About subpictures


    A button subpicture is an image used for highlighting a button. The same image is used for all three states of a button (normal, selected, and activated). But by varying the colors and their opacity in each state, the highlighting can look quite different. This is achieved by defining the colors and opacity values for each state in a color index, or color set. When you build the DVD, the subpicture becomes a two-bit image used as an overlay. Each pixel references either one of three colors defined in the color set or is transparent. Each state has its own color definitions and opacity settings for all three colors.

    Therefore, while the same subpicture is used for each state, you can vary which elements (pixels) in the subpicture are visible by changing the opacity of the colors in each state. For example, using Photoshop, you can create a subpicture composed of three elements, such as a check mark, a button outline, and the button text. Each element references a different color. By adjusting the colors and opacity values, you can have the check mark appear next to a menu button only in the activated state. To do this you would make the check mark the sole item in the subpicture to use a particular color, say color 3. Then, you could define color 3 as transparent for all but the activated state.

    By varying the color and opacity values, this three-color button subpicture changes in each highlight state.
    By varying the color and opacity values, this three-color button subpicture changes in each highlight state.