the other HD formats mentioned, each frame is handled individually instead of compressed as a group. This increases quality, but there are some trade-offs in this group as well.

HDCAM actually undersamples color to 3:1:1 (remember plain old DV is 4:1:1...3:1:1 is a bit better) and even though it records 1920x1080 images, it's really only laying 1440x1080 to tape to make the data fit.

DVCProHD uses 4:2:2 color sampling which is certainly better than 3:1:1, but Panasonic also needs to record a reduced res image to cram all the data on tape. The 1280x720 that the Varicam DVCProHD camera does so well is actually only 960x720 on tape.

HDCAM and DVCProHD are both 8 bit color depth formats.

The HDCAM SR uses far less compression, but require dual-link SDI to pump the video signal to a deck or a server and the equipment is currently not terribly cost effective for many projects that don't require impeccable quality and which have been budgeted accordingly.

In general, because of the nature of HDV, all the cameras that are currently available do not have interchangeable lenses and are just generally less expensive than the more "production-oriented" HD tape formats. The configuration of the camera can have as much or more to do with image quality than the compression and, generally, HDV cameras are configured to be inexpensive to fit their intended market.

HD/HDV Post Production:
The issue gets more confusing when post production is introduced as you can take your HDV footage and edit it "native" as MPEG or you can convert it into more conventional HD file-types and edit it with other types of HD content -- or you can easily output it to other HD formats. Since HDV primarily uses FireWire as its main "pipeline" and other types of HD use HD-SDI, converting the footage can be an advantage in those situations. Some users would prefer to edit their HDV footage as HDV -- it's been an on-going discussion as to the advantages and disadvantages of each approach.

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