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[C. Park Seward]

Hi Tim,

Yes, Type "C" is Direct Color. The "4:1:1" is simply describing the ratio of luminance bandwidth vs. chrominance bandwidth. If the "4" is 6, then the "1" is 1.5.  It might be more accurate to state it as 4:1:.5.

It is used to describe the "container" to hold the digitized information. 4:2:2 is a very large container to hold .5 Mz  of chroma information since the sampled chroma bandwidth is 3 MHz.

Faroudja was the first person I know who made a wideband color encoder. My Accom decoder even has a "Equiband" mode (and chroma aperture correction) to decode the wider color bandwidth. However, I don't get to use it very often on Quad playbacks! 

Speaking of color, notice that the 1953 standard is far different from the 1999 standard.

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http://broadcastengineering.com/images/archive/308be09_fig2(1).jpg

"Signals using the legacy NTSC 1953 standard differ considerably from the newer standards, which have smaller differences. The implementation of the DTV standard will require a fair number of format conversions. In order to avoid color changes in the process, the input and output signal format colorimetry parameters will have to be considered and recalculated as required."

"Colour vision acuity, it was discovered, is different from that of brightness-only vision. In fact, if sufficient detail is available in the brightness of a scene, the detail in the colours can be reduced considerably with no apparent reduction in the sharpness of the scene. This allows the bandwidth of the colour difference signals to be reduced to half, or less, of that required for the luminance channel. This fact is further exploited in the NTSC system, where the colours to which the eye is least sensitive in terms of detail are assigned a narrower bandwidth, by transmitting I (orange-cyan) and Q (green-magenta) signals instead of (R-Y) and (B-Y) and allowing the Q signal only half the bandwidth of the I signal.

With a 3.57954545MHz subcarrier and a 4.2MHz video bandwidth in System M, only 600kHz is available for the usb of the colour signal. Some fiddling is done to ensure that one colour signal corresponds to the colours to which the human eye has least accuity - it sees them blurred in other words. This (called the Q signal) is given a 500kHz bandwidth while the other (I) is afforded the 'full' 1.3MHz. However, the reduction of the usb of the I signal to 500kHz in transmission means that either the receiver must filter the whole chrominance signal to 500kHz or perfom ssb demodulation on the 1.3MHz lower sideband of the I signal in order to avoid severe distortion caused by demodulating the vsb colour signal as a dsb one."

http://www.pembers.freeserve.co.uk/World-TV-Standards/index.html#Colour
http://www.pembers.freeserve.co.uk/World-TV-Standards/Colour-Standards.html#NTSC

Here is the PBS Tech Standard:

http://www.pbs.org/producers/redbook/2005-PBS-TOS.pdf

Since we live in a component digital world, we won't have to encode to composite video very often.

Seems that 170M actually reduced chroma bandwidth in NTSC:

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Best,
Park

C. Park Seward
2" Quad and 1" "C" transfers
Visit us: http://www.videopark.com




On Jun 16, 2010, at 11:41 PM, Tim Stoffel wrote:

> On Wed, 2010-06-16 at 15:13 -0700, C. Park Seward wrote:
>> Type "C" is composite and only has the resolution of 4:1:1. The chroma channels are 1.5 and .5 MHz (on a good day).
>> 
> Type C itself is not 4:1:1. It is direct color, so the composite
> waveform is faithfully recorded unlatered. It is the upstream NTSC
> encoder that sets the effective chroma 'sampling'.
> 
> SMPTE 170M called for equal bandwidth I and Q channels.
> 
> Tim Stoffel
> 
> 
> 
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