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jecottrell
Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ
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| Median Filter Code Problem |
 Posted: Mon Mar 14, 2005 4:55 pm |
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I'm trying to implement the median filter recommended by SherpaDoug and I'm running into an odd problem. I was hoping a second opinion might catch something I'm not.
Here is the code I'm using to toss out wild balls coming back from the PNI ASIC:
| Code: |
signed int16 median_filter(signed int16 value_in) {
static signed int16 holding_array[3];
int i = 0;
static int counter;
signed int16 low_val = 32767;
signed int16 high_val = -32768;
int high_loc = 0; //location in array of high value
int low_loc = 0; //location in array of low value
signed int16 median_val;
holding_array[counter] = value_in; //put incoming val in array
if(counter < 2) { //increment array
counter++;
} else {
counter = 0;
}
for(i = 0; i < 3; i++) { //find and mark highs and lows
if(holding_array[i] > high_val) {
high_val = holding_array[i];
high_loc = i;
}
if(holding_array[i] < low_val) {
low_val = holding_array[i];
low_loc = i;
}
}
median_val = holding_array[3 - (high_loc + low_loc)];
printf("1 %ld 2 %ld 3 %ld\n\r", holding_array[0], holding_array[1], holding_array[2]);
printf(Median %ld\n\r", median_val);
return(median_val);
} |
Here is the output from a problem. It appears when the ASIC returns three consecutive readings that are identical.
Output:
| Code: |
1 -44 2 -44 3 -39
Median -44
1 -44 2 -44 3 -44
Median 32000 <------------------
1 -48 2 -44 3 -44
Median -44
1 -48 2 -42 3 -44
Median -44
1 -48 2 -42 3 -38
Median -42
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I'll try to figure it out in the mean time. Thanks again for all the great help,
John |
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jecottrell
Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ
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| Solved..... |
| Posted: Mon Mar 14, 2005 5:17 pm |
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Not 10 seconds after hitting the submit button I realized the sorting routine won't assign different locations to the same values. That then goons up the median picking routine......
Sorting:
| Code: |
for(i = 0; i < 3; i++) { //find and mark highs and lows
if(holding_array[i] > high_val) {
high_val = holding_array[i];
high_loc = i;
}
if(holding_array[i] < low_val) {
low_val = holding_array[i];
low_loc = i;
}
}
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Picking: (relies on a different value, 0-2, being assigned to high_loc and low_loc)
| Code: |
median_val = holding_array[3 - (high_loc + low_loc)];
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All I needed to do was to change:
| Code: |
if(holding_array[i] > high_val)
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to:
| Code: |
if(holding_array[i] >= high_val)
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so the marker would sequence with each subsequent equal value.....
I proved to my self that the median filter worked (sometimes I'm amazed by the simplest successes.)
| Code: |
1 -45 2 -42 3 -41
Median -42
1 -44 2 -42 3 -41
Median -42
1 -44 2 -44 3 -41
Median -44
1 -44 2 -44 3 6275
Median -44
1 -52 2 -44 3 6275
Median -44
1 -52 2 -39 3 6275
Median -39
1 -52 2 -39 3 -41
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