Changing the definition
Although the names DV and HDV could easily be confused, don’t go thinking the formats are similar. The first obvious difference is the horizontal resolution. That’s 720 pixels for Pal and NTSC, though Pal’s vertical resolution of 576 lines is considerably more than NTSC’s 480.With HDV there are two main fixed resolutions which are the same for Pal and NTSC. These are 1,280x720 and 1,440x1,080. But the frame-rates remain the same as for DV – 50 fields or 25 progressive frames for Pal, and 60 fields or 30 progressive frames for NTSC.
However, the HDV camcorders shipping so far are using interlacing for the higher of the two resolutions, and progressive scanning for the lower one. So Sony’s HDR-FX1E operates with 50 interlaced fields (called 50i) for Pal models or 60 for NTSC (60i), each at a resolution of 1,080 lines. JVC’s camcorders use the lower 720-line HDV, but progressively scan 30 frames a second.
This chart breaks down the HDV and DV formats, comparing the differentpopular resolutions and frame-rates. Note that anamorphic rectangular pixels are used
to maintain the 16:9 picture aspect ratio with 1,080i but that 720p uses square pixels
With all that extra resolution per frame – 1.55Megapixels for 1,080i and 922Kpixels for 720p (compared to 414Kpixels for Pal DV) – the frame-based compression used by DV has had to be been discarded.
Instead, HDV uses MPEG-2 transport stream, compressed to around the same data rate as DV of 25Mbits/sec (3.13MByte/sec). The main aim of doing that is to ensure that HDV fits nicely into the specs of existing tape carriages and interfaces used by DV and is able to use the same MiniDV cassettes.
That keeps down the camcorder development costs by using essentially the same mechadeck that MiniDV uses, and also not having to come up with yet another tape cassette design.
Following the same logic, HDV footage is captured to a PC using the well-proven FireWire connection. Capture software for HDV works rather differently for that used with DV, as we’ll be discussing a bit further on, but HDV camcorders can also shoot DV, making them very flexible – and DV footage is captured in the same way as from a DV-only camcorder.
In DV mode, the FX1E performed as expected, and was, we felt, on a par with other prosumer three-CCD models, such as Sony’s own VX2000. Although it would be silly to buy an HDV camcorder and then primarily use it to shoot DV, having DV capability certainly strengthens the buying arguments. An FX1E could readily be added to an existing portfolio of DV cams, doubling as an extra DV unit and adding HD capabilities to the portfolio as required.
The jury is still out on just how much better, in real terms, 1,080i is than 720p when it comes to the number of lines of resolution. On paper, 1,080i would seem the obvious winner, but things aren’t as simple as that - tests have shown that the FX1E only resolves 800 lines or fewer. This isn’t far above 720p but is still superior.
Know, too, that the FX1E has a quasi-progressive CineFrame 25 mode (CineFrame 30 on the NTSC model), which can be invoked using a Picture Profile. However, this isn’t a full de-interlace, and noticeably reduces resolution, almost to standard DV levels. So the FX1E is intended primarily for shooting 1,080i.
