public void setGamma(float gamma) {
        this.gamma = gamma;
        if (material != null) {
            material.setFloat("Gamma", gamma);
        }
    }
Sets gamma level used to enhance visual quality

@param gamma the desired exponent (default=0.6)
jme3-effects/src/main/java/com/jme3/post/filters/PosterizationFilter.java