[Tig] Masters HDCAM SR

[glenn chan]

Regarding whether the 4:4:4 mode or 4:2:2 mode of HDCAM SR is better,
we could look at what JPEG does.  At high bitrates, JPEG codecs will
use a 4:4:4 because it yields better quality.  (*Not all JPEG codecs
support the 4:4:4 mode.)

Or think about it this way:  is it better to resize an image smaller
to save bandwidth, or apply DCT compression on it?  The latter is
better except at extremely low bitrates, where DCT compression falls
apart.  JPEG at extremely low bitrates looks terrible; you'll get
slightly better quality by scaling the image down, doing JPEG
compression on that, and then scaling it back up.  This is what JPEG
does to the chroma when it changes to its 4:2:0 mode at low-medium
bitrates.

I'd expect the same principles to apply to HDCAM SR.  And judging from
the DPXs here on the David Taylor's blog:
http://cineform.blogspot.com/2007/03/green-screen-challenge.html
It seems to me that the quality of 4:4:4 HDCAM SR is very good, and
that it would suffer if you had to use the 4:2:2 mode.  4:2:2 chroma
subsampling is not visually lossless in rare situations (red text on a
black background, fully saturated colors, red lights like LEDs on a
black background).  4:2:2 can get worse in quality since it suffers
generation loss if you have to repeatedly convert the signal from
4:2:2 <--> 4:4:4.

Glenn Chan
colormancer.com / color enhancement software
Toronto, Canada