A recent review in which the author effused over the new "professional" Panasonic AG-HSC1U AVCHD camcorder really pressed one of my buttons -- users who buy market-speak over technical reality and adopt consumer formats and products as "professional." It seems that marketing departments have become the new gods of all that is true and right.
What particularly got me about this review was its lack of consideration for the technical compromises required by smaller camcorders with smaller imaging chips and smaller bandwidth recording formats. These "compactions" -- imager size and recorded bandwidth -- reduce the delivered resolution.
More With Less
Video resolution is related to the luminance bandwidth in the recorded signal. Smaller imagers capture less light and therefore less resolution. Lossy compression formats like DV, HDV, and XDCAM HD are based on throwing out high-frequency information that will be least noticed by the human eye. In other words, resolution is sacrificed in the hopes that viewers will not notice. HDV and XDCAM HD are worse yet because they use long-GOP MPEG-2 to add temporal compression to produce P and B-frames.
Many DV camcorders use 1/3-inch imaging chips followed by 10:1 DCT compression with 4:1:1 sampling (for NTSC). The reason this high compression rate "works" is that the smaller chips don't capture more resolution than the DV format can deliver.
Comparing an uncompressed capture direct from the camera to a DV capture from the camera's IEEE-1394 port, there is little discernable difference. For a first-generation DV camcorder like the Panasonic AG-DVX100, this is about 400 TV lines per picture height (LPH).
However, when you move away from I-frame only formats like DV to long-GOP formats, the additional compression creates noticeable resolution degradation in side-by-side comparisons with the uncompressed video. The designers of long-GOP formats were focused solely on easing bandwidth requirements for final distribution. They explicitly acknowledged that these formats were not amenable to acquisition and post-production tasks.
In fact, it was FAST Electronics (since absorbed by Pinnacle which, in turn, was absorbed by Avid) that got higher bandwidth 4:2:2 sampling I-frame only profile incorporated into MPEG-2 specifically to address this issue. For SD work, 50 Mbps MPEG-2 4:2:2P@ML I-frame only produced results indistinguishable from the proprietary "online" 2:1 M-JPEG compression schemes that were the de facto NLE standard capture formats of the day.
HDV Strategy
With HDV, manufacturers did an end run around the "acquisition and post production" profile created specifically for professional use. Instead they employed a higher level (High 1440) of the MPEG-2 main profile to create a long-GOP, highly compressed "HD" format for consumer handheld camcorders, many with a single 1/4-inch imaging chip. With no affordable HD format for professionals on a budget (like so many state and local government agencies and independent contractors), many users latched onto these consumer camcorders, especially for HD "run-and-gun" applications.
But an HDV signal created from 1/4-inch to 1/3-inch imagers cannot deliver true HD resolution (specified to be over 800 LPH) in its allocated 19-25 Mbps bandwidth. It did produce noticeably better pictures than DV and used 16:9 as a native aspect ratio -- and so was hailed by manufacturers (and their "independent" early testers) as the format for HD field production. The marketing worked.
Manufacturers then took the same imagers, digital signal processing, and codecs, re-packaged them in larger camcorders with more "professional" switches and connectors, and, of course, sold them at higher price points than the "consumer" models. Users continued to reward them with more sales without taking a breath to look at the technology.
It was only after the fact that many discovered the downside to long-GOP, particularly for post production. Those problems have still not been completely overcome, they have merely been made more tolerable by throwing ever larger amounts of computing horsepower at them.
The new consumer HD format, AVCHD, provides little or no resolution improvement over HDV. Although the MPEG-4 codec is up to four times more efficient than MPEG-2, small imaging chips, 4:2:0 sampling, and long-GOP compression will provide no relief from HDV's post-production headaches. Small theoretical gains in picture resolution might be great for marketing purposes, but the human eye will likely be unable to detect them on common HD displays
Like MPEG-2, there is a higher bit rate I-frame only profile for AVC that is not only more amenable to post-production, but can deliver higher resolution given 1/2-inch to 2/3-inch imaging chips. Despite being simpler to encode than AVCHD (there is no need to do the temporal compression to produce P-frames, B-frames, and long-GOPs), the only manufacturer to implement AVC I-frame only, Panasonic, is maintaining the cost of camcorders for this format in a range above the 4K capable Red One system.
My wish for the New Year is that Panasonic (or another manufacturer) delivers a sub-$8,000 AVC I-frame only 4:2:2 sampling HD camcorder that truly delivers minimum HD resolution in a "ready to edit" format. Oh, and world peace, too.
Wayne M. Cole, CCV, CLVI, and member of the AGCV Board of Advisors, is also the owner of IHP, a video production company located Santa Barbara, CA. Contact him at wcole@ihpweb.com.
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