In optical microscopy, it refers to the difference in light intensity between the image’s background and its features, or between different structures within the specimen. This variation in brightness or color allows the observer to distinguish details and discern the morphology of the sample. For instance, unstained biological cells often exhibit minimal differences in refractive index, resulting in low levels; specific staining techniques or specialized illumination methods are then employed to enhance visibility.
Adequate visibility is paramount for accurate observation and interpretation. Without sufficient distinction, fine details may be obscured, rendering qualitative or quantitative analysis unreliable. The development of techniques to improve this has been a driving force in the advancement of microscopic imaging, enabling researchers to visualize increasingly smaller and more subtle structures. Early microscopists relied on staining and manipulation of illumination to improve visibility, and these methods continue to be refined and complemented by advanced optical technologies.
