Patent ID: 8774457

Claim:
A method for calculating a Time To Go, TTG, value between a vehicle and an intruding object, said method comprising: retrieving a first image of said intruding object at a first point of time, T 0 , and a second image of said intruding object at a second point of time, T 1 ; filtering said first image and said second image so that said first image and said second image become independent of absolute signal energy and so that edges become enhanced; setting an X fractional pixel position, X FRAC , to zero and an Y fractional pixel position, Y FRAC , to zero, where X FRAC denotes a horizontal displacement at sub pixel level and Y FRAC a vertical displacement at sub pixel level; selecting a scale factor, S i ; scaling said second image with said scale factor, S i , and resampling said scaled image to position X FRAC and Y FRAC ; resulting in a resampled scaled image, RS i I; calculating correlation values, C XPIX, YPIX, i , between said first image and said resampled scaled image, RS i I, for different horizontal displacements at pixel level, X PIX , and different vertical displacements at pixel level, Y PIX , for said resampled scaled image RS i I; finding a maximum correlation value at subpixel level, C i , based on said correlation values, C XPIX, YPIX i , and updating X FRAC and Y FRAC ; setting j=j+1 and scaling of the second image, calculation of correlation values, finding the maximum correlation value and setting of j to j=j+1 are repeated a first predetermined number of times; setting i=i+1 and selecting the scale factor, scaling of the second image, calculation of correlation values, finding the maximum correlation value, setting of j to j=j+1, and setting of i to i=i+1 are repeated a second predetermined number of times; finding a largest maximum correlation value, C MAX , among said maximum correlation values, C i , and the scale factor S i, MAX associated with the largest maximum correlation value C MAX ; and calculating the Time To Go, TTG, based on said scale factor S i, MAX .