On Mon, Sep 13, 2010 at 05:35:55PM +0930, David Gowers wrote:
> I've just implemented
> A) a better test for roundtripping (slow, though.)
> 
> According to this test, we currently badly roundtrip in approximately
> half of the 256 possible cases. Most but not all of these errors are
> truncation errors.

I just checked it, I think it's 2% of the pixels, not 50%. Just remove
pixels with alpha <= 1 from the input and the error goes away completely.

We can't do anything about the roundtrip error at alpha <= 1 because after
premultiplying the original 8bit value is squeezed into a range that
contains fewer than 256 values.

-- 
Martin Renold

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