uchar* ptr = (uchar*)(img->imageData + y * img->widthStep);
for( int x=0; xwidth; x++ ) {

if(ptr[3*x]+20>=ptr[3*x+1]||ptr[3*x+2]+20>=ptr[3*x+1]){

ptr[3*x] = 0;
ptr[3*x+1] = 0;
ptr[3*x+2] = 0;

}

}