High Definition Video Production
The purpose of this information is to clarify some of the terms relating to new video technology and
high definition (high def or HD). Today high def is a much over used and sometimes misleading term. Some
cameras today, including the inexpensive flip type cameras claimed they record in HD. Well they do, sort of.
Let me explain.
3 Main Components to Any Video
There are 3 main, crucial components to any video camera today: the lense; the image
sensors that pick up the light and convert it to a digital signal; and the recording
The lense determines the clarity
and sharpness of the image being recorded. Professional lenses can cost a lot. For one of our cameras we paid
$7,500 just for the lense alone. As with most things in life, you get what you pay for. There is no comparison
between a $50 lense built into a flip camera and the lense of a professional video camera.
The image sensors are the chips
that capture and convert light into electrons. Lower end video cameras (even those costing $2,000 to $3,000) use
just one sensor. Compared to cameras with only one sensor, three-sensor cameras provide superior image quality
and resolution. By taking separate readings of red, green, and blue values for each pixel, three-sensor cameras
achieve much better precision than single-sensor cameras.
The recording format the camera
uses has been changing the past few years. The latest format is completely digital doing away with video tape. Each
recording format has pluses and minuses. One of the main factors with a digital format is how much compression is
used, and that affects the overall quality.
The high definition camera we are using is the based on the MPEG-2 compression format. This format
is both highly reliable and versatile. Developed by the Moving Pictures Expert Group (MPEG), it is one of the
most widely used compression schemes in the industry for camera acquisition, over the air broadcast, cable
and satellite TV. The format supports the highest HD quality with Full HD 1920x1080 resolution,
up to 50Mbps bit rate and 4:2:2 color sampling.
4:2:2 color sampling provides twice the color resolution of ‘regular high def’ and other codecs that
use 4:2:0 color sampling. 4:2:2 provides ultra-fine transitions in tone and color and maintains the
highest quality image for use in post production.
Other less expensive cameras use very high compression, lower bit rates and 4:2:0 color sampling. As
a result the colors are not as true and the images not as sharp and these formats are generally difficult to
edit with. Overall the quality of the image is vastly different.
Video Switcher for Live
A video switcher takes the video signal output of: several cameras; playback devices such as a VCR or DVD player; and laptop
output (as in the case of a presentation using PowerPoint) and feeds into a box called a switcher. The
switcher blends the individual video cameras and the PowerPoint presentation on the fly with dissolves,
wipes, and other effects.
Video switchers are available from $500 up to $40,000. One of the main differences is how much noise
they generate and what is the quality of the input signal they will take. Today, the highest quality input is
HD-SDI (high definition, Serial Digital Interface) which is basically an uncompressed high def digital signal. This is what we used. The video
camera must have an HD-SDI output and the switcher an input for HD-SDI. Most switchers are not as high
quality and pass much lower quality signals resulting in a degraded picture. The other factor in a video
switcher is how many inputs they have. With one of the switchers I use, I can have as many as 8 HD-SDI video
sources, plus a variety of computer inputs.
With a video switcher, you do not want to be using high quality, High Def cameras and then lose all
that quality when it goes through the switcher.
What assures the highest quality HD video production is to have quality HD cameras with HD-SDI
outputs and a professional switcher which can input and output HD-SDI signals and has the
capability for a variety of computer inputs.