Saturday, December 15, 2007

HD Primer

The ins and outs of entry and mid-level HD camcorders

Never before has the video industry seen such an explosion of formats as we're experiencing today, and along with the plethora of formats comes confusion about what HD is and what it isn't. Rarely does a day go by that we don't hear the phrase "True HD" or "Full HD" in the context of comparing camcorders and/or formats.

If the camcorder displays 1280 x 720, or 1920 x 1080 on OUTPUT, it is indeed a "High Definition" camcorder. Truly!
Hopefully this simple statement clarifies HD. I believe the confusion stems from marketing campaigns in the early days of low-cost HD camcorders and discussions of imager sizes and recorded image sizes.

Although some manufacturers, evangelists, or editors might suggest that the sensor/imager of a camcorder determines whether a camera is an HD camcorder or not, the imager/sensor size isn't directly related to whether a picture is HD or not. DSP may be employed to create an HD output from the camcorder. In theory, a camcorder manufacturer might take a Standard Definition imager and use DSP (Digital Signal Processing) to upsample the SD image output from the imager, and store the image on tape, hard drive DVD, or memory card as an HD image. Of course, recording a VHS signal to HDCAM might make it HD, but the picture quality obviously comes into question.

HD camcorders range in price from $800.00 to $800,000.00; this article is predominantly focused on the lower and mid-level camcorders.

Various camcorders offer different sizes of imagers. The HDV format for example, is always a 1280 x 720 or 1920 x 1080 display, but various sized imagers may be employed to reach the display size. For example, the Canon XLH1 camcorder uses a 1920 x 1080 imager to generate a 1440 x 1080 recorded image. The JVC GY-HD200U High Definition 3-CCD MiniDV Professional Camcorder (Body Only)

uses a 1280 x 720 imager to create a 1280 x 720 recorded image. The Sony Z1 uses a 960 x 1080 imager to deliver a 1440 x 1080 recorded image. The Panasonic HVX200 offers the smallest imager of any HD camcorder at 960 x 540, slightly smaller (vertically) than a PAL SD imager, recorded to a 960 x 720 frame size (in 1280 x 720 modes). All of these camcorders upsample or downsample the recorded image, excepting JVC's HDV camcorders and Sony XDCAM EX. Their format is a full-raster format (meaning imager matches recorded frame size). SONY PDW-510 XDCAM CAMCORDER (DVCAM)
HD offers a 1440 x 1080 recorded image derived from a 1920 x 1080 imager, while SONY PDW-510 XDCAM CAMCORDER (DVCAM)
EX offers a 1920 x 1080 recorded and displayed image.

Imagers range in size from 1/4" to 2/3", depending on the camcorder model. The Sony HVR V1U features 1/4" imager set on the diagonal, providing a sample equal to 1440 x 1080, but using unique (and oft-debated) technology, the image is sampled at 1920 x 1080. SONY PDW-510 XDCAM CAMCORDER (DVCAM)
HD features a 1/2 imager, while Varicam and HDCAM products offer a 2/3 imager. The larger imagers are not only more light sensitive, but they also allow for shallow depth of field and a smoother image in most shooting situations.

Smaller imagers packed with many more pixels than their SD counterparts are prone to being low-light challenged. More pixels in the same space comes at the cost of sensitivity, although new imagers and DSP are making tremendous strides in low-light situations.

SxS card
HD images are stored on a variety of storage formats. The Sony HVR Z7U stores HDV tape simultaneously, while the SONY PDW-510 XDCAM CAMCORDER (DVCAM)
EX stores media on the new SxS (pronounced "S by S") cards that read incredibly fast. AVCHD is stored on memory sticks, DVD, HDD, and SDHD cards. XDCAM is stored on Sony Professional Discs, which uses Samsung BD-P1000 High Definition Blu-Ray DVD Player

technology to store HD media on optical storage. Panasonic uses the P2 card system, which is a PCMCIA card format. Grass Valley Infinitycam stores on Iomega REV discs, while RED and SI record to hard drive units. Higher end camcorders may record to tape, or use dual-channel SDI output to large hard drive arrays.

When dealing with the various flavors of MPEG (MPEG 2/AVCHD), the primary consideration is the bitrate at which the video file/frames are encoded. Ranging from 11Mbps to 50Mbps and differing ratios of compression, it can easily become confusing. Don't confuse compression with color sampling.

AVCHD varies the bitrate from 11Mbps to 16Mbps, depending on the manufacturer and model of the camera. HDV offers two bitrates that are constant bitrates (CBR). 720p offers a bitrate of 19Mbps, while 1080i/p is encoded at 25Mbps. SONY PDW-510 XDCAM CAMCORDER (DVCAM)
offers a variable bitrate (VBR) of 35Mbps and 50Mbps (depending on the model). SONY PDW-510 XDCAM CAMCORDER (DVCAM)
EX offers a VBR of 35 Mbps or a CBR of 25Mbps. MPEG is the same format as delivered over satellite and cable, DVD, Samsung BD-P1000 High Definition Blu-Ray DVD Player

, or Toshiba HD-A2 Single Disc High Definition DVD Player

. It's possible with some camcorders to shoot to disc or card and play back the footage immediately on a BD system.

HDV compresses media at a rate of approximately 20:1, while AVCHD compresses at nearly double the HDV ratio. HDV may be used for broadcast in many applications, whereas currently, AVCHD is predominantly a consumer format, and likely will be for some time to come. The benefit of higher compression is that it allows for storage of high resolution media on small or slow format devices such as memory stick, DVD, or hard drive. The drawback to higher compression is that color and detail may be compromised, particularly in scenes containing complex color and complex MAC MOTION P818 Series Softskin Recliner

. An AVCHD camcorder may manage broad latitude images (lots of dark black and bright whites) while holding static, and may manage low latitude images with some MAC MOTION P818 Series Softskin Recliner

, but combining wide latitude with high MAC MOTION P818 Series Softskin Recliner

is very challenging for highly compressed formats. HDV also suffers in some circumstances of high MAC MOTION P818 Series Softskin Recliner

and extreme chroma/color.

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