sliders for ajusting contrast and colour-intensity of output-file,
keep ratio aspect of input-image between the border of output image.
centre the input-image in the space between the borders.
enlarge untill it fills the space between the borders.
cut of or hide behind borders those parts of the image that are larger then the available space (this shoud allways be min. 0 or max. two sides, never all four sides).