``Partial-read'' images are those for which only a portion of the target has been read. By not having a full 768 × 768 array readout, a substantial fraction of the operations overhead time associated with the camera readout and subsequent preparation for the next exposure is reduced. Partial-read images are used only in the low-dispersion mode and are read out such that a camera-dependent rectangular partial image, sufficient to encompass the entire region normally extracted in low-dispersion processing ( Chapter 9), is generated. The partial-read images are preprocessed to imbed the partial-read area into a full 768 × 768 array for which DN values outside of the partial-read area are zero. This is done to enable the normal NEWSIPS processing, which works on 768 × 768 images, to occur without further special consideration of the partial-read nature of the images.
In order to prepare an image file in which to place the partial data, a zero filled blank image of 768 lines by 768 samples is generated. The partial-read data are inserted into the blank image using the positions tabulated by Imhoff (1991).