[M4IF Technotes] contradictory conformance requirements?

[Deepali Arya]

Hi all,
The visual conformance FDIS document has couple of contradicting statements.
Can someone clear these up for me please?
Section 4.4 : Definition of visual decoder compliance
The decoder shall reconstruct I-, P- and B-VOPs and sprites within +/-1
pixel difference compared with that generated by the reference software.
4.5.1 Static tests
- The static tests that involve the use of IDCT, IDWT or sprite warping, in
which case the test will check that the peak absolute error between the
values of the samples reconstructed by the decoder under test and the values
of the samples reconstructed by the reference decoder shall not be larger
than 2 when the reference frames used by both decoders are numerically
identical.
The first statement indicates that a decoder implementation can be off from
the reference decoder by maximum difference of 1. The second statement
indicates that a difference of 2 is acceptable, if reference VOPs are
numerically equal. Which is the right requirement? If the IDCT is 1180
compliant and follows Annex A of the standard, how much difference between
the final reconstructed pixels of the decoder is allowed?
Thanks.
Deepali Arya
Improv Systems Inc, Beverly.
Email: deepalia   improvsys.com
Tel:  (978) 927-0555 x18