Analysis of maximum speckle contrast in imaging systems

Laser speckle, arising from the high coherence of laser sources, affects the perceived image quality in laser display systems. Speckle contrast serves as a key metric for evaluating speckle visibility. This study presents a physically grounded simulation framework to investigate how imaging system parameters and spatial sampling influence the maximum measurable speckle contrast.The proposed model is based on wave optics and imaging geometry, incorporating real-world parameters such as focal length, aperture size, pixel pitch, and observation distance. The framework is validated through experimental measurements under identical optical conditions. Using this framework, fully developed speckle patterns are simulated, and their degradation under pixel-based sampling by image sensors and retinal sampling by the human eye is examined.Simulation results show that the measured speckle contrast is significantly reduced by spatial averaging effects, especially when speckle size approaches the sampling pitch. For both image sensors and the human retina, the maximum observable contrast falls below the theoretical value due to under-sampling. The visual speckle contrast limit C_VSfull is defined, and a new metric, C_VS, is proposed to evaluate speckle contrast in perceptual contexts. This study bridges physical optics modeling and subjective speckle evaluation, offering insights for speckle assessment and optimization in laser display technologies.