About Rank 3x3É drop-in for PhotoShop. This file should be placed in the same folder as your other PhotoShop drop-ins, and will then appear in the "Other" submenu under "Filters" This drop-in provides a number of rank operations for monochrome images. It ignores color images. The neigborhood is 3x3 pixels. Ranking of the 9 pixel values is performed using a Shell sort. The dialog allows the user to select several modes: Median filter: a noise removal filter which saves the 5th brightest pixel in each neighborhood. Maximum: saves the brightest pixel in each neighborhood. Often useful for removing dark noise or creating a background to isolate dark features. Minimum: saves the darkest pixel in each neighborhood. Similar in use to the Maximum filter when the noise or features are bright. Range: saves the difference between the brightest and darkest pixels. Useful to create an image showing texture or in some cases edges. Top Hat (+): Ranks the full 3x3 region and saves the difference between the brightest pixel in the region and the original central pixel. Isolates bright points and delineates edges. Top Hat (-): Similar to Top Hat (+) but saves the difference between the darkest pixel in the region and the central pixel. Isolates dark points and delineates edges. Note that for edges, the Top Hat (+) and (-) methods will mark the inside and outside of edges depending on the direction in which brightness varies across it. Hybrid Median: Preserves corners which the conventional median filter rounds off. Separately ranks the 5 pixels forming an X pattern and the 5 pixels forming a + pattern. The median results of these rankings are ranked again along with the original central pixel, and the median of the result saved. After the filter has been run by selection from the "Other" submenu, and the dialog selections made, repeating it by selecting Command-F will use the same dialog selections. To change these, you must again select Rank 3x3 from the submenu. These filters are described in J. C. Russ "The Image Processing Handbook" CRC Press, Boca Raton, FL (1992). The program is Copyright © 1992 by J. C. & J. C. Russ. It may be distributed at no charge provided the copyright notice accompanies the file. John C. & J. Christian Russ 213 Merwin Road Raleigh, NC 27606 fax: 919-851-8117 email: