for( int j = min_col; j < max_col; j++, row += 3 ) {
if( row[0] < minima_r ) minima_r = row[0];
if( row[0] > maxima_r ) maxima_r = row[0];
for( int j = min_col; j < max_col; j++, row += 3 ) {
if( row[0] < minima_r ) minima_r = row[0];
if( row[0] > maxima_r ) maxima_r = row[0];