Nikkei publishes an article with more details on Hitachi lens-less camera:
"In general, the method that Hitachi employed for its lens-less camera uses a "moire stripe" that can be obtained by stacking two concentric-patterned films with a certain interval and transmitting light through them. The numerous light-emitting points constituting the image influence the pitch and orientation of the moire stripe. The location of light, etc can be restored by applying two-dimensional Fourier transformation to the moire stripe.
This time, Hitachi replaced one of the films (one that is closer to the image sensor) with image processing. In other words, one film is placed with an interval of about 1mm, but the other film does not actually exist. And, instead of using the second film, a concentric pattern is superimposed on image data."