The modern epoch ITF series used for the Final Archive (LWP:1992, LWR:1983, and SWP:1985) were obtained in a closely monitored and stable satellite configuration such that any parameters known to affect the image quality (e.g., camera temperature) were carefully controlled. These improved acquisition procedures ensured that the constituent ITF images at each exposure level have little geometric distortion relative to each other. The ITFs for the Final Archive have been constructed in raw space with no attempt to align geometrically the images, because some smoothing of the ITF data is inherent in such an alignment. The raw images for each level were averaged on a pixel-by-pixel basis to form a mean level. If the intensity level of a pixel from one of the component images varied from the mean intensity value for that pixel by more than 2.5 sigma for the SWP and LWR ITFs and 1.4 sigma for the LWP 1992 ITF, the deviant pixel was excluded from the sum. In this way it was possible to use images with missing minor frames in the construction of the ITF. Each level of the ITF is constructed with at least 4 images; the null level was typically constructed with many more images. The resulting ITF for each camera is a three-dimensional file of dimensions 768 × 768 × 12 pixels.
The lowest level of the ITF is a zero exposure or null level which is the background left by the standard camera flood/erase preparation procedure. Correspondingly, the highest level of the ITF has a long enough exposure time to allow the detector to achieve its saturation limit of 255 DN over a majority of the image. The intermediate ITF levels map the camera response through the mid-range of DN values. The 12 level ITF provides sufficient granularity in intensity to allow linear interpolation between the levels.