A lens-free method of microscopic twin-image free imaging a sample containing micro-objects with sub-cellular resolution of the micro-objects comprising: illuminating a sample holder configured to hold the sample with an illumination source emitting at least partially incoherent light to illuminate the sample through a spatial filter, wherein the spatial filter is disposed at a distance z1 from the sample holder and an imaging sensor array having an active area is disposed at a distance z2 from a back side of the sample holder, and wherein z2<<z1 and wherein there are no lenses disposed between the illumination source and the sample and there are no lenses disposed between the sample holder and the imaging sensor array; obtaining one or more image frames from the imaging sensor array, the one or more image frames containing raw hologram amplitude images of the micro-objects; wherein said lens-free method further comprises: processing the one or more image frames containing raw hologram amplitude images of the micro-objects with a processor to recover lost hologram phase information of the micro-objects, said processing comprising upsampling the raw hologram amplitude images followed by iterative interferometric or non-interferometric phase retrieval; and outputting from the processor reconstructed images of the micro-objects based on the raw hologram amplitude images and the lost hologram phase information, wherein the iterative reconstructed images have a sub-pixel resolution compared to the pixel of the imaging sensor array as a consequence of the upsampling and a field-of-view equal to the active area of the imaging sensor array. illuminating a sample holder configured to hold the sample with an illumination source emitting at least partially incoherent light to illuminate the sample through a spatial filter, wherein the spatial filter is disposed at a distance z1 from the sample holder and an imaging sensor array having an active area is disposed at a distance z2 from a back side of the sample holder, and wherein z2<<z1 and wherein there are no lenses disposed between the illumination source and the sample and there are no lenses disposed between the sample holder and the imaging sensor array; obtaining one or more image frames from the imaging sensor array, the one or more image frames containing raw hologram amplitude images of the micro-objects; wherein said lens-free method further comprises: processing the one or more image frames containing raw hologram amplitude images of the micro-objects with a processor to recover lost hologram phase information of the micro-objects, said processing comprising upsampling the raw hologram amplitude images followed by iterative interferometric or non-interferometric phase retrieval; and outputting from the processor reconstructed images of the micro-objects based on the raw hologram amplitude images and the lost hologram phase information, wherein the iterative reconstructed images have a sub-pixel resolution compared to the pixel of the imaging sensor array as a consequence of the upsampling and a field-of-view equal to the active area of the imaging sensor array. processing the one or more image frames containing raw hologram amplitude images of the micro-objects with a processor to recover lost hologram phase information of the micro-objects, said processing comprising upsampling the raw hologram amplitude images followed by iterative interferometric or non-interferometric phase retrieval; and outputting from the processor reconstructed images of the micro-objects based on the raw hologram amplitude images and the lost hologram phase information, wherein the iterative reconstructed images have a sub-pixel resolution compared to the pixel of the imaging sensor array as a consequence of the upsampling and a field-of-view equal to the active area of the imaging sensor array.