Elimination of CCD undersampling effects and subpixeling

Abstract

Charged coupled devices (CCDs) are much common in use in different imaging modalities. In most cases, they mainly limit the resolution of imaging devices. The resolution may be limited by them in two different ways: one by the finite non-zero size of pixels and second by the spacing between the pixels or the pixel pitch. If the pixel spacings do not follow the Nyquist sampling theorem, the information obtained does not represent the true picture of the object. The under-sampling by CCD has been dealt before in literature by placing optical mask at the Fourier plane in a 4f system assuming pixels as point pixels and reusing the same optical mask at the Fourier spectrum of the image captured by the CCD. If the pixels have non-zero width, as they do in reality, the under-sampling cannot be nullified using optical mask alone but a subpixeling in addition to optical mask is also required to remove the aliasing introduced by the nonzero size of the pixels. The three level gray mask at the CCD plane is used that to resolve the CCD pixel into small subpixels while the image and the CCD remain motionless. The intensities were recorded by the CCD at each subpixel step that recovers the information lost due to the averaging nature of the CCD pixels. To our knowledge, we for the first time are combining the optical mask at the Fourier plane in a 4f system and subpixeling of the CCD pixel by using three level gray mask at the CCD plane simultaneously for nullifying the effect of under-sampling by the CCD of finite pixel size.