at its original position of the picture 20 a if all the reference point images 21 23 are still at their original positions it is confirmed that the interactive control apparatus 11 is in the idle status when it is confirmed that the interactive control apparatus 11 is still in the idle status the control circuit 112 can further reduce the frame rate or sampling rate of the image sensor 113 or reduce the flashing frequency light projection frequency of the light source 13 to save more electric power what is described in the above i e if one reference point image or bright spot disappears in the next picture the interactive control apparatus 11 is switched to the operation status is only an example it can be arranged so that if any one bright spot still exists in the next picture the system is kept in the idle status or it can be set to keep the system in the idle status when at least n bright spots still exists in the next picture the picture 20 b of fig2 b is obtained by only scanning the pixel cells of the three reference point images however there might be some noise for example due to some slight vibration of the table supporting the interactive control apparatus 11 which causes an incorrect judgment to determine that the interactive control apparatus 11 has left the idle status to avoid such incorrect judgment the scanned.