The number of pixels per millimeter in an image to the center of the adjacent pixel is called:

• A. Pixel Density
• B. Bit Depth
• C. Pixel Pitch
• D. Matrix Depth

Answer: (A)

The key idea is how many picture elements fit into a given physical length. Pixel density captures this directly: it is the number of pixels per unit length, such as per millimeter. The phrase mentioning distance from the center of one pixel to the center of the next describes how tightly packed the pixels are, and that spacing is called pixel pitch. Pixel density and pixel pitch are reciprocals when you express density in pixels per millimeter (density = 1 / pitch in millimeters). So, if the pitch is 0.25 mm, you’d have 4 pixels per millimeter. Bit depth concerns color information per pixel, not how many pixels fit in a length, and matrix depth isn’t the term used for this measurement. Therefore, the quantity described by “number of pixels per millimeter” is pixel density.