Hi Scott,

From: "Scott Dattalo" <scott@DATTALO.COM>
>
> I think this may be what you're looking for:
>
> http://www.dattalo.com/technical/software/pic/medfilt.asm
>

Thanks for this it looks interesting. However I don't think the code you
gave a pointer to does what you just described (it seems to do a lot more!).
The code you have given a pointer to seems to maintain a secondary set of
pointers to 16 bit data (not 12 bit) that are used to maintain a sorted
version of the circular buffer. Then when you want to obtain the actual
output of the filter you can drop an arbitary number of entries from the low
and high end of the sorted data (as defined by high index and low index) the
remaining middle data points are then summed and used to provide an average
of these points. I may have got this wrong but I think this is what the code
does (and it seems to do it very well). This would appear to be a superset
of your described algorithm did you by any chance refine one into the other?

Anyway thanks a lot for the input.

Refering to your originnally described algorithm I have been thinking along
similar lines. In psudoe code I was thinking of doing the following

add_data_point(val)
    /* maintain simple circular buffer of ARRAY_SIZE data items */
    data[index] = val
    index = index + 1
    if (index >= ARRAY_SIZE) index = 0


get_filter_value()
    /* get hold of the average of the data points dropping the highest and
lowest sort of comined median and average filter */
    low = MAX_VALUE
    high = MIN_VALUE
    sum = 0;
    for(i=0; i<=ARRAY_SIZE;i++)
        sum = data[i] + sum
        if (data[i] > high) high = data[i];
        if (data[i] < low) low = data[i];
    sum = sum - high - low;
    return sum/(ARRAY_SIZE - 2)

I think that the above is equivalent to the mechanism you have described
except that it does more work when the data is needed rather than when it is
inserted. Is this correct? Or have I got things totally wrong?

Thanks again

Andy

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