Optimization Of Imaging Model And Image Recovery Algorithm In Multi-angle Illuminations Lensless Microscopy Imaging

The invention of microscope opened the door for people to understand the micro world.It has helped human beings to make many significant achievements in life science,medicine,agriculture,material science and many other fields.It has greatly promoted the progress of human civilization.However,due to the limitation of imaging mechanism,traditional optical microscope can’t take into account both high resolution and large field of view imaging.On the other hand,complex optical systems also made microscopes increasingly expensive,cumbersome and difficult to maintain.Lensless microscopy is a new computational imaging technology: without the imaging lens to focus,the sample is directly attached to the imaging sensor to record the diffraction patterns and the object information can be achieved with the corresponding reconstructed method.It is expected to achieve low cost,high portability,large field of view,high resolution and phase imaging.Recently,a mask-modulated lensless imaging with multi-angle illuminations was reported without involving mechanical scanning.In this platform,a programmable LED array is used to generate angle-varied illumination on the object and the detector records the resulting intensity images through an optical mask.The key to successful image recovery is the use of a mask for light field modulation.Such a modulation offers supporting domain constraints.However,the method only achieved a half-pitch resolution of 4.92 μm when using an image sensor with a pixel size of 3.45μm.The achievable resolution is even worse than the sampling resolution allowed by the sensor,which limits its applications in imaging biological samples.Through the analysis of the imaging principle of the scheme,we can see that the main reason for the low resolution and poor quality of the experimental results is the use of weak coherence lighting source in the experiment.In order to solve the problem,we improve the lensless imaging scheme through the following two aspects.First,the imaging model of the lensless imaging scheme is improved.In other words,by exchanging the position of the optical mask and the sample to reduce the distance between object and image sensor,so as to reduce the influence of the LED with weak coherence on the imaging results.Second,based on the improvement of the imaging model,the image restoration algorithm of the imaging scheme is further improved.That is to say,in the reconstruction process,we employ the regularized ptychographic iterative engine and implement an up-sampling process in the reciprocal space.Finally,we still use an image sensor with a pixel size of 3.45 μm in the experiment and 2.46 μm high-resolution is realized.The imaging quality also has been greatly improved.This lensless imaging scheme is expected to be widely used in biomedical and other fields.