What technique is used to control the visibility of lower layers in graphical images?

The technique used to control the visibility of lower layers in graphical images is opacity. Opacity determines how transparent or solid an element is in an image or graphic design. When an element has lower opacity, it allows the underlying layers to show through, creating a blending effect between the layers. This is particularly useful in graphic design and multimedia applications where layering elements can enhance visual depth and complexity.

For instance, if one layer has high opacity, it will obscure anything beneath it completely, while a layer with reduced opacity will let some of the underlying content be seen, creating a more visually dynamic composition. Adjusting opacity is commonly used in photo editing software and digital design tools to achieve desired effects like highlighting certain parts of an image while subtly displaying others beneath it.

In contrast, contrast pertains to the difference in luminance or color that makes an object distinguishable, brightness affects the overall lightness of an image, and saturation refers to the intensity of color. Each of these elements impacts the visual quality of the image, but they do not directly control the transparency or visibility of layers in the way that opacity does.