The present invention relates to the parallel calculation of convoluted data. In particular, the invention relates to Gaussian pyramid construction and parallel processing of image data, such as parallel calculation of repeatedly convoluted data for use in a SIFT algorithm. This is achieved by providing a method for obtaining a plurality of difference images from an original image defined by a plurality of pixels, said method comprising: Providing a plurality of blurring convolution functions, each of said blurring functions providing increasing degree of blurring of an original image upon convolution of said original image; establishing a plurality of difference convolution functions, Dif, by calculating the difference between two of said blurring convolution functions, each of said two blurring convolution functions providing different degrees of blurring of an original image upon convolution of said original image; and calculating a plurality of difference images from said original image, by convolving each of said difference convolution functions, Dif, with said original image to obtain difference images.