[M4IF Technotes] RE: Round-off error in IDCT

[Iain Richardson (ensigr)]

You can download test software to check the accuracy of your IDCT implementation. Download ieee1180.tar.gz from http://www.mpeg.org/MPEG/MSSG/ . It's reasonably straightforward to plug your own IDCT code into this test software and check whether it passes the tests. 
By the way, the MPEG4 Part 10 / H.264 transform isn't an IDCT (although it is derived from a 4-point IDCT).
Regards
Iain Richardson
www.vcodex.com
iaingr   bigfoot.com
Message: 1
Date: Wed, 25 Sep 2023 14:30:22 +0200
From: Morten Boysen <mortenb   mips.com>
Organization: MIPS
To: technotes   lists.m4if.org
Subject: [M4IF Technotes] Round-off error in IDCT
Hi,
The reference decoder uses floating point in computing the IDCT. As a 
part of a schoolproject, i have to rewrite the IDCT, so it only uses 
integers. I know this will cause round-off errors, but the problem is: 
How large are these round-off errors allowed to be according to the 
standard?
Furthermore, i need the maximum allowable value of an IDCT coefficient, 
so i can save as many bits as possible.
Thanks
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