Multi-dimensional array edge/border conditions
- by kirbuchi
Hi, I'm iterating over a 3 dimensional array (which is an image with 3 values for each pixel) to apply a 3x3 filter to each pixel as follows:
//For each value on the image
for (i=0;i<3*width*height;i++){
//For each filter value
for (j=0;j<9;j++){
if (notOutsideEdgesCondition){
*(**(outArray)+i)+= *(**(pixelArray)+i-1+(j%3)) * (*(filter+j));
}
}
}
I'm using pointer arithmetic because if I used array notation I'd have 4 loops and I'm trying to have the least possible number of loops. My problem is my notOutsideEdgesCondition is getting quite out of hands because I have to consider 8 border cases. I have the following handled conditions
Left Column: ((i%width)==0) &&
(j%3==0)
Right Column: ((i-1)%width ==0) && (i>1) &&
(j%3==2)
Upper Row: (i<width) &&
(j<2)
Lower Row:
(i>(width*height-width)) && (j>5)
and still have to consider the 4 corner cases which will have longer expressions. At this point I've stopped and asked myself if this is the best way to go because If I have a 5 line long conditional evaluation it'll not only be truly painful to debug but will slow the inner loop. That's why I come to you to ask if there's a known algorithm to handle this cases or if there's a better approach for my problem. Thanks a lot.
