[Mp4-tech] DCT causing black dots

[mike toon]

Hi,
Currently working on a DCT/IDCT implementation in C and I'm encountering a problem with the reconstructed image.
At high bitshift levels black dots appear in the top-left corner of a DCT block, has anyone encountered this before or have any suggestions as to why this may be occurring.
I am scaling up by 10000 using integer arithmetic and taking account of rounding. The algorithm I use is described here: http://www.geocities.com/ssavekar/dct.htm
Thanks,
Mike.
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