Abstract: The Percentage-Closer Soft Shadows（PCSS） technique can generate perceptually accurate soft shadows.PCSS is based on the observation that as the size of the PCF kernel increases，the resulting shadows become softer.The challenge is to vary the filter size intelligently to achieve the correct degree of softness.Using Poisson disk sampling to do the blocker search and the PCF filtering，banding can be reduced without unduly increasing the number of samples.Using a variable depth bias in the direction of the local depth gradient inside the PCF kernel can handle the self-shadowing.So the improved PCSS technique can generate more perceptually accurate soft shadows.