Additional information – Video acquisition formats
HDV HDV is directed towards the consumer and semi-professional market and is used by such manufacturers as Canon, Sony and JVC. It is the most common HD acquisitionformat and is tape based and uses the same cassettes as miniDV does.
HDV can be 1080i/p 720i/p that is usually recorded 1440x1080 and respectively 1280x720 is based on the Mpeg-2 compression, which is inter-frame, meaning that besides of compressing the image within individual frames it also compares and compresses frames with each other. The frames are analysed and compressed in specific “packages of frames”, or GOPs (Group of Frames), beginning with an I frame where a complete frame has been stored and following with B and P frames that record changes in comparison to the I frame. It has 4:2:0 colour subsampling.
Again as with any codec and format it still depends on the camera what kind of image quality it gives. The technical challenge of HD is that the increased resolution requires massively more data capacity to process and to be stored. Increasing resolution increases exponentially the need for bandwidth. That is why heavy compression is required. Most HDV formats, the format has slight differences depending on the manufacturer, use a bit rate of 19 Mbps or 25Mbps, compared to the 25Mbps of miniDV, which is SD. But the compression ratio of HDV is everything between 47:1 and 27:1, compare to DV which is 5:1. So there is little information left in the data, yet it can look astoundingly good. Where problems usually arise with heavy compressed formats is when you want to start manipulating the results. There isn’t enough information to be manipulated, but for documentaries and documentation this doesn’t need to be a problem if it the work is shot well from the beginning and doesn’t require a lot of correction afterwards. Especially exposure is critical with HDV. While the format seems to hold quite well if it needs to be colour corrected later, it quickly breaks down when you start adjusting the levels in post-production. But good exposure is anyway sign of a cameraman who knows what he or she is doing. So, if the project is shot well from the start, there is no real reason why HDV wouldn't be a good enough format for documenting art on video, or even become the next standard for it.
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