Below are examples of the results of the cleaning ("destriping") technique applied to photo LO4-121H2 of the Lunar Orbiter 4 mission. The photo shows the crater Copernicus, its ejecta blanket, chains of secondary craters from Copernicus, and its rays.
BEFORE DESTRIPING AFTER DESTRIPING
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The "before" image was downloaded from the website of the Lunar and Planetary Institute (LPI). Jeff Gillis and Mary Ann Hager and others of the LPI staff digitized this and other pictures from archival hard copy.
I cleaned up the downloaded images using two software programs I wrote for that purpose in Visual Basic. The first program removes the lines caused by light streaks between framelets, an artifact of the ground reconstruction process. Further, it measures and compensates for systematic variations in sensitivity across the framelets caused by the characteristics of the cathode ray tubes used first to scan the images in the spacecraft and then to expose the framelet films on the ground. The second program reduces the remaining systematic artifacts. It performs a two-dimensional Fourier transformation and applies a specially shaped filter to the transformed image, taking advantage of the differences in spectral characteristics between the artifacts and the light pattern from the Moon’surface.
The cleaning process is described in an appendix to my book "Lunar Orbiter Photographic Atlas of the Near Side of the Moon." That appendix can be viewed in full here.
Most of the cleaned high resolution photos from Lunar Orbiter Mission 4 have been printed in the book, and the CD enclosed with the book contains a comprehensive set of both high and medium resolution images from that mission.
I plan to complete the cleaning of the rest of the Lunar Orbiter photos posted on the LPI web site, which were selected and published in "Lunar Orbiter Photographic Atlas of the Moon" by Bowker and Hughes of NASA’s Langley Research Center (LRC managed the Lunar Orbiter project). These remaining images (from Lunar Orbiter 1, 2, 3, and 5) provide coverage of the far side of the Moon, to complement the near side photos from Lunar Orbiter Mission 4.