DISAPPEARANCE OF WATER ON THE WEB SURFACE IN A FOURDRINIER PAPER MACHINE IS INDICATED BY THE DRY LINE, AND SCENE ANALYSIS IS USED FOR OBSERVATION OF ITS POSITION AND FORM. SAMPLING RATE OF 1 FRAME/SEC IS REACHED WITH A COMBINATION OF CCD CAMERA, PC, FRAME GRABBER AND ACCELERATION CARD. THE DRY LINER IS EXTRACTED FROM THE IMAGE BY STATISTICAL SEGMENTATION AND SECOND DERIVATIVE METHODS OF EDGE DETECTION. THE DIFFICULTIES INVOLVED IN THE OBSERVATION OF THE DRY LINE BY HUMAN EYE HAVE BEEN SOLVED BY A CAREFUL CONSIDERATION OF THE OPTICAL LAWS OF LIGHT REFLECTION AND REFRACTION.