Top: simulated images for different tip-tilt amplitudes applied to the right along the horizontal axis, from left to right: 0.1 λ/D_L, 0.16λ/D_L and 0.38 λ/D_L. Each displayed image is normalized by its maximal value. The dotted circles show the boundaries for the inner and outer areas. Bottom: color-coded representation of the flux asymmetry to emphasize the visual comparison of the asymmetry in the different images. The amplitude of the gradient is equal to the measured differential intensity and all images are shown with the same color scale.