... The substepping technique is used for the Hubble Space Telescope (HST) imaging to cope with the problem of undersampling and to improve resolution. ... For the HST, undersampling means that the size of the pixel in a camera is larger than the critical value determined by the optics of the telescope, and aliasing takes place. ... Sampling is an operation to integrate a ( x ) within a pixel, and to assign the result to this pixel (Figure 1 A). ... Figure 1: Substepping ( N =2) and normal sampling. ...