Which parameter is primarily used to control the display brightness of an image?

• A. Window level
• B. Window width
• C. Pixel spacing
• D. Matrix size

Answer: (A)

The display brightness of an image is governed mainly by how the grayscale mapping is centered, which is set by the window level. In medical image display, the grayscale values are mapped to brightness using a window level (the center of the range) and a window width (the size of the range). When you adjust the window level, you shift that center up or down, which makes the overall image appear lighter or darker without changing the range of tones shown. Raising the level generally makes the image brighter, while lowering it makes it darker.

Window width, on the other hand, changes the range of gray tones that are displayed. A narrower width increases contrast by narrowing the range of values mapped to the display, while a wider width decreases contrast. Pixel spacing is about the physical distance between pixels and affects spatial resolution, not brightness. Matrix size affects how many pixels compose the image and also influences resolution, not brightness.