You may decide if you what to display your image to actual pixel height or a percentage height of the frame.
- Height (%) will render your image to be a % of the frame. If you use a % width and a % height then the width will override height. Given the nature of vertical scrolling 'Height (%)' is infrequently used. Leave this field blank unless for a very specific purpose (e.g. thin portfolio images).
- Height (px) will set the image to a fixed pixel height.