Computer Hardware

JVC and Sony introduced low cost HDV camcorders during 2004 that record 1080i or 720p on mini-DV tape. HDV uses inter frame compression across multiple frames rather than within a single frame to record 1080 by 50i, 1080 by 60i or 720 by 30p at or below the 25 Mbps data rate of the DV format. HDV stores less than one fifth of the information on DVCPROHD. To accomplish this feat, HDV relies on MPEG-2 compression.

The camcorder records in HDV or DVCAM at 60i or 50i and also at 30, 25 0r 24 frames per second although it’s not in true progressive mode. Two cinema Tone gamma correction curves intended to approximate film’s gamma response to light are selectable. The HRV-Z1U has a color correction feature that provides controls to adjust the color phase and saturation of up to two specific colors. Among the other interesting features are six user assignable function buttons and a viewfinder that is switchable between black and white and color.

Professional HDV camcorder designs using either prism based three CCD sensors or Bayer-filtered CMOS sensors are just arriving on the market so it’s too soon to know whether HDV will succeed as the low cost alternative for HD production. The Sony HVR-Z1U is the first professional three-CCD camcorder to be released. JVC’s professional HDV camcorder a prototype displayed at the 2004 NAB conference will likely use a CMOS sensor to capture HDV at 720p and it’s expected to be released soon. Sony’s HVR-Z1U uses a prism based imager with three 1 by 3 inch Super HAD CCDs in the 16:9 aspect ratio.

Operators have two choice of how to record the 24 frame progressive images. The industry standard pull down arrangement replicates the approach used to transfer film to NTSC video. Panasonic’s advanced pull down arrangement was developed to make extracting 24 frames from a 60i recording easier using desktop video editing software.

Panasonic’s AG-DVX100A uses a prism based imager with three progressive 1 by 3 inch 410000 pixel IT CCDs and has a fixed lens. This Prosumer camcorder captures at 60 fields per second or 30 0r 24 frames per second and records in the mini DV format at 25 Mbps.

MPEG-2 compression relies on both inter and intra frame compression to achieve greater efficiency than Motion JPEG (M-JPEG), which is the approach taken by most digital videotape formats because editing is simpler when compression is applied to individual frames ( intra frame) rather than across multiple frames (inter frame). MPEG-2 minimizes the bandwidth requirements by creating what are called long groups of pictures (GOP) and applying very high rates of compression. HDV uses a 15 picture GOP that begins with an intra frame (I-Frame). The I-Frame contains all the information to reconstruct a complete picture. It’s similar to a frame compressed using M-JPEG.