Automatic focusing method for lensless digital holographic imaging

The invention provides an automatic focusing method for lensless digital holographic imaging, and the method comprises the steps: carrying out back propagation on a holographic image, and obtaining a holographic reconstruction image; taking guide filtering as a blurred image function, and calculating a direction information difference value between the reconstructed image and the blurred image by adopting a gradient vector square function to obtain an evaluation function of the holographic reconstructed image; and combining a golden section search method with an evaluation function, determining an optimal defocusing amount, and obtaining an optimal reconstructed image. According to the method, a reconstructed holographic image is blurred by adopting a guide filter, and information of the reconstructed image and information of a blurred image in different directions are extracted respectively. The optimal defocusing amount is determined by comparing the change conditions of the direction information of the rec