An improved multi-scale Retinex algorithm is proposed and used in face detection

aiming at problem of slow computing speed and amplifies noises in dark area of multi-scale Retinex. To reduce computing iteration calculation

illuminance image is calculated by fast guided filtering

whose parameters is set by the clarity of image. To suppress the noises in dark area

adaptive weighting factor of each scale is calculated according to the brightness information; To eliminate the estimated error

reflection image is smoothed by fast guided filtering. The simulation results show that the proposed algorithm is real-time. The clarity and detection rate is improved by 3. 14 % and 6 %.