They are ever present. By comparison, DLPs have virtually no mask. In normal use DLPs project a virtually seamless image. Dual Scan Passive Matrix Newer version of the original passive matrix technology, where the screen is controlled by two processing systems. Contrast remains terrible.
Dual scan is used in the least expensive LCD panels.
If that range is limited, it will be difficult to distinguish between say, pure white, and the lightest grays. Simply put, subtle details disappear without adequate dynamic range. The electronic whiteboard adds a whole new dimension. Or edited later. In addition, many electronic whiteboards will work with projectors, allowing annotating of presentations, controlling the computer, entering data, and much more.