the custom size field allows you to set customized width and height values different from the standard preset values of full, 1/2, 3/8, and 1/4.

    if the fixed ratio box is checked, when you enter a new size in either the height or width box, both dimensions are adjusted proportionately. if this box is unchecked, the height and width may be entered independently. if the dimensions are different from normal screen proportions, the image is stretched horizontally or vertically.

    the osprey video hardware is not capable of drawing all possible widths. depending on the color mode selected, it may require a width that is an even number of pixels or, for yvu9 and yvu12, a width that is a multiple of 16. the dialog lets you enter numbers that the hardware cannot utilize, but adjusts them as soon as you click on another field or button of the dialog.

    see proportion (pixel/aspect ratio) for more detailed information.