[opendtv] Re: Digital vs. Analog Quality

  • From: dan.grimes@xxxxxxxx
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 8 Jul 2008 08:56:39 -0700

I did a little more studying on the differences between the CECB converter 
box output and the NTSC reception.  For program material, I did find the 
resolution to be better on the converter box (baseband composite output). 
However, live material (i.e., news) still looked sharper and better on 
NTSC.  I am not sure why the live material on the ATSC looked softer.

But there were other differences that I noted that hampered the CECB:

Resolution:  The CECB had better resolution than the NTSC.  Details in the 
lit areas seemed to be the same on both, but much sharper edges on CECB 

Noise:  The CECB was much cleaner than the NTSC.  The noise level was much 
higher on the NTSC.  However, the noise masked the compression artifacts 
and dithered the inadequate quantization of the digital source.

Gamma:  The gamma seemed much lower coming out of the CECB.  The gamma on 
the NTSC was much higher and created a much more natural picture.

Black Level:  The CECB output a 0 IRE black level and there was a complete 
lack of detail in the blacks. Even if the black level (brightness) was 
raised on the monitor, detail could not be found in the blacks.  I could 
find no adjustments in the CECB to bring the detail back.  However, the 
NTSC did have black at 7.5 IRE and there was plenty of detail and 
gradiation in the blacks.  This suggests, to me, that the output of the 
server is correct but the CECB box is not converting properly.

Delay:  The CECB output was 3 to 8 seconds later than the NTSC.  I could 
watch an entire sequence of shots and switch to the ATSC and watch the 
same exact sequence.  I would hate to try and do a live call in show!

So now that I have studied the two pictures a little more, I can't say 
which is better, just that each have their strengths.  But overall, I am 
obviously seeing the limitations of the CECB and not those within ATSC.

Please feel free to provide feedback if I am analyzing something wrong or 
using the wrong terminology.


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