[M4IF Technotes] Warping equations for 2 warping points

[Kris Huber]

I can't confirm this, but can deny it :-).  I think the only error (other
than some grammar errors) is that W'=2*alpha and H'=2*beta should be
W'=2^alpha and H'=2^beta (exponents) at the end of 7.8.4.  Without
understanding this error, the "fast version" of 2, 3, and 4 warping points
equations can't be interpreted correctly.
There is a sign-change on some of the coefficients when you compare the 2
warping points equations with the 3 warping points equations that generalize
them, but as long as encoder and decoder use same 2 warping points
equations, there should be no problem.  I found a perfect match between the
reference software implementations and independent implementation of the
equations based directly on the text for 1 through 3 warping points (the
microsoft reference software, I think it was, doesn't implement the
near-useless 0 warping points model correctly, if I recall).  I think
perhaps the equations for 2 warping points could have been formulated in an
alternative way, but that they are not in error.  If you still believe they
are in error, more detail would be helpful.
Regards,
Kris Huber
-----Original Message-----
From: "Sorin C. Cismas" <sorin   mobilygen.com>
To: <technotes   lists.m4if.org>
Date: Sun, 12 May 2024 00:01:09 -0700
Subject: [M4IF Technotes] Warping equations for 2 warping points
I think the warping equations for 2 warping points in Section 7.8.5
of N4350 are incorrect.  Can anybody confirm this?
Thanks,
Sorin Cismas