Hello Tony,

>Change:     Filt <-- Filt + (New - Filt)*FFrac
>to:         Filt <-- Filt + ((New - Filt)+1)*FFrac
>Assuming you truncate the result.
>If FFRac is of another magnitude then change the '1' to
>reflect it, i.e. FFRac=4 means that you should add 2 instead.
>( i.e. an 'halfbit' of the output ).

    sorry but I don't get it. FFrac have to be between 0 and 1 right? (x/2)
is the same as (x*0.5). So I don't know what you mean with FFrac=4, maybe
(new-filt)/4?

    Your formula is great. It overcomes the problem of having to cast New
and Filt variables to 16 bit, but it suffers from the same problem as
Dave's.

    Filt <-- Filt + ((New - Filt)+1)/2
    Filt <-- 1 + ((0 - 1)+1)/2
    Filt <-- 1 + (0)/2
    Filt <-- 1

    My implementation solved this problem and don't have to deal with
negative numbers:

    if (filt < new) filt = filt + ((new - filt)+1) / 2;
               else filt = filt - ((filt - new)+1) / 2;

    The only problem I've found if when going from 0 to 255 or from 255 to
0:

    filt = filt + ((new - filt)+1) / 2
    filt = 0 + ((255 - 0)+1) / 2    <--- 255+1=256, it will roll to 0
    filt = 0 + (0) / 2
    filt = 0 <--- should be 255

    Anyway, I can solve this doing 16 bit operations or (easier) with a
couple of "if" clauses.

    Thank you very much,

    Brusque

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Edson Brusque                 C.I.Tronics Lighting Designers Ltda
Research and Development               Blumenau  -  SC  -  Brazil
Say NO to HTML mail                          www.citronics.com.br
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