In domain of reconnaissance, remote sensing etc., people want to get high resolution image. There has a conflict between the resolution and optical system defocus. In order to acquire high resolution image, some ways are taken to minish the defocus, but these ways affect the cost and weight of the system. In this paper, a novel technology was described for extending the depth of focus of incoherent optical systems that does not decrease the resolution of the image. This technology uses generalized aspheric optics to encode images to be invariant to defocus, and digital signal processing to decode the images. It is significant for optical remote sensor to acquire high resolution image under complicated space environment.