[AV Media Matters] Quality of several formats

[Jim Wheeler <Jimwheeler@aol.com>]

                     Comparison of Quality of Several Videotape Formats

The May 1999 issue of "Digital Video" magazine had a report of tests of
several videotape formats.  If you have Acrobat, you can download the report
from the Digital Video magazine website:
www.dv.com/magazine/1999/0599/formats0599.pdf

The Tektronix PQA-200 was used in all of these tests.  Figures 1, 2, 3 show
the high number of "bad" pixels caused by the H--8 format as compared to the
non-compressed 4:2:2 DDR format.

3/4" U-Matic and Hi8 did not do very well in these tests as shown in several
charts that summarize the test results.  Digital Betacam came out the best.
If D1, D2, D3, D5, and D6 had been included, they would have been in the
"best" category because they are uncompressed digital formats.  That was
known by the people at Digital Video magazine so why waste time and money
testing these formats.

Betacam-SP, DVCAM-25, DVCPRO-25, and Digital-S varied in quality depending
on
the type of information being reproduced.

S-VHS was not tested because they believed that it would be similar to Hi8.
DVCPRO-50 was not tested because it was assumed that it would be similar to
Digital-S.

The Tektronix PQA-200 makes picture quality measurements using the
Just Noticeable Difference (JND) method developed at the Sarnoff lab
to emulate the perceptions of the human visual system.  Several
different test patterns with motion are used and the Tektronix test
unit produces a number that represents the number of "bad" pixels. A
Picture Quality Rating (PQR) of zero means that there is no
difference between the test video frame and the same frame recorded
on a uncompressed 4:2:2 disc or tape machine.

1.0 = Degradation with a small perceptual impact
3.0 = Mild (but observable) image degradation
10 and higher = Clearly observable image degradation

Digital Betacam was .92-1.14 on two of the test images.  That's the
BEST of the compressed formats and also a very expensive
machine--about $40,000 US.

These tests confirmed what I already knew and that is that
compression will degrade the video quality.  I am surprised that the
mild 1.6 to 1 compression ratio of Digital Betacam produced a PQR
over 1.0.

There is another type of compression (wavelet) that is "loseless" up
to about 15 to 1 compression ratio.  Wavelet compression is used in
the TI E-cinema system.

Jim Wheeler