1. A method of processing a short series of X-ray images to form a composite image comprising the steps of making a short series of X-ray images of an object, and determining a composite image to be displayed from said short series of X-ray images, said composite image being formed from at least one last X-ray image, said last X-ray image being multiplied by a weighting factor .alpha. smaller than or equal to 1, and said composite image being formed from a previously formed composite image, said previously formed composite image being weighted with a complementary weighting factor (1-.alpha.), wherein said weighting factor .alpha. is dependent on the number of X-ray images of said short series of X-ray images previously processed, said weighting factor .alpha. having an initial value of 1 and a value smaller than 1 for each new composite image formed, each of said weighting factors being smaller than or equal to a preceding weighting factor.